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<div>APPLYING JAVA<br /> Chapter 32: Scrabblet: A Multiplayer Word Game 1097<br /> mult *= 2;<br /> else if (t == l3)<br /> lscore *= 3;<br /> else if (t == l2)<br /> lscore *= 2;<br /> if (i == -1) {<br /> letters_seen++;<br /> }<br /> }<br /> word_score += lscore;<br /> n++;<br /> x += xinc;<br /> y += yinc;<br /> }<br /> word_score *= mult;<br /> One last error check is done on the main word only. Since the loop ends whenever<br /> it hits a blank square or the edge of the board, it should cover all of the freshly played<br /> tiles, as well as some previously played ones. If it sees fewer tiles, then there must have<br /> been a gap in them, which is an illegal position, so it returns null. If that test is passed,<br /> it checks to see if all seven tiles were played, awarding a 50-point bonus if they were.<br /> After inspecting the main word, findwords( ) inverts the sense of horizontal and looks<br /> for orthogonal words on the subsequent passes.<br /> if (i == -1) {<br /> // first pass...<br /> }<br /> // if we didn't see all the letters, then there was a gap,<br /> // which is an illegal tile position.<br /> if (letters_seen != ntiles) {<br /> return null;<br /> }<br /> if (ntiles == 7) {<br /> turn_score += 50;<br /> }<br /> // after the first pass, switch to looking the other way.<br /> horizontal = !horizontal;</div> <div>260 Java™ 2: The Complete Reference<br /> throw<br /> So far, you have only been catching exceptions that are thrown by the Java run-time<br /> system. However, it is possible for your program to throw an exception explicitly,<br /> using the throw statement. The general form of throw is shown here:<br /> throw ThrowableInstance;<br /> Here, ThrowableInstance must be an object of type Throwable or a subclass of<br /> Throwable. Simple types, such as int or char, as well as non-Throwable classes, such<br /> as String and Object, cannot be used as exceptions. There are two ways you can obtain<br /> a Throwable object: using a parameter into a catch clause, or creating one with the new<br /> operator.<br /> The flow of execution stops immediately after the throw statement; any subsequent<br /> statements are not executed. The nearest enclosing try block is inspected to see if it has<br /> a catch statement that matches the type of the exception. If it does find a match, control<br /> is transferred to that statement. If not, then the next enclosing try statement is<br /> inspected, and so on. If no matching catch is found, then the default exception handler<br /> halts the program and prints the stack trace.<br /> Here is a sample program that creates and throws an exception. The handler that<br /> catches the exception rethrows it to the outer handler.<br /> // Demonstrate throw.<br /> class ThrowDemo {<br /> static void demoproc() {<br /> try {<br /> throw new NullPointerException("demo");<br /> } catch(NullPointerException e) {<br /> System.out.println("Caught inside demoproc.");<br /> throw e; // rethrow the exception<br /> }<br /> }<br /> }<br /> public static void main(String args[]) {<br /> try {<br /> demoproc();<br /> } catch(NullPointerException e) {<br /> System.out.println("Recaught: " + e);<br /> }<br /> }</div> <div>1110 Java™ 2: The Complete Reference<br /> represent the blank tile in slot 0, and A through Z in 1 through 26. The letter_counts<br /> array says how many of each letter are in a full bag. For example, letter_counts[1] is 9,<br /> which says there are nine A tiles in the bag. Similarly, the letter_points array maps<br /> each letter to its point value. The A tiles are worth only 1 point, and the lone Z is worth<br /> 10. There are 100 letters stored in the array called letters. The number of letters actually<br /> left in the bag during game play is stored in n.<br /> import java.util.Random;<br /> class Bag {<br /> private Random rand;<br /> private int letter_counts[] = {<br /> 2, 9, 2, 2, 4, 12, 2, 3, 2, 9, 1, 1, 4, 2,<br /> 6, 8, 2, 1, 6, 4, 6, 4, 2, 2, 1, 2, 1<br /> };<br /> private int letter_points[] = {<br /> 0, 1, 3, 3, 2, 1, 4, 2, 4, 1, 8, 5, 1, 3,<br /> 1, 1, 3, 10, 1, 1, 1, 1, 4, 4, 8, 4, 10<br /> };<br /> private Letter letters[] = new Letter[100];<br /> private int n = 0;<br /> Bag( )<br /> The Bag constructor takes the seed and makes a Random object out of it. It then scans<br /> through the letter_counts array, making the right number of new Letter objects, being<br /> careful to replace the blank tile with an asterisk. It then calls putBack( ) for each letter,<br /> to put them in the bag.<br /> Bag(int seed) {<br /> rand = new Random(seed);<br /> for (int i = 0; i < letter_counts.length; i++) {<br /> for (int j = 0; j < letter_counts[i]; j++) {<br /> Letter l = new Letter(i == 0 ? '*' : (char)('A' + i - 1),<br /> letter_points[i]);<br /> putBack(l);<br /> }<br /> }<br /> }</div> <div>890 Java™ 2: The Complete Reference<br /> Second, the OurButton Bean provides a push-button functionality. We will have one<br /> button labeled “Rotate X” to rotate the molecule along its X axis and another button<br /> labeled “Rotate Y” to rotate the molecule along its Y axis.<br /> Figure 25-2 shows how this application appears.<br /> Create and Configure an Instance of the Molecule Bean<br /> Follow these steps to create and configure an instance of the Molecule Bean:<br /> 1. Position the cursor on the ToolBox entry labeled Molecule and click the left<br /> mouse button. You should see the cursor change to a cross.<br /> 2. Move the cursor to the BeanBox display area and click the left mouse button in<br /> approximately the area where you wish the Bean to be displayed. You should<br /> see a rectangular region appear that contains a 3-D display of a molecule. This<br /> area is surrounded by a hatched border, indicating that it is currently selected.<br /> 3. You can reposition the Molecule Bean by positioning the cursor over one of the<br /> hatched borders and dragging the Bean.<br /> 4. You can change the molecule that is displayed by changing the selection in the<br /> Properties window. Notice that the Bean display changes immediately when<br /> you change the selected molecule.<br /> Figure 25-2.<br /> The Molecule and OurButton Beans</div> <div>666 Java™ 2: The Complete Reference<br /> If a mouse has a wheel, it is located between the left and right buttons. Mouse wheels<br /> are used for scrolling. MouseWheelEvent defines these two integer constants.<br /> WHEEL_BLOCK_SCROLL<br /> WHEEL_UNIT_SCROLL<br /> A page-up or page-down scroll event occurred.<br /> A line-up or line-down scroll event occurred.<br /> MouseWheelEvent defines the following constructor.<br /> MouseWheelEvent(Component src, int type, long when, int modifiers,<br /> int x, int y, int clicks, boolean triggersPopup,<br /> int scrollHow, int amount, int count)<br /> Here, src is a reference to the object that generated the event. The type of the event<br /> is specified by type. The system time at which the mouse event occurred is passed in<br /> when. The modifiers argument indicates which modifiers were pressed when the event<br /> occurred. The coordinates of the mouse are passed in x and y. The number of clicks<br /> the wheel has rotated is passed in clicks. The triggersPopup flag indicates if this event<br /> causes a pop-up menu to appear on this platform. The scrollHow value must be either<br /> WHEEL_UNIT_SCROLL or WHEEL_BLOCK_SCROLL. The number of units to scroll<br /> is passed in amount. The count parameter indicates the number of rotational units that<br /> the wheel moved.<br /> MouseWheelEvent defines methods that give you access to the wheel event.<br /> To obtain the number of rotational units, call getWheelRotation( ), shown here.<br /> int getWheelRotation( )<br /> It returns the number of rotational units. If the value is positive, the wheel moved<br /> counterclockwise. If the value is negative, the wheel moved clockwise.<br /> To obtain the type of scroll, call getScrollType( ), shown next.<br /> int getScrollType( )<br /> It returns either WHEEL_UNIT_SCROLL or WHEEL_BLOCK_SCROLL.<br /> If the scroll type is WHEEL_UNIT_SCROLL, you can obtain the number of units<br /> to scroll by calling getScrollAmount( ). It is shown here.<br /> int getScrollAmount( )<br /> The TextEvent Class<br /> Instances of this class describe text events. These are generated by text fields and text<br /> areas when characters are entered by a user or program. TextEvent defines the integer<br /> constant TEXT_VALUE_CHANGED.<br /> The one constructor for this class is shown here:<br /> TextEvent(Object src, int type)</div> <div>394 Java™ 2: The Complete Reference<br /> Method<br /> static Long decode(String str)<br /> throws NumberFormatException<br /> double doubleValue( )<br /> boolean equals(Object LongObj)<br /> float floatValue( )<br /> static Long getLong(String propertyName)<br /> static Long getLong(String propertyName,<br /> long default)<br /> static Long getLong(String propertyName,<br /> Long default)<br /> int hashCode( )<br /> int intValue( )<br /> long longValue( )<br /> Description<br /> Returns a Long object that<br /> contains the value specified by<br /> the string in str.<br /> Returns the value of the invoking<br /> object as a double.<br /> Returns true if the invoking long<br /> object is equivalent to LongObj.<br /> Otherwise, it returns false.<br /> Returns the value of the invoking<br /> object as a float.<br /> Returns the value associated<br /> with the environmental property<br /> specified by propertyName. A<br /> null is returned on failure.<br /> Returns the value associated<br /> with the environmental property<br /> specified by propertyName.<br /> The value of default is returned<br /> on failure.<br /> Returns the value associated<br /> with the environmental property<br /> specified by propertyName.<br /> The value of default is returned<br /> on failure.<br /> Returns the hash code for the<br /> invoking object.<br /> Returns the value of the invoking<br /> object as an int.<br /> Returns the value of the invoking<br /> object as a long.<br /> Table 14-6.<br /> The Methods Defined by Long (continued)</div> <div>THE JAVA LIBRARY<br /> Chapter 18: Networking 595<br /> Applets may only establish socket connections back to the host from which the applet was<br /> downloaded. This restriction exists because it would be dangerous for applets loaded<br /> through a firewall to have access to any arbitrary machine.<br /> There are two kinds of TCP sockets in Java. One is for servers, and the other is for<br /> clients. The ServerSocket class is designed to be a “listener,” which waits for clients to<br /> connect before doing anything. The Socket class is designed to connect to server<br /> sockets and initiate protocol exchanges.<br /> The creation of a Socket object implicitly establishes a connection between the client<br /> and server. There are no methods or constructors that explicitly expose the details of<br /> establishing that connection. Here are two constructors used to create client sockets:<br /> Socket(String hostName, int port)<br /> Socket(InetAddress ipAddress, int port)<br /> Creates a socket connecting the local<br /> host to the named host and port; can<br /> throw an UnknownHostException or<br /> an IOException.<br /> Creates a socket using a preexisting<br /> InetAddress object and a port; can throw<br /> an IOException.<br /> A socket can be examined at any time for the address and port information<br /> associated with it, by use of the following methods:<br /> InetAddress getInetAddress( )<br /> int getPort( )<br /> int getLocalPort( )<br /> Returns the InetAddress associated with<br /> the Socket object.<br /> Returns the remote port to which this<br /> Socket object is connected.<br /> Returns the local port to which this<br /> Socket object is connected.<br /> Once the Socket object has been created, it can also be examined to gain access to<br /> the input and output streams associated with it. Each of these methods can throw an<br /> IOException if the sockets have been invalidated by a loss of connection on the Net.<br /> These streams are used exactly like the I/O streams described in Chapter 17 to send<br /> and receive data.<br /> InputStream getInputStream( )<br /> OutputStream getOutputStream( )<br /> Returns the InputStream associated<br /> with the invoking socket.<br /> Returns the OutputStream associated<br /> with the invoking socket.</div> <div>1138 Java™ 2: The Complete Reference<br /> Here, release is a string that designates the release or version in which this feature<br /> became available. The @since tag can be used in documentation for variables, methods,<br /> and classes.<br /> @throws<br /> The @throws tag has the same meaning as the @exception tag.<br /> {@value}<br /> Displays the value of a constant, which must be a static field.<br /> @version<br /> The @version tag specifies the version of a class. It has the following syntax:<br /> @version info<br /> Here, info is a string that contains version information, typically a version number,<br /> such as 2.2. The @version tag can be used only in documentation for a class. You may<br /> need to specify the -version option when executing javadoc in order for the @version<br /> field to be included in the HTML documentation.<br /> The General Form of a Documentation<br /> Comment<br /> After the beginning /**, the first line or lines become the main description of your class,<br /> variable, or method. After that, you can include one or more of the various @ tags. Each<br /> @ tag must start at the beginning of a new line or follow an asterisk (*) that is at the<br /> start of a line. Multiple tags of the same type should be grouped together. For example,<br /> if you have three @see tags, put them one after the other.<br /> Here is an example of a documentation comment for a class:<br /> /**<br /> * This class draws a bar chart.<br /> * @author Herbert Schildt<br /> * @version 3.2<br /> */<br /> What javadoc Outputs<br /> The javadoc program takes as input your Java program’s source file and outputs<br /> several HTML files that contain the program’s documentation. Information about each</div> <div>THE JAVA LIBRARY<br /> Chapter 17: Input/Output: Exploring java.io 539<br /> The ObjectInputStream.GetField and ObjectOutputStream.PutField inner classes<br /> were added by Java 2. The java.io package also contains two classes that were deprecated<br /> by Java 2 and are not shown in the preceding table: LineNumberInputStream and<br /> StringBufferInputStream. These classes should not be used for new code.<br /> The following interfaces are defined by java.io:<br /> DataInput FilenameFilter ObjectOutput<br /> DataOutput ObjectInput ObjectStreamConstants<br /> Externalizable ObjectInputValidation Serializable<br /> FileFilter<br /> The FileFilter interface was added by Java 2.<br /> As you can see, there are many classes and interfaces in the java.io package. These<br /> include byte and character streams, and object serialization (the storage and retrieval of<br /> objects). This chapter examines several of the most commonly used I/O components,<br /> beginning with one of the most unique: File.<br /> File<br /> Although most of the classes defined by java.io operate on streams, the File class does<br /> not. It deals directly with files and the file system. That is, the File class does not<br /> specify how information is retrieved from or stored in files; it describes the properties<br /> of a file itself. A File object is used to obtain or manipulate the information associated<br /> with a disk file, such as the permissions, time, date, and directory path, and to navigate<br /> subdirectory hierarchies.<br /> Files are a primary source and destination for data within many programs.<br /> Although there are severe restrictions on their use within applets for security reasons,<br /> files are still a central resource for storing persistent and shared information. A<br /> directory in Java is treated simply as a File with one additional property—a list of<br /> filenames that can be examined by the list( ) method.<br /> The following constructors can be used to create File objects:<br /> File(String directoryPath)<br /> File(String directoryPath, String filename)<br /> File(File dirObj, String filename)<br /> File(URI uriObj)<br /> Here, directoryPath is the path name of the file, filename is the name of the file, dirObj is a<br /> File object that specifies a directory, and uriObj is a URI object that describes a file. The<br /> fourth constructor was added by Java 2, version 1.4.<br /> The following example creates three files: f1, f2, and f3. The first File object is<br /> constructed with a directory path as the only argument. The second includes two<br /> arguments—the path and the filename. The third includes the file path assigned to f1<br /> and a filename; f3 refers to the same file as f2.</div> <div>594 Java™ 2: The Complete Reference<br /> Here is the output produced by this program. (Of course, the output you see will be<br /> slightly different.)<br /> default/206.148.209.138<br /> osborne.com/198.45.24.162<br /> www.nba.com/64.241.238.153<br /> www.nba.com/64.241.238.142<br /> Instance Methods<br /> The InetAddress class also has several other methods, which can be used on the objects<br /> returned by the methods just discussed. Here are some of the most commonly used.<br /> boolean equals(Object other)<br /> byte[ ] getAddress( )<br /> String getHostAddress( )<br /> String getHostName( )<br /> boolean isMulticastAddress( )<br /> String toString( )<br /> Returns true if this object has the same Internet<br /> address as other.<br /> Returns a byte array that represents the object’s<br /> Internet address in network byte order.<br /> Returns a string that represents the host address<br /> associated with the InetAddress object.<br /> Returns a string that represents the host name<br /> associated with the InetAddress object.<br /> Returns true if this Internet address is a multicast<br /> address. Otherwise, it returns false.<br /> Returns a string that lists the host name and the<br /> IP address for convenience.<br /> Internet addresses are looked up in a series of hierarchically cached servers. That<br /> means that your local computer might know a particular name-to-IP-address mapping<br /> automatically, such as for itself and nearby servers. For other names, it may ask a local<br /> DNS server for IP address information. If that server doesn’t have a particular address,<br /> it can go to a remote site and ask for it. This can continue all the way up to the root<br /> server, called InterNIC (internic.net). This process might take a long time, so it is wise<br /> to structure your code so that you cache IP address information locally rather than look<br /> it up repeatedly.<br /> TCP/IP Client Sockets<br /> TCP/IP sockets are used to implement reliable, bidirectional, persistent, point-to- point,<br /> stream-based connections between hosts on the Internet. A socket can be used to connect<br /> Java’s I/O system to other programs that may reside either on the local machine or on<br /> any other machine on the Internet.</div> <div>THE JAVA LANGUAGE<br /> Chapter 12: I/O, Applets, and Other Topics 329<br /> import java.awt.*;<br /> import java.applet.*;<br /> public class SimpleApplet extends Applet {<br /> public void paint(Graphics g) {<br /> g.drawString("A Simple Applet", 20, 20);<br /> }<br /> }<br /> This applet begins with two import statements. The first imports the Abstract Window<br /> Toolkit (AWT) classes. Applets interact with the user through the AWT, not through the<br /> console-based I/O classes. The AWT contains support for a window-based, graphical<br /> interface. As you might expect, the AWT is quite large and sophisticated, and a complete<br /> discussion of it consumes several chapters in Part II of this book. Fortunately, this simple<br /> applet makes very limited use of the AWT. The second import statement imports the<br /> applet package, which contains the class Applet. Every applet that you create must be a<br /> subclass of Applet.<br /> The next line in the program declares the class SimpleApplet. This class must be<br /> declared as public, because it will be accessed by code that is outside the program.<br /> Inside SimpleApplet, paint( ) is declared. This method is defined by the AWT<br /> and must be overridden by the applet. paint( ) is called each time that the applet<br /> must redisplay its output. This situation can occur for several reasons. For example,<br /> the window in which the applet is running can be overwritten by another window and<br /> then uncovered. Or, the applet window can be minimized and then restored. paint( ) is<br /> also called when the applet begins execution. Whatever the cause, whenever the applet<br /> must redraw its output, paint( ) is called. The paint( ) method has one parameter of<br /> type Graphics. This parameter contains the graphics context, which describes the<br /> graphics environment in which the applet is running. This context is used whenever<br /> output to the applet is required.<br /> Inside paint( ) is a call to drawString( ), which is a member of the Graphics class.<br /> This method outputs a string beginning at the specified X,Y location. It has the<br /> following general form:<br /> void drawString(String message, int x, int y)<br /> Here, message is the string to be output beginning at x,y. In a Java window, the upper-left<br /> corner is location 0,0. The call to drawString( ) in the applet causes the message “A Simple<br /> Applet” to be displayed beginning at location 20,20.<br /> Notice that the applet does not have a main( ) method. Unlike Java programs, applets<br /> do not begin execution at main( ).Infact, most applets don’t even have a main( ) method.<br /> Instead, an applet begins execution when the name of its class is passed to an applet viewer<br /> or to a network browser.</div> <div>THE JAVA LIBRARY<br /> Chapter 16: java.util Part 2: More Utility Classes 509<br /> Method<br /> void flip(int index)<br /> void flip(int startIndex,<br /> int endIndex)<br /> boolean get(int index)<br /> BitSet get(int startIndex,<br /> int endIndex)<br /> int hashCode( )<br /> boolean intersects(BitSet bitSet)<br /> boolean isEmpty( )<br /> int length( )<br /> int nextClearBit(int startIndex)<br /> int nextSetBit(int startIndex)<br /> void or(BitSet bitSet)<br /> void set(int index)<br /> Description<br /> Reverses the bit specified by index. (Added by<br /> Java 2, version 1.4)<br /> Reverses the bits from startIndex to endIndex–1.<br /> (Added by Java 2, version 1.4)<br /> Returns the current state of the bit at the<br /> specified index.<br /> Returns a BitSet that consists of the bits from<br /> startIndex to endIndex–1. The invoking object is<br /> not changed. (Added by Java 2, version 1.4)<br /> Returns the hash code for the invoking object.<br /> Returns true if at least one pair of corresponding<br /> bits within the invoking object and bitSet are 1.<br /> (Added by Java 2, version 1.4)<br /> Returns true if all bits in the invoking object<br /> are zero. (Added by Java 2, version 1.4)<br /> Returns the number of bits required to hold<br /> the contents of the invoking BitSet. This value<br /> is determined by the location of the last 1 bit.<br /> (Added by Java 2)<br /> Returns the index of the next cleared bit, (that<br /> is, the next zero bit), starting from the index<br /> specified by startIndex. (Added by Java 2,<br /> version 1.4)<br /> Returns the index of the next set bit (that is, the<br /> next 1 bit), starting from the index specified by<br /> startIndex.Ifnobit is set, –1 is returned. (Added<br /> by Java 2, version 1.4)<br /> ORs the contents of the invoking BitSet object<br /> with that specified by bitSet. The result is<br /> placed into the invoking object.<br /> Sets the bit specified by index.<br /> Table 16-2.<br /> The Methods Defined by BitSet (continued)</div> <div>Index 1153<br /> concatenating, 185–186,<br /> 352–353. 364, 372–373<br /> creating, 348–351<br /> extracting characters from,<br /> 355–356<br /> length, obtaining,<br /> 186–187, 351<br /> literals, 52, 351<br /> modifying, 363–366<br /> as objects, 52, 70–71,<br /> 181–182, 348<br /> parsing formatted input, 506<br /> reading, 320–322<br /> representations of numbers,<br /> converting, 392–393, 396<br /> searching, 361–363<br /> String class, 28, 185, 348<br /> constructors, 348–350<br /> StringBuffer class, 185, 348, 361,<br /> 369–377<br /> StringBufferInputStream class, 539<br /> StringIndexOutOfBounds<br /> exception, 266<br /> StringTokenizer class, 506–508<br /> methods, table of, 507<br /> stringWidth( ), 725, 726<br /> Stroustrup, Bjarne, 7<br /> Stubs (RMI), 876–877<br /> Subclass, 190, 192<br /> subList( ), 446, 447<br /> subMap( ), 465<br /> subSequence( ), 368, 376<br /> subSet( ), 447, 448<br /> substring( ), 363–364, 375<br /> Sun Microsystems, 7, 588<br /> super, 176, 197–203<br /> and superclass constructors,<br /> 197–202, 206<br /> and instance variables,<br /> 202–203<br /> Superclass, 190, 192<br /> suspend( ), 15, 305–307, 308,<br /> 424, 426<br /> Swing, 922–948<br /> and Bean Builder, 891<br /> component classes, list of<br /> some, 922<br /> switch statement, 104–108<br /> Synchronization, 276, 292–297<br /> and collections, 475<br /> and deadlock, 302–304<br /> race condition and, 294<br /> via synchronized block,<br /> 295–297<br /> via synchronized method,<br /> 292–295<br /> synchronized modifier, 292<br /> used with method, 292,<br /> 295<br /> used with object, 295–297<br /> synchronizedList( ), 475, 478<br /> synchronizedSet( ), 475, 478<br /> System class, 29, 318, 407<br /> methods, table of, 408–410<br /> System.err standard error<br /> stream, 318<br /> System.in standard input stream,<br /> 318, 319<br /> System.in.read( ), 114<br /> System.out standard output<br /> stream, 318, 322, 323, 324<br /> T<br /> Tabbed panes, 936–939<br /> Tables, Swing, 946–948<br /> tailMap( ), 465<br /> tailSet( ), 447, 448<br /> tan( ), 420<br /> TCP/IP, 15, 588, 1070<br /> client sockets, 594–597<br /> disadvantages of, 623<br /> reserved sockets, 589–590<br /> server sockets, 601–602<br /> See also Transmission<br /> Control Protocol (TCP)<br /> Temple, Robert, 1012<br /> Ternary operator (?:), 92, 95–96<br /> Text fields, 758–761<br /> Swing, 925–926<br /> Text formatting, 878–882<br /> Text output, managing, 723–733<br /> TextArea class, 761–763<br /> textChanged( ), 672<br /> TextComponent class, 758, 761<br /> TextEvent class, 658, 666–667<br /> TextField class, 758, 759<br /> TextListener interface, 669, 672<br /> this, 149–150, 176<br /> Thompson, Ken, 5, 588<br /> Thread(s)<br /> creating, 280–286<br /> daemon, 532<br /> and deadlock, 302–304, 308<br /> definition of, 274<br /> group, 279, 426–432<br /> main, 277, 282, 286<br /> messaging, 276–277, 297–302<br /> possible states of, 275<br /> priorities, 275–276,<br /> 289–292, 423<br /> resuming, 305–310, 426<br /> stopping, 305–310<br /> suspending, 277, 278, 279,<br /> 305–310, 426<br /> synchronization. See<br /> Synchronization<br /> Thread class, 15, 277,<br /> 423–426, 531<br /> constructors, 280, 284, 423<br /> extending, 282–284<br /> methods, table of, 424–426<br /> ThreadGroup class, 426–432<br /> methods, table of, 427–428<br /> ThreadLocal class, 380, 432<br /> throw, 250, 260–261<br /> Throwable class, 251, 254, 267,<br /> 269–270, 434<br /> methods defined by, table<br /> of, 267<br /> obtaining object of, 260–261<br /> throws, 250, 261–262, 265<br /> TickTock Bean, 902–903<br /> Time. See Date class<br /> Timer class, 531–534<br /> TimerTask class, 531–534<br /> Timestamps, 659<br /> TimeZone class, 521–522<br /> methods defined by, table<br /> of, 521–522<br /> toArray( ), 444, 445, 451–452<br /> toBinaryString( ), 397<br /> toCharArray( ), 356<br /> toDegrees( ), 422<br /> toHexString( ), 397<br /> Tokens, 506<br /> toLowerCase( ), 367<br /> Tomcat, 951–952<br /> toOctalString( ), 397<br /> Toolkit class, 720<br /> toRadians( ), 422<br /> toString( ), 221, 254, 268, 323,<br /> 353–354, 366, 387, 456, 510,<br /> 511, 656<br /> totalMemory( ), 404, 405–406<br /> toUpperCase( ), 367<br /> transient modifier, 331–332<br /> translatePoint( ), 665<br /> Transmission Control<br /> Protocol (TCP)<br /> definition of, 589<br /> and stream-based I/O, 592<br /> See also TCP/IP<br /> TreeExpansionEvent class, 942<br /> TreeExpansionListener<br /> interface, 942<br /> TreeMap class, 466, 468–470, 504<br /> TreeNode class, 942</div> <div>816 Java™ 2: The Complete Reference<br /> Figure 23-4.<br /> Sample output from TrackedImageLoad<br /> 0 and fully opaque is 255. The width and height of the resulting image are passed in<br /> width and height. The starting point in the pixel array to begin reading data is passed in<br /> offset. The width of a scan line (which is often the same as the width of the image) is<br /> passed in scanLineWidth.<br /> The following short example generates a MemoryImageSource object using a<br /> variation on a simple algorithm (a bitwise-exclusive-OR of the x and y address of each<br /> pixel) from the book Beyond Photography, The Digital Darkroom by Gerard J. Holzmann<br /> (Prentice Hall, 1988).</div> <div>50 Java™ 2: The Complete Reference<br /> A Closer Look at Literals<br /> Literals were mentioned briefly in Chapter 2. Now that the built-in types have been<br /> formally described, let’s take a closer look at them.<br /> Integer Literals<br /> Integers are probably the most commonly used type in the typical program. Any whole<br /> number value is an integer literal. Examples are 1, 2, 3, and 42. These are all decimal<br /> values, meaning they are describing a base 10 number. There are two other bases which<br /> can be used in integer literals, octal (base eight) and hexadecimal (base 16). Octal values<br /> are denoted in Java by a leading zero. Normal decimal numbers cannot have a leading<br /> zero. Thus, the seemingly valid value 09 will produce an error from the compiler,<br /> since 9 is outside of octal’s 0 to 7 range. A more common base for numbers used by<br /> programmers is hexadecimal, which matches cleanly with modulo 8 word sizes, such<br /> as 8, 16, 32, and 64 bits. You signify a hexadecimal constant with a leading zero-x, (0x<br /> or 0X). The range of a hexadecimal digit is 0 to 15, so A through F (or a through f ) are<br /> substituted for 10 through 15.<br /> Integer literals create an int value, which in Java is a 32-bit integer value. Since<br /> Java is strongly typed, you might be wondering how it is possible to assign an integer<br /> literal to one of Java’s other integer types, such as byte or long, without causing a type<br /> mismatch error. Fortunately, such situations are easily handled. When a literal value is<br /> assigned to a byte or short variable, no error is generated if the literal value is within the<br /> range of the target type. Also, an integer literal can always be assigned to a long variable.<br /> However, to specify a long literal, you will need to explicitly tell the compiler that the<br /> literal value is of type long. You do this by appending an upper- or lowercase L to<br /> the literal. For example, 0x7ffffffffffffffL or 9223372036854775807L is the largest long.<br /> Floating-Point Literals<br /> Floating-point numbers represent decimal values with a fractional component. They<br /> can be expressed in either standard or scientific notation. Standard notation consists<br /> of a whole number component followed by a decimal point followed by a fractional<br /> component. For example, 2.0, 3.14159, and 0.6667 represent valid standard-notation<br /> floating-point numbers. Scientific notation uses a standard-notation, floating-point number<br /> plus a suffix that specifies a power of 10 by which the number is to be multiplied. The<br /> exponent is indicated by an E or e followed by a decimal number, which can be positive<br /> or negative. Examples include 6.022E23, 314159E–05, and 2e+100.<br /> Floating-point literals in Java default to double precision. To specify a float literal,<br /> you must append an F or f to the constant. You can also explicitly specify a double literal<br /> by appending a D or d. Doing so is, of course, redundant. The default double type<br /> consumes 64 bits of storage, while the less-accurate float type requires only 32 bits.</div> <div>436 Java™ 2: The Complete Reference<br /> Method<br /> char charAt(int idx)<br /> int length( )<br /> CharSequence<br /> subSequence(int startIdx, int stopIdx)<br /> String toString( )<br /> Description<br /> Returns the character at the index<br /> specified by idx.<br /> Returns the number of characters in<br /> the invoking sequence.<br /> Returns a subset of the invoking<br /> sequence beginning at startIdx and<br /> ending at stopIdx–1.<br /> Returns the String equivalent of the<br /> invoking sequence.<br /> Table 14-20.<br /> The Methods Defined by CharSequence<br /> The CharSequence Interface<br /> Java 2, version 1.4 adds the CharSequence interface. CharSequence defines methods<br /> that grant read-only access to a sequence of characters. These methods are shown<br /> in Table 14-20. This interface is implemented by String and StringBuffer. It is also<br /> implemented by CharBuffer, which is in the new java.nio package (described later<br /> in this book).<br /> The Comparable Interface<br /> Objects of classes that implement Comparable can be ordered. In other words, classes<br /> that implement Comparable contain objects that can be compared in some meaningful<br /> manner. The Comparable interface declares one method that is used to determine what<br /> Java 2 calls the natural ordering of instances of a class. The signature of the method is<br /> shown here:<br /> int compareTo(Object obj)<br /> This method compares the invoking object with obj. It returns 0 if the values are equal.<br /> A negative value is returned if the invoking object has a lower value. Otherwise, a<br /> positive value is returned.<br /> This interface is implemented by several of the classes already reviewed in this<br /> book. Specifically, the Byte, Character, Double, Float, Long, Short, String, and Integer<br /> classes define a compareTo( ) method. In addition, as the next chapter explains, objects<br /> that implement this interface can be used in various collections. Comparable was<br /> added by Java 2.</div> <div>THE JAVA LANGUAGE<br /> Chapter 8: Inheritance 193<br /> }<br /> void sum() {<br /> total = i + j; // ERROR, j is not accessible here<br /> }<br /> class Access {<br /> public static void main(String args[]) {<br /> B subOb = new B();<br /> subOb.setij(10, 12);<br /> }<br /> }<br /> subOb.sum();<br /> System.out.println("Total is " + subOb.total);<br /> This program will not compile because the reference to j inside the sum( ) method<br /> of B causes an access violation. Since j is declared as private, it is only accessible by<br /> other members of its own class. Subclasses have no access to it.<br /> A class member that has been declared as private will remain private to its class. It is not<br /> accessible by any code outside its class, including subclasses.<br /> A More Practical Example<br /> Let’s look at a more practical example that will help illustrate the power of inheritance.<br /> Here, the final version of the Box class developed in the preceding chapter will be<br /> extended to include a fourth component called weight. Thus, the new class will contain<br /> a box’s width, height, depth, and weight.<br /> // This program uses inheritance to extend Box.<br /> class Box {<br /> double width;<br /> double height;<br /> double depth;<br /> // construct clone of an object<br /> Box(Box ob) { // pass object to constructor<br /> width = ob.width;<br /> height = ob.height;</div> <div>THE JAVA LIBRARY<br /> Chapter 14: Exploring java.lang 389<br /> Method<br /> static String toString(byte num)<br /> static Byte valueOf(String str)<br /> throws NumberFormatException<br /> static Byte valueOf(String str, int radix)<br /> throws NumberFormatException<br /> Description<br /> Returns a string that contains the<br /> decimal equivalent of num.<br /> Returns a Byte object that contains<br /> the value specified by the string<br /> in str.<br /> Returns a Byte object that contains<br /> the value specified by the string in<br /> str using the specified radix.<br /> Table 14-3.<br /> The Methods Defined by Byte (continued)<br /> Method<br /> byte byteValue( )<br /> int compareTo(Short s)<br /> int compareTo(Object obj)<br /> static Short decode(String str)<br /> throws NumberFormatException<br /> Description<br /> Returns the value of the invoking<br /> object as a byte.<br /> Compares the numerical value of<br /> the invoking object with that of s.<br /> Returns 0 if the values are equal.<br /> Returns a negative value if the<br /> invoking object has a lower value.<br /> Returns a positive value if the<br /> invoking object has a greater value.<br /> (Added by Java 2)<br /> Operates identically to<br /> compareTo(Short) if obj is of<br /> class Short. Otherwise, throws<br /> a ClassCastException. (Added<br /> by Java 2)<br /> Returns a Short object that<br /> contains the value specified by<br /> the string in str.<br /> Table 14-4.<br /> The Methods Defined by Short</div> <div>146 Java™ 2: The Complete Reference<br /> }<br /> double depth;<br /> // This is the constructor for Box.<br /> Box() {<br /> System.out.println("Constructing Box");<br /> width = 10;<br /> height = 10;<br /> depth = 10;<br /> }<br /> // compute and return volume<br /> double volume() {<br /> return width * height * depth;<br /> }<br /> class BoxDemo6 {<br /> public static void main(String args[]) {<br /> // declare, allocate, and initialize Box objects<br /> Box mybox1 = new Box();<br /> Box mybox2 = new Box();<br /> double vol;<br /> // get volume of first box<br /> vol = mybox1.volume();<br /> System.out.println("Volume is " + vol);<br /> }<br /> }<br /> // get volume of second box<br /> vol = mybox2.volume();<br /> System.out.println("Volume is " + vol);<br /> When this program is run, it generates the following results:<br /> Constructing Box<br /> Constructing Box<br /> Volume is 1000.0<br /> Volume is 1000.0</div> <div>326 Java™ 2: The Complete Reference<br /> class ShowFile {<br /> public static void main(String args[])<br /> throws IOException<br /> {<br /> int i;<br /> FileInputStream fin;<br /> try {<br /> fin = new FileInputStream(args[0]);<br /> } catch(FileNotFoundException e) {<br /> System.out.println("File Not Found");<br /> return;<br /> } catch(ArrayIndexOutOfBoundsException e) {<br /> System.out.println("Usage: ShowFile File");<br /> return;<br /> }<br /> // read characters until EOF is encountered<br /> do {<br /> i = fin.read();<br /> if(i != -1) System.out.print((char) i);<br /> } while(i != -1);<br /> }<br /> }<br /> fin.close();<br /> To write to a file, you will use the write( ) method defined by FileOutputStream.<br /> Its simplest form is shown here:<br /> void write(int byteval) throws IOException<br /> This method writes the byte specified by byteval to the file. Although byteval is declared<br /> as an integer, only the low-order eight bits are written to the file. If an error occurs<br /> during writing, an IOException is thrown. The next example uses write( ) to copy a<br /> text file:<br /> /* Copy a text file.<br /> To use this program, specify the name<br /> of the source file and the destination file.</div> <div>1128 Java™ 2: The Complete Reference<br /> }<br /> out = s.getOutputStream();<br /> host = s.getInetAddress().getHostName();<br /> id = "" + i;<br /> // tell the new one who it is...<br /> write("id " + id + CRLF);<br /> new Thread(this).start();<br /> } catch (IOException e) {<br /> System.out.println("failed ClientConnection " + e);<br /> }<br /> toString( )<br /> We override toString( ) so that we can have a clean representation of this connection<br /> for logging.<br /> public String toString() {<br /> return id + " " + host + " " + name;<br /> }<br /> getHost( ), getId( ), isBusy( ), and setBusy( )<br /> We wrap host, id, and busy in public methods to allow read-only access.<br /> public String getHost() {<br /> return host;<br /> }<br /> public String getId() {<br /> return id;<br /> }<br /> public boolean isBusy() {<br /> return busy;<br /> }<br /> public void setBusy(boolean b) {<br /> busy = b;<br /> }</div> <div>Chapter 16<br /> java.util Part 2: More<br /> Utility Classes<br /> 505</div> <div>APPLYING JAVA<br /> Chapter 29: The DynamicBillboard Applet 1035<br /> }<br /> }<br /> fill_pixels = new int[width];<br /> for(int f = 0; f < width; ++f) {<br /> fill_pixels[f] = 0xFFFFFFFF;<br /> }<br /> int drop_amount;<br /> int location;<br /> public void init(Component owner, int[] current, int[] next) {<br /> init(owner, current, next, CELLS, 160);<br /> setupFillPixels(cell_w);<br /> drop_amount = (cell_h / CELLS) * cell_w;<br /> location = pixels_per_cell - ((cell_h / CELLS) / 2) * cell_w;<br /> for(int c = CELLS - 1; c >= 0; --c) {<br /> try { Thread.sleep(100); } catch (InterruptedException e) {}<br /> Smash(c + 1);<br /> try { Thread.sleep(150); } catch (InterruptedException e) {}<br /> createCellFromWorkPixels(c);<br /> location -= drop_amount;<br /> }<br /> work_pixels = null;<br /> }<br /> void Smash(int max_fold) {<br /> System.arraycopy(next_pixels, pixels_per_cell - location,<br /> work_pixels, 0, location);<br /> int height = cell_h - location / cell_w;<br /> float fold_offset_adder = (float)max_fold * FOLDS / (float)height;<br /> float fold_offset = 0.0f;<br /> int fold_width = cell_w - max_fold;<br /> float src_y_adder = (float)cell_h / (float)height;<br /> float src_y_offset = cell_h - src_y_adder / 2;<br /> for(int p = pixels_per_cell - cell_w; p >= location; p -=<br /> cell_w) {<br /> System.arraycopy(fill_pixels, 0, work_pixels, p, cell_w);<br /> System.arraycopy(current_pixels, (int)src_y_offset * cell_w,<br /> work_pixels, p + (int)fold_offset, fold_width);<br /> src_y_offset -= src_y_adder;<br /> fold_offset += fold_offset_adder;</div> <div>APPLYING JAVA<br /> Chapter 31: The Lavatron Applet: A Sports Arena Display 1059<br /> How Lavatron Works<br /> Lavatron is able to present an interesting image onscreen because of a small trick that it<br /> employs, and its side effect allows the applet to load very quickly. The reason it loads<br /> so quickly is that there isn’t much data transmitted over the Net. The source image is a<br /> JPEG image that is 64 times smaller than the displayed image. Each pixel in the source<br /> image is scaled up to an 8×8-pixel square. Here is the trick that Lavatron uses to<br /> produce the lightbulb effect. An 8×8-pixel image of a transparent circle surrounded by<br /> a black bezel, with a white highlight for a dash of style, is painted over the scaled-up<br /> color pixel. As an optimization, the bulbs are preassembled into an image that can be<br /> painted once for each column. Figure 31-2 shows what the bulb mask looks like blown<br /> up. The two white pixels are the highlight. The black pixels in the corner are opaque.<br /> Finally, all of the gray pixels in the middle are transparent, to allow the lightbulb color<br /> to show through.<br /> Lavatron paints so fast because it doesn’t have to repaint what it has already drawn.<br /> The technique of copying the area of the screen that’s good and painting just the portion<br /> that’s new is used in many common operations involving scrolling. The awt.Graphics<br /> function copyArea( ) takes a portion of an image defined by a rectangle and moves it<br /> by an x,y offset from its starting location. As a graphics speed optimization, copyArea( )<br /> is hard to beat. It consistently outperforms any other technique of image rendering,<br /> such as the use of drawImage( ), or drawImage( ) through a clipRect( ). Building an<br /> Figure 31-2.<br /> A blown-up light bulb image</div> <div>10 Java™ 2: The Complete Reference<br /> when you read your e-mail, you are viewing passive data. Even when you download a<br /> program, the program’s code is still only passive data until you execute it. However, a<br /> second type of object can be transmitted to your computer: a dynamic, self-executing<br /> program. Such a program is an active agent on the client computer, yet is initiated by<br /> the server. For example, a program might be provided by the server to display properly<br /> the data that the server is sending.<br /> As desirable as dynamic, networked programs are, they also present serious<br /> problems in the areas of security and portability. Prior to Java, cyberspace was<br /> effectively closed to half the entities that now live there. As you will see, Java addresses<br /> those concerns and, by doing so, has opened the door to an exciting new form of<br /> program: the applet.<br /> Java Applets and Applications<br /> Java can be used to create two types of programs: applications and applets. An<br /> application is a program that runs on your computer, under the operating system of that<br /> computer. That is, an application created by Java is more or less like one created using C<br /> or C++. When used to create applications, Java is not much different from any other<br /> computer language. Rather, it is Java’s ability to create applets that makes it important.<br /> An applet is an application designed to be transmitted over the Internet and executed by<br /> a Java-compatible Web browser. An applet is actually a tiny Java program, dynamically<br /> downloaded across the network, just like an image, sound file, or video clip. The<br /> important difference is that an applet is an intelligent program, not just an animation or<br /> media file. In other words, an applet is a program that can react to user input and<br /> dynamically change—not just run the same animation or sound over and over.<br /> As exciting as applets are, they would be nothing more than wishful thinking if<br /> Java were not able to address the two fundamental problems associated with them:<br /> security and portability. Before continuing, let’s define what these two terms mean<br /> relative to the Internet.<br /> Security<br /> As you are likely aware, every time that you download a “normal” program, you<br /> are risking a viral infection. Prior to Java, most users did not download executable<br /> programs frequently, and those who did scanned them for viruses prior to execution.<br /> Even so, most users still worried about the possibility of infecting their systems with<br /> a virus. In addition to viruses, another type of malicious program exists that must be<br /> guarded against. This type of program can gather private information, such as credit<br /> card numbers, bank account balances, and passwords, by searching the contents of<br /> your computer’s local file system. Java answers both of these concerns by providing<br /> a “firewall” between a networked application and your computer.<br /> When you use a Java-compatible Web browser, you can safely download Java<br /> applets without fear of viral infection or malicious intent. Java achieves this protection<br /> by confining a Java program to the Java execution environment and not allowing it</div> <div>THE JAVA LANGUAGE<br /> Chapter 8: Inheritance 199<br /> }<br /> // constructor used when all dimensions specified<br /> Box(double w, double h, double d) {<br /> width = w;<br /> height = h;<br /> depth = d;<br /> }<br /> // constructor used when no dimensions specified<br /> Box() {<br /> width = -1; // use -1 to indicate<br /> height = -1; // an uninitialized<br /> depth = -1; // box<br /> }<br /> // constructor used when cube is created<br /> Box(double len) {<br /> width = height = depth = len;<br /> }<br /> // compute and return volume<br /> double volume() {<br /> return width * height * depth;<br /> }<br /> // BoxWeight now fully implements all constructors.<br /> class BoxWeight extends Box {<br /> double weight; // weight of box<br /> // construct clone of an object<br /> BoxWeight(BoxWeight ob) { // pass object to constructor<br /> super(ob);<br /> weight = ob.weight;<br /> }<br /> // constructor when all parameters are specified<br /> BoxWeight(double w, double h, double d, double m) {<br /> super(w, h, d); // call superclass constructor<br /> weight = m;<br /> }</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 27: Servlets 967<br /> Method<br /> long getLastAccessedTime( )<br /> void invalidate( )<br /> boolean isNew( )<br /> void removeAttribute(String attr)<br /> void setAttribute(String attr, Object val)<br /> Description<br /> Returns the time (in milliseconds since<br /> midnight, January 1, 1970, GMT) when<br /> the client last made a request for this<br /> session.<br /> Invalidates this session and removes it<br /> from the context.<br /> Returns true if the server created the<br /> session and it has not yet been<br /> accessed by the client.<br /> Removes the attribute specified by attr<br /> from the session.<br /> Associates the value passed in val with<br /> the attribute name passed in attr.<br /> Table 27-7.<br /> The Methods Defined by HttpSession (continued)<br /> The HttpSessionBindingListener Interface<br /> The HttpSessionBindingListener interface is implemented by objects that need to be<br /> notified when they are bound to or unbound from an HTTP session. The methods that<br /> are invoked when an object is bound or unbound are<br /> void valueBound(HttpSessionBindingEvent e)<br /> void valueUnbound(HttpSessionBindingEvent e)<br /> Here, e is the event object that describes the binding.<br /> The Cookie Class<br /> The Cookie class encapsulates a cookie. A cookie is stored on a client and contains state<br /> information. Cookies are valuable for tracking user activities. For example, assume that<br /> a user visits an online store. A cookie can save the user’s name, address, and other<br /> information. The user does not need to enter this data each time he or she visits the store.<br /> A servlet can write a cookie to a user’s machine via the addCookie( ) method of the<br /> HttpServletResponse interface. The data for that cookie is then included in the header<br /> of the HTTP response that is sent to the browser.</div> <div>THE JAVA LANGUAGE<br /> Chapter 11: Multithreaded Programming 295<br /> This prevents other threads from entering call( ) while another thread is using it.<br /> After synchronized has been added to call( ), the output of the program is as follows:<br /> [Hello]<br /> [Synchronized]<br /> [World]<br /> Any time that you have a method, or group of methods, that manipulates the<br /> internal state of an object in a multithreaded situation, you should use the synchronized<br /> keyword to guard the state from race conditions. Remember, once a thread enters any<br /> synchronized method on an instance, no other thread can enter any other synchronized<br /> method on the same instance. However, nonsynchronized methods on that instance<br /> will continue to be callable.<br /> The synchronized Statement<br /> While creating synchronized methods within classes that you create is an easy and<br /> effective means of achieving synchronization, it will not work in all cases. To understand<br /> why, consider the following. Imagine that you want to synchronize access to objects of<br /> a class that was not designed for multithreaded access. That is, the class does not use<br /> synchronized methods. Further, this class was not created by you, but by a third party,<br /> and you do not have access to the source code. Thus, you can’t add synchronized to<br /> the appropriate methods within the class. How can access to an object of this class be<br /> synchronized? Fortunately, the solution to this problem is quite easy: You simply put<br /> calls to the methods defined by this class inside a synchronized block.<br /> This is the general form of the synchronized statement:<br /> synchronized(object) {<br /> // statements to be synchronized<br /> }<br /> Here, object is a reference to the object being synchronized. A synchronized block<br /> ensures that a call to a method that is a member of object occurs only after the current<br /> thread has successfully entered object’s monitor.<br /> Here is an alternative version of the preceding example, using a synchronized block<br /> within the run( ) method:<br /> // This program uses a synchronized block.<br /> class Callme {<br /> void call(String msg) {<br /> System.out.print("[" + msg);<br /> try {</div> <div>Contents<br /> Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .<br /> xxv<br /> Part I<br /> The Java Language<br /> 1 The Genesis of Java . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3<br /> Java’s Lineage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4<br /> The Birth of Modern Programming: C . . . . . . . . . . . . . . . . . . . . . . . 4<br /> The Need for C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6<br /> The Stage Is Set for Java . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7<br /> The Creation of Java . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7<br /> The C# Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9<br /> Why Java Is Important to the Internet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9<br /> Java Applets and Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10<br /> Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10<br /> Portability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11<br /> Java’s Magic: The Bytecode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11<br /> The Java Buzzwords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12<br /> Simple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13<br /> Object-Oriented . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13<br /> vii</div> <div>966 Java™ 2: The Complete Reference<br /> Method<br /> void setDateHeader(String field, long msec)<br /> void setHeader(String field, String value)<br /> void setIntHeader(String field, int value)<br /> void setStatus(int code)<br /> Description<br /> Adds field to the header with date<br /> value equal to msec (milliseconds<br /> since midnight, January 1, 1970,<br /> GMT).<br /> Adds field to the header with value<br /> equal to value.<br /> Adds field to the header with value<br /> equal to value.<br /> Sets the status code for this<br /> response to code.<br /> Table 27-6.<br /> Various Methods Defined by HttpServletResponse (continued)<br /> The HttpSession Interface<br /> The HttpSession interface is implemented by the server. It enables a servlet to read and<br /> write the state information that is associated with an HTTP session. Several of its methods<br /> are summarized in Table 27-7. All of these methods throw an IllegalStateException if the<br /> session has already been invalidated.<br /> Method<br /> Object getAttribute(String attr)<br /> Enumeration getAttributeNames( )<br /> long getCreationTime( )<br /> String getId( )<br /> Description<br /> Returns the value associated with the<br /> name passed in attr. Returns null if<br /> attr is not found.<br /> Returns an enumeration of the attribute<br /> names associated with the session.<br /> Returns the time (in milliseconds since<br /> midnight, January 1, 1970, GMT) when<br /> this session was created.<br /> Returns the session ID.<br /> Table 27-7.<br /> The Methods Defined by HttpSession</div> <div>878 Java™ 2: The Complete Reference<br /> In the first line, the name of the server is provided. The second line uses its IP address<br /> (11.12.13.14).<br /> You can try this example without actually having a remote server. To do so, simply<br /> install all of the programs on the same machine, start rmiregistry, start AddSever, and<br /> then execute AddClient using this command line:<br /> java AddClient 127.0.0.1 8 9<br /> Here, the address 127.0.0.1 is the “loop back” address for the local machine. Using this<br /> address allows you to exercise the entire RMI mechanism without actually having to<br /> install the server on a remote computer.<br /> In either case, sample output from this program is shown here:<br /> The first number is: 8<br /> The second number is: 9<br /> The sum is: 17.0<br /> Text Formatting<br /> The package java.text allows you to format, search, and manipulate text. This section<br /> takes a brief look at its most commonly used classes: those that format date and time<br /> information.<br /> DateFormat Class<br /> DateFormat is an abstract class that provides the ability to format and parse dates and<br /> times. The getDateInstance( ) method returns an instance of DateFormat that can<br /> format date information. It is available in these forms:<br /> static final DateFormat getDateInstance( )<br /> static final DateFormat getDateInstance(int style)<br /> static final DateFormat getDateInstance(int style, Locale locale)<br /> The argument style is one of the following values: DEFAULT, SHORT, MEDIUM,<br /> LONG, or FULL. These are int constants defined by DateFormat. They cause different<br /> details about the date to be presented. The argument locale is one of the static references<br /> defined by Locale (refer to Chapter 16 for details). If the style and/or locale is not<br /> specified, defaults are used.<br /> One of the most commonly used methods in this class is format( ). It has several<br /> overloaded forms, one of which is shown here:<br /> final String format(Date d)</div> <div>1048 Java™ 2: The Complete Reference<br /> The ImageMenu applet is a simple program that presents an image-based menu<br /> with an arbitrary number of choices in a vertical list. When the user moves the<br /> mouse cursor over these choices, the one under the cursor changes appearance,<br /> indicating that it can be clicked on. When the user clicks on a choice, the web browser<br /> changes to a new document specified for that choice. ImageMenu was created by<br /> David LaVallée, the creator of several interesting applets. Figure 30-1 shows an<br /> instance of ImageMenu.<br /> ImageMenu uses the showDocument( ) function in AppletContext to make the<br /> hypertext leap to the new pages. The novelty of ImageMenu is that it uses different<br /> portions of a single source image to draw the menu on the screen. Basing a menu on<br /> an image rather than on text frees you to design menus that use any font or image you<br /> desire. You can also provide various types of selection feedback. You no longer need to<br /> rely on the AWT’s limited rendering functions.<br /> Figure 30-1.<br /> An example of ImageMenu</div> <div>1018 Java™ 2: The Complete Reference<br /> String link_target_frame;<br /> boolean stopFlag;<br /> public void init() {<br /> String s = getParameter("bgcolor");<br /> if(s != null) {<br /> Color color = new Color(Integer.parseInt(s.substring(1), 16));<br /> setBackground(color);<br /> getParent().setBackground(color);<br /> getParent().repaint();<br /> }<br /> billboards = new<br /> BillData[Integer.parseInt(getParameter("billboards"))];<br /> current_billboard = next_billboard<br /> = (int)(Math.random() *billboards.length);<br /> parseBillData();<br /> }<br /> void parseBillData() {<br /> String s = getParameter("bill" + next_billboard);<br /> int field_end = s.indexOf(",");<br /> Image new_image = getImage(getDocumentBase(),<br /> s.substring(0, field_end));<br /> URL link;<br /> try {<br /> link = new URL(getDocumentBase(),<br /> s.substring(field_end + 1));<br /> }<br /> catch (java.net.MalformedURLException e) {<br /> e.printStackTrace();<br /> link = getDocumentBase();<br /> }<br /> billboards[next_billboard] = new BillData(link, new_image);<br /> if(image == null) {<br /> image = new_image;<br /> }<br /> else {<br /> prepareImage(new_image, this);<br /> billboards[next_billboard].initPixels(getSize().width,<br /> getSize().height);<br /> }</div> <div>1002 Java™ 2: The Complete Reference<br /> Notice that House multiply inherits Foundation, Walls, and Rooms. While there is<br /> nothing wrong with structuring a C++ hierarchy like this, it is not necessary. For<br /> example, here is the same set of classes structured for Java:<br /> class Foundation {<br /> // ...<br /> }<br /> class Walls extends Foundation {<br /> // ...<br /> }<br /> class Rooms extends Walls {<br /> // ...<br /> }<br /> class House extends Rooms {<br /> // ...<br /> }<br /> Here, each class extends the preceding one, with House becoming the final extension.<br /> Sometimes a multiple inheritance hierarchy is more readily converted by including<br /> objects of the multiply inherited classes in the final object. For example, here is another<br /> way that House could be constructed in Java:<br /> class Foundation {<br /> // ...<br /> }<br /> class Walls{<br /> // ...<br /> }<br /> class Rooms {<br /> // ...<br /> }<br /> /* Now, House includes Foundation, Walls, and Rooms<br /> as object members.<br /> */</div> <div>612 Java™ 2: The Complete Reference<br /> private String docRoot;<br /> private LogMessage log;<br /> private Hashtable cache = new Hashtable();<br /> private boolean stopFlag;<br /> private static String version = "1.0";<br /> private static String mime_text_html = "text/html";<br /> private static String CRLF = "\r\n";<br /> private static String indexfile = "index.html";<br /> private static int buffer_size = 8192;<br /> static String mt[] = { // mapping from file ext to Mime-Type<br /> "txt", "text/plain",<br /> "html", mime_text_html,<br /> "htm", "text/html",<br /> "gif", "image/gif",<br /> "jpg", "image/jpg",<br /> "jpeg", "image/jpg",<br /> "class", "application/octet-stream"<br /> };<br /> static String defaultExt = "txt";<br /> static Hashtable types = new Hashtable();<br /> static {<br /> for (int i=0; i<mt.length;i+=2)<br /> types.put(mt[i], mt[i+1]);<br /> }<br /> static String fnameToMimeType(String filename) {<br /> if (filename.endsWith("/")) // special for index files.<br /> return mime_text_html;<br /> int dot = filename.lastIndexOf('.');<br /> String ext = (dot > 0) ? filename.substring(dot + 1) : defaultExt;<br /> String ret = (String) types.get(ext);<br /> return ret != null ? ret : (String)types.get(defaultExt);<br /> }<br /> int hits_served = 0;<br /> int bytes_served = 0;<br /> int files_in_cache = 0;<br /> int bytes_in_cache = 0;<br /> int hits_to_cache = 0;</div> <div>332 Java™ 2: The Complete Reference<br /> int b; // will persist<br /> }<br /> Here, if an object of type T is written to a persistent storage area, the contents of a<br /> would not be saved, but the contents of b would.<br /> The volatile modifier tells the compiler that the variable modified by volatile can<br /> be changed unexpectedly by other parts of your program. One of these situations<br /> involves multithreaded programs. (You saw an example of this in Chapter 11.) In a<br /> multithreaded program, sometimes, two or more threads share the same instance<br /> variable. For efficiency considerations, each thread can keep its own, private copy of<br /> such a shared variable. The real (or master) copy of the variable is updated at various<br /> times, such as when a synchronized method is entered. While this approach works<br /> fine, it may be inefficient at times. In some cases, all that really matters is that the<br /> master copy of a variable always reflects its current state. To ensure this, simply specify<br /> the variable as volatile, which tells the compiler that it must always use the master<br /> copy of a volatile variable (or, at least, always keep any private copies up to date with<br /> the master copy, and vice versa). Also, accesses to the master variable must be executed<br /> in the precise order in which they are executed on any private copy.<br /> volatile in Java has, more or less, the same meaning that it has in C/C++/C#.<br /> Using instanceof<br /> Sometimes, knowing the type of an object during run time is useful. For example, you<br /> might have one thread of execution that generates various types of objects, and another<br /> thread that processes these objects. In this situation, it might be useful for the processing<br /> thread to know the type of each object when it receives it. Another situation in which<br /> knowledge of an object’s type at run time is important involves casting. In Java, an<br /> invalid cast causes a run-time error. Many invalid casts can be caught at compile time.<br /> However, casts involving class hierarchies can produce invalid casts that can be detected<br /> only at run time. For example, a superclass called A can produce two subclasses, called B<br /> and C. Thus, castingaBobject into type A or castingaCobject into type A is legal, but<br /> castingaBobject into type C (or vice versa) isn’t legal. Because an object of type A can<br /> refer to objects of either B or C, how can you know, at run time, what type of object is<br /> actually being referred to before attempting the cast to type C? It could be an object of<br /> type A, B, or C. If it is an object of type B, a run-time exception will be thrown. Java<br /> provides the run-time operator instanceof to answer this question.<br /> The instanceof operator has this general form:<br /> object instanceof type</div> <div>1074 Java™ 2: The Complete Reference<br /> Scoring<br /> Scores are assessed at the end of each turn. Each tile has a small number engraved on<br /> its face next to the letter. This score may be multiplied by two or three, depending on<br /> the value (color) of the square on which it was placed. The entire sum for a word may<br /> also be multiplied by two or three if any letter in the word covers the appropriate<br /> square. If a word comes in contact with any other tiles to form additional words, they<br /> are counted separately. If a player uses all seven tiles in a single turn, an additional 50<br /> points are awarded. At the end of the game, the player with the highest score wins.<br /> Figure 32-5 shows an example of a board after a few turns have been taken. Patrick<br /> started with SIRE, worth eight points. That came from the four one-point tiles and the<br /> double-word score on the center tile. Next, Herb played HIRE, using the I from SIRE.<br /> This was worth seven points, the sum of the four tiles involved. Notice that Herb got<br /> credit for reusing Patrick’s I but not the double-word score underneath it. At the point<br /> shown in Figure 32-5, Patrick has played GREAT and is about to click the Done button<br /> to complete his turn. Notice that the tiles in play are brighter than those that have<br /> already been played (see Figure 32-6).<br /> At any time during play, the players may converse by typing in the text entry area<br /> at the top of the applet (see Figure 32-7). These messages will appear one at a time in<br /> the other player’s browser’s status line, typically at the bottom of the browser (see<br /> Figure 32-8).<br /> Figure 32-5.<br /> Scrabblet early in a game</div> <div>THE JAVA LIBRARY<br /> Chapter 20: Event Handling 667<br /> Here, src is a reference to the object that generated this event. The type of the event is<br /> specified by type.<br /> The TextEvent object does not include the characters currently in the text component<br /> that generated the event. Instead, your program must use other methods associated with<br /> the text component to retrieve that information. This operation differs from other event<br /> objects discussed in this section. For this reason, no methods are discussed here for the<br /> TextEvent class. Think of a text event notification as a signal to a listener that it should<br /> retrieve information from a specific text component.<br /> The WindowEvent Class<br /> There are ten types of window events. The WindowEvent class defines integer<br /> constants that can be used to identify them. The constants and their meanings are<br /> shown here:<br /> WINDOW_ACTIVATED<br /> WINDOW_CLOSED<br /> WINDOW_CLOSING<br /> WINDOW_DEACTIVATED<br /> WINDOW_DEICONIFIED<br /> WINDOW_GAINED_FOCUS<br /> WINDOW_ICONIFIED<br /> WINDOW_LOST_FOCUS<br /> WINDOW_OPENED<br /> WINDOW_STATE_CHANGED<br /> The window was activated.<br /> The window has been closed.<br /> The user requested that the window<br /> be closed.<br /> The window was deactivated.<br /> The window was deiconified.<br /> The window gained input focus.<br /> The window was iconified.<br /> The window lost input focus.<br /> The window was opened.<br /> The state of the window changed.<br /> (Added by Java 2, version 1.4.)<br /> WindowEvent is a subclass of ComponentEvent. It defines several constructors.<br /> The first is<br /> WindowEvent(Window src, int type)<br /> Here, src is a reference to the object that generated this event. The type of the event is type.<br /> Java 2, version 1.4 adds the next three constructors.<br /> WindowEvent(Window src, int type, Window other)<br /> WindowEvent(Window src, int type, int fromState, int toState)<br /> WindowEvent(Window src, int type, Window other, int fromState, int toState)</div> <div>THE JAVA LIBRARY<br /> Chapter 24: New I/O, Regular Expressions, and Other Packages 865<br /> As the output shows, the regular expression pattern “W+” matches any arbitrarily long<br /> sequence of Ws.<br /> The next program uses a wildcard to create a pattern that will match any sequence<br /> that begins with e and ends with d. To do this, it uses the dot wildcard character along<br /> with the + quantifier.<br /> // Use wildcard and quantifier.<br /> import java.util.regex.*;<br /> class RegExpr5 {<br /> public static void main(String args[]) {<br /> Pattern pat = Pattern.compile("e.+d");<br /> Matcher mat = pat.matcher("extend cup end table");<br /> }<br /> }<br /> while(mat.find())<br /> System.out.println("Match: " + mat.group());<br /> You might be surprised by the the output produced by the program, which is<br /> shown here:<br /> Match: extend cup end<br /> Only one match is found, and it is the longest sequence that begins with e and ends<br /> with d. You might have expected two matches: extend and end. The reason that the<br /> longer sequence is found is that by default, find( ) matches the longest sequence that<br /> fits the pattern. This is called greedy behavior. You can specify reluctant behavior by adding<br /> the ? quantifier to the pattern, as shown in this version of the program. It causes the<br /> shortest matching pattern to be obtained.<br /> // Use the ? quantifier.<br /> import java.util.regex.*;<br /> class RegExpr6 {<br /> public static void main(String args[]) {<br /> // Use reluctant matching behavior.<br /> Pattern pat = Pattern.compile("e.+?d");<br /> Matcher mat = pat.matcher("extend cup end table");<br /> while(mat.find())</div> <div>THE JAVA LIBRARY<br /> Chapter 20: Event Handling 659<br /> int getModifiers( )<br /> Java 2, version 1.4 added the method getWhen( ) that returns the time at which the event<br /> took place. This is called the event’s timestamp. The getWhen( ) method is shown here.<br /> long getWhen( )<br /> Timestamps were added by ActionEvent to help support the improved input focus<br /> subsystem implemented by Java 2, version 1.4.<br /> The AdjustmentEvent Class<br /> An AdjustmentEvent is generated by a scroll bar. There are five types of adjustment<br /> events. The AdjustmentEvent class defines integer constants that can be used to identify<br /> them. The constants and their meanings are shown here:<br /> BLOCK_DECREMENT<br /> BLOCK_INCREMENT<br /> TRACK<br /> UNIT_DECREMENT<br /> UNIT_INCREMENT<br /> The user clicked inside the scroll bar to decrease<br /> its value.<br /> The user clicked inside the scroll bar to increase<br /> its value.<br /> The slider was dragged.<br /> The button at the end of the scroll bar was clicked<br /> to decrease its value.<br /> The button at the end of the scroll bar was clicked<br /> to increase its value.<br /> In addition, there is an integer constant, ADJUSTMENT_VALUE_CHANGED,<br /> that indicates that a change has occurred.<br /> Here is one AdjustmentEvent constructor:<br /> AdjustmentEvent(Adjustable src, int id, int type, int data)<br /> Here, src is a reference to the object that generated this event. The id equals<br /> ADJUSTMENT_VALUE_CHANGED. The type of the event is specified by type,<br /> and its associated data is data.<br /> The getAdjustable( ) method returns the object that generated the event. Its form<br /> is shown here:<br /> Adjustable getAdjustable( )<br /> The type of the adjustment event may be obtained by the getAdjustmentType( ) method.<br /> It returns one of the constants defined by AdjustmentEvent. The general form is<br /> shown here:<br /> int getAdjustmentType( )</div> <div>THE JAVA LIBRARY<br /> Chapter 21: Introducing the AWT: Working with Windows, Graphics, and Text 727<br /> curX = fm.stringWidth(s); // advance to end of line<br /> }<br /> // Display on same line.<br /> void sameLine(String s, Graphics g) {<br /> FontMetrics fm = g.getFontMetrics();<br /> }<br /> }<br /> g.drawString(s, curX, curY);<br /> curX += fm.stringWidth(s); // advance to end of line<br /> Sample output from this program is shown here:<br /> Centering Text<br /> Here is an example that centers text, left to right, top to bottom, in a window. It obtains<br /> the ascent, descent, and width of the string and computes the position at which it must<br /> be displayed to be centered.<br /> // Center text.<br /> import java.applet.*;<br /> import java.awt.*;<br /> /*<br /> <applet code="CenterText" width=200 height=100><br /> </applet><br /> */<br /> public class CenterText extends Applet {<br /> final Font f = new Font("SansSerif", Font.BOLD, 18);<br /> public void paint(Graphics g) {</div> <div>116 Java™ 2: The Complete Reference<br /> public static void main(String args[]) {<br /> int num;<br /> boolean isPrime = true;<br /> }<br /> }<br /> num = 14;<br /> for(int i=2; i <= num/2; i++) {<br /> if((num % i) == 0) {<br /> isPrime = false;<br /> break;<br /> }<br /> }<br /> if(isPrime) System.out.println("Prime");<br /> else System.out.println("Not Prime");<br /> Using the Comma<br /> There will be times when you will want to include more than one statement in the<br /> initialization and iteration portions of the for loop. For example, consider the loop<br /> in the following program:<br /> class Sample {<br /> public static void main(String args[]) {<br /> int a, b;<br /> }<br /> }<br /> b = 4;<br /> for(a=1; a<b; a++) {<br /> System.out.println("a = " + a);<br /> System.out.println("b = " + b);<br /> b--;<br /> }<br /> As you can see, the loop is controlled by the interaction of two variables. Since the loop<br /> is governed by two variables, it would be useful if both could be included in the for<br /> statement, itself, instead of b being handled manually. Fortunately, Java provides a way<br /> to accomplish this. To allow two or more variables to control a for loop, Java permits<br /> you to include multiple statements in both the initialization and iteration portions of<br /> the for. Each statement is separated from the next by a comma.</div> <div>74 Java™ 2: The Complete Reference<br /> Java provides a rich operator environment. Most of its operators can be divided<br /> into the following four groups: arithmetic, bitwise, relational, and logical. Java also<br /> defines some additional operators that handle certain special situations. This chapter<br /> describes all of Java’s operators except for the type comparison operator instanceof,<br /> which is examined in Chapter 12.<br /> If you are familiar with C/C++/C#, then you will be pleased to know that most operators<br /> in Java work just like they do in those languages. However, there are some subtle differences,<br /> so a careful reading is advised.<br /> Arithmetic Operators<br /> Arithmetic operators are used in mathematical expressions in the same way that they<br /> are used in algebra. The following table lists the arithmetic operators:<br /> Operator<br /> Result<br /> + Addition<br /> – Subtraction (also unary minus)<br /> * Multiplication<br /> / Division<br /> % Modulus<br /> ++ Increment<br /> += Addition assignment<br /> –= Subtraction assignment<br /> *= Multiplication assignment<br /> /= Division assignment<br /> %= Modulus assignment<br /> – – Decrement<br /> The operands of the arithmetic operators must be of a numeric type. You cannot<br /> use them on boolean types, but you can use them on char types, since the char type in<br /> Java is, essentially, a subset of int.<br /> The Basic Arithmetic Operators<br /> The basic arithmetic operations—addition, subtraction, multiplication, and division—<br /> all behave as you would expect for all numeric types. The minus operator also has<br /> a unary form which negates its single operand. Remember that when the division</div> <div>THE JAVA LANGUAGE<br /> Chapter 7: A Closer Look at Methods and Classes 171<br /> you can watch what is going on and abort execution if you see that you have made<br /> a mistake.<br /> Here is one more example of recursion. The recursive method printArray( ) prints<br /> the first i elements in the array values.<br /> // Another example that uses recursion.<br /> class RecTest {<br /> int values[];<br /> }<br /> RecTest(int i) {<br /> values = new int[i];<br /> }<br /> // display array -- recursively<br /> void printArray(int i) {<br /> if(i==0) return;<br /> else printArray(i-1);<br /> System.out.println("[" + (i-1) + "] " + values[i-1]);<br /> }<br /> class Recursion2 {<br /> public static void main(String args[]) {<br /> RecTest ob = new RecTest(10);<br /> int i;<br /> for(i=0; i<10; i++) ob.values[i] = i;<br /> }<br /> }<br /> ob.printArray(10);<br /> This program generates the following output:<br /> [0] 0<br /> [1] 1<br /> [2] 2<br /> [3] 3<br /> [4] 4<br /> [5] 5<br /> [6] 6</div> <div>THE JAVA LIBRARY<br /> Chapter 21: Introducing the AWT: Working with Windows, Graphics, and Text 715<br /> g.drawLine(0, 100, 100, 0);<br /> g.setColor(c2);<br /> g.drawLine(40, 25, 250, 180);<br /> g.drawLine(75, 90, 400, 400);<br /> g.setColor(c3);<br /> g.drawLine(20, 150, 400, 40);<br /> g.drawLine(5, 290, 80, 19);<br /> g.setColor(Color.red);<br /> g.drawOval(10, 10, 50, 50);<br /> g.fillOval(70, 90, 140, 100);<br /> g.setColor(Color.blue);<br /> g.drawOval(190, 10, 90, 30);<br /> g.drawRect(10, 10, 60, 50);<br /> }<br /> }<br /> g.setColor(Color.cyan);<br /> g.fillRect(100, 10, 60, 50);<br /> g.drawRoundRect(190, 10, 60, 50, 15, 15);<br /> Setting the Paint Mode<br /> The paint mode determines how objects are drawn in a window. By default, new output<br /> to a window overwrites any preexisting contents. However, it is possible to have new<br /> objects XORed onto the window by using setXORMode( ), as follows:<br /> void setXORMode(Color xorColor)<br /> Here, xorColor specifies the color that will be XORed to the window when an object is<br /> drawn. The advantage of XOR mode is that the new object is always guaranteed to be<br /> visible no matter what color the object is drawn over.<br /> To return to overwrite mode, call setPaintMode( ), shown here:<br /> void setPaintMode( )<br /> In general, you will want to use overwrite mode for normal output, and XOR mode for<br /> special purposes. For example, the following program displays cross hairs that track<br /> the mouse pointer. The cross hairs are XORed onto the window and are always visible,<br /> no matter what the underlying color is.</div> <div>714 Java™ 2: The Complete Reference<br /> Each of these methods returns the RGB color component found in the invoking Color<br /> object in the lower 8 bits of an integer.<br /> getRGB( )<br /> To obtain a packed, RGB representation of a color, use getRGB( ), shown here:<br /> int getRGB( )<br /> The return value is organized as described earlier.<br /> Setting the Current Graphics Color<br /> By default, graphics objects are drawn in the current foreground color. You can change<br /> this color by calling the Graphics method setColor( ):<br /> void setColor(Color newColor)<br /> Here, newColor specifies the new drawing color.<br /> You can obtain the current color by calling getColor( ), shown here:<br /> Color getColor( )<br /> A Color Demonstration Applet<br /> The following applet constructs several colors and draws various objects using<br /> these colors:<br /> // Demonstrate color.<br /> import java.awt.*;<br /> import java.applet.*;<br /> /*<br /> <applet code="ColorDemo" width=300 height=200><br /> </applet><br /> */<br /> public class ColorDemo extends Applet {<br /> // draw lines<br /> public void paint(Graphics g) {<br /> Color c1 = new Color(255, 100, 100);<br /> Color c2 = new Color(100, 255, 100);<br /> Color c3 = new Color(100, 100, 255);<br /> g.setColor(c1);<br /> g.drawLine(0, 0, 100, 100);</div> <div>650 Java™ 2: The Complete Reference<br /> AppletContext is an interface that lets you get information from the applet’s execution<br /> environment. The methods defined by AppletContext are shown in Table 19-2. The<br /> context of the currently executing applet is obtained by a call to the getAppletContext( )<br /> method defined by Applet.<br /> Within an applet, once you have obtained the applet’s context, you can bring<br /> another document into view by calling showDocument( ). This method has no<br /> return value and throws no exception if it fails, so use it carefully. There are two<br /> showDocument( ) methods. The method showDocument(URL) displays the document<br /> Method<br /> Applet getApplet(String appletName)<br /> Enumeration getApplets( )<br /> AudioClip getAudioClip(URL url)<br /> Image getImage(URL url)<br /> InputStream getStream(String key)<br /> Iterator getStreamKeys( )<br /> void setStream(String key,<br /> InputStream strm)<br /> void showDocument(URL url)<br /> void showDocument(URL url,<br /> String where)<br /> void showStatus(String str)<br /> Description<br /> Returns the applet specified by appletName if it is<br /> within the current applet context. Otherwise, null<br /> is returned.<br /> Returns an enumeration that contains all of the<br /> applets within the current applet context.<br /> Returns an AudioClip object that encapsulates the<br /> audio clip found at the location specified by url.<br /> Returns an Image object that encapsulates the image<br /> found at the location specified by url.<br /> Returns the stream linked to key. Keys are linked to<br /> streams by using the setStream( ) method. A null<br /> reference is returned if no stream is linked to key.<br /> (Added by Java 2, version 1.4)<br /> Returns an iterator for the keys associated with the<br /> invoking object. The keys are linked to streams. See<br /> getStream( ) and setStream( ). (Added by Java 2,<br /> version 1.4)<br /> Links the stream specified by strm to the key passed<br /> in key. The key is deleted from the invoking object if<br /> strm is null. (Added by Java 2, version 1.4)<br /> Brings the document at the URL specified by url<br /> into view. This method may not be supported by<br /> applet viewers.<br /> Brings the document at the URL specified by url<br /> into view. This method may not be supported by<br /> applet viewers. The placement of the document<br /> is specified by where as described in the text.<br /> Displays str in the status window.<br /> Table 19-2.<br /> The Abstract Methods Defined by the AppletContext Interface</div> <div>442 Java™ 2: The Complete Reference<br /> In addition to collections, the framework defines several map interfaces and classes.<br /> Maps store key/value pairs. Although maps are not “collections” in the proper use of<br /> the term, they are fully integrated with collections. In the language of the collections<br /> framework, you can obtain a collection-view of a map. Such a view contains the elements<br /> from the map stored in a collection. Thus, you can process the contents of a map as a<br /> collection, if you choose.<br /> The collection mechanism was retrofitted to some of the original classes defined by<br /> java.util so that they too could be integrated into the new system. It is important to<br /> understand that although the addition of collections altered the architecture of many<br /> of the original utility classes, it did not cause the deprecation of any. Collections simply<br /> provide a better way of doing several things.<br /> One last thing: If you are familiar with C++, then you will find it helpful to know<br /> that the Java collections technology is similar in spirit to the Standard Template Library<br /> (STL) defined by C++. What C++ calls a container, Java calls a collection.<br /> The Collection Interfaces<br /> The collections framework defines several interfaces. This section provides an overview of<br /> each interface. Beginning with the collection interfaces is necessary because they determine<br /> the fundamental nature of the collection classes. Put differently, the concrete classes simply<br /> provide different implementations of the standard interfaces. The interfaces that underpin<br /> collections are summarized in the following table:<br /> Interface<br /> Collection<br /> List<br /> Set<br /> SortedSet<br /> Description<br /> Enables you to work with groups of objects; it is at the top of the<br /> collections hierarchy<br /> Extends Collection to handle sequences (lists of objects)<br /> Extends Collection to handle sets, which must contain unique elements<br /> Extends Set to handle sorted sets<br /> In addition to the collection interfaces, collections also use the Comparator, Iterator,<br /> ListIterator and RandomAccess interfaces, which are described in depth later in this<br /> chapter. Briefly, Comparator defines how two objects are compared; Iterator and<br /> ListIterator enumerate the objects within a collection. By implementing RandomAccess,<br /> a list indicates that it supports efficient, random access to its elements.<br /> To provide the greatest flexibility in their use, the collection interfaces allow some<br /> methods to be optional. The optional methods enable you to modify the contents of a<br /> collection. Collections that support these methods are called modifiable. Collections that<br /> do not allow their contents to be changed are called unmodifiable. If an attempt is made</div> <div>968 Java™ 2: The Complete Reference<br /> The names and values of cookies are stored on the user’s machine. Some of the<br /> information that is saved for each cookie includes the following:<br /> ■ The name of the cookie<br /> ■ The value of the cookie<br /> ■ The expiration date of the cookie<br /> ■ The domain and path of the cookie<br /> The expiration date determines when this cookie is deleted from the user’s machine.<br /> If an expiration date is not explicitly assigned to a cookie, it is deleted when the current<br /> browser session ends. Otherwise, the cookie is saved in a file on the user’s machine.<br /> The domain and path of the cookie determine when it is included in the header of<br /> an HTTP request. If the user enters a URL whose domain and path match these values,<br /> the cookie is then supplied to the Web server. Otherwise, it is not.<br /> There is one constructor for Cookie. It has the signature shown here:<br /> Cookie(String name, String value)<br /> Here, the name and value of the cookie are supplied as arguments to the constructor.<br /> The methods of the Cookie class are summarized in Table 27-8.<br /> Method<br /> Object clone( )<br /> String getComment( )<br /> String getDomain( )<br /> int getMaxAge( )<br /> String getName( )<br /> String getPath( )<br /> boolean getSecure( )<br /> String getValue( )<br /> int getVersion( )<br /> Description<br /> Returns a copy of this object.<br /> Returns the comment.<br /> Returns the domain.<br /> Returns the age (in seconds).<br /> Returns the name.<br /> Returns the path.<br /> Returns true if the cookie must be sent using<br /> only a secure protocol. Otherwise, returns false.<br /> Returns the value.<br /> Returns the cookie protocol version. (Will be<br /> 0 or 1.)<br /> Table 27-8.<br /> The Methods Defined by Cookie</div> <div>THE JAVA LANGUAGE<br /> Chapter 11: Multithreaded Programming 291<br /> class HiLoPri {<br /> public static void main(String args[]) {<br /> Thread.currentThread().setPriority(Thread.MAX_PRIORITY);<br /> clicker hi = new clicker(Thread.NORM_PRIORITY + 2);<br /> clicker lo = new clicker(Thread.NORM_PRIORITY - 2);<br /> lo.start();<br /> hi.start();<br /> try {<br /> Thread.sleep(10000);<br /> } catch (InterruptedException e) {<br /> System.out.println("Main thread interrupted.");<br /> }<br /> lo.stop();<br /> hi.stop();<br /> // Wait for child threads to terminate.<br /> try {<br /> hi.t.join();<br /> lo.t.join();<br /> } catch (InterruptedException e) {<br /> System.out.println("InterruptedException caught");<br /> }<br /> }<br /> }<br /> System.out.println("Low-priority thread: " + lo.click);<br /> System.out.println("High-priority thread: " + hi.click);<br /> The output of this program, shown as follows when run under Windows 98,<br /> indicates that the threads did context switch, even though neither voluntarily yielded<br /> the CPU nor blocked for I/O. The higher-priority thread got approximately 90 percent<br /> of the CPU time.<br /> Low-priority thread: 4408112<br /> High-priority thread: 589626904<br /> Of course, the exact output produced by this program depends on the speed of your<br /> CPU and the number of other tasks running in the system. When this same program<br /> is run under a nonpreemptive system, different results will be obtained.<br /> One other note about the preceding program. Notice that running is preceded<br /> by the keyword volatile. Although volatile is examined more carefully in the next</div> <div>786 Java™ 2: The Complete Reference<br /> }<br /> g.drawString("Testing is off.", 10, 240);<br /> }<br /> class MyWindowAdapter extends WindowAdapter {<br /> MenuFrame menuFrame;<br /> public MyWindowAdapter(MenuFrame menuFrame) {<br /> this.menuFrame = menuFrame;<br /> }<br /> public void windowClosing(WindowEvent we) {<br /> menuFrame.dispose();<br /> }<br /> }<br /> class MyMenuHandler implements ActionListener, ItemListener {<br /> MenuFrame menuFrame;<br /> public MyMenuHandler(MenuFrame menuFrame) {<br /> this.menuFrame = menuFrame;<br /> }<br /> // Handle action events<br /> public void actionPerformed(ActionEvent ae) {<br /> String msg = "You selected ";<br /> String arg = (String)ae.getActionCommand();<br /> // Activate a dialog box when New is selected.<br /> if(arg.equals("New...")) {<br /> msg += "New.";<br /> SampleDialog d = new<br /> SampleDialog(menuFrame, "New Dialog Box");<br /> d.setVisible(true);<br /> }<br /> // Try defining other dialog boxes for these options.<br /> else if(arg.equals("Open..."))<br /> msg += "Open.";<br /> else if(arg.equals("Close"))<br /> msg += "Close.";<br /> else if(arg.equals("Quit..."))<br /> msg += "Quit.";<br /> else if(arg.equals("Edit"))<br /> msg += "Edit.";<br /> else if(arg.equals("Cut"))<br /> msg += "Cut.";</div> <div>THE JAVA LIBRARY<br /> Chapter 22: Using AWT Controls, Layout Managers, and Menus 761<br /> Figure 22-7.<br /> Sample output from the TextFieldDemo applet<br /> Using a TextArea<br /> Sometimes a single line of text input is not enough for a given task. To handle these<br /> situations, the AWT includes a simple multiline editor called TextArea. Following are<br /> the constructors for TextArea:<br /> TextArea( )<br /> TextArea(int numLines, int numChars)<br /> TextArea(String str)<br /> TextArea(String str, int numLines, int numChars)<br /> TextArea(String str, int numLines, int numChars, int sBars)<br /> Here, numLines specifies the height, in lines, of the text area, and numChars specifies its<br /> width, in characters. Initial text can be specified by str. In the fifth form you can specify<br /> the scroll bars that you want the control to have. sBars must be one of these values:<br /> SCROLLBARS_BOTH<br /> SCROLLBARS_HORIZONTAL_ONLY<br /> SCROLLBARS_NONE<br /> SCROLLBARS_VERTICAL_ONLY<br /> TextArea is a subclass of TextComponent. Therefore, it supports the getText( ), setText( ),<br /> getSelectedText( ), select( ), isEditable( ), and setEditable( ) methods described in the<br /> preceding section.</div> <div>This page intentionally left blank.</div> <div>520 Java™ 2: The Complete Reference<br /> class GregorianCalendarDemo {<br /> public static void main(String args[]) {<br /> String months[] = {<br /> "Jan", "Feb", "Mar", "Apr",<br /> "May", "Jun", "Jul", "Aug",<br /> "Sep", "Oct", "Nov", "Dec"};<br /> int year;<br /> // Create a Gregorian calendar initialized<br /> // with the current date and time in the<br /> // default locale and timezone.<br /> GregorianCalendar gcalendar = new GregorianCalendar();<br /> // Display current time and date information.<br /> System.out.print("Date: ");<br /> System.out.print(months[gcalendar.get(Calendar.MONTH)]);<br /> System.out.print(" " + gcalendar.get(Calendar.DATE) + " ");<br /> System.out.println(year = gcalendar.get(Calendar.YEAR));<br /> System.out.print("Time: ");<br /> System.out.print(gcalendar.get(Calendar.HOUR) + ":");<br /> System.out.print(gcalendar.get(Calendar.MINUTE) + ":");<br /> System.out.println(gcalendar.get(Calendar.SECOND));<br /> }<br /> }<br /> // Test if the current year is a leap year<br /> if(gcalendar.isLeapYear(year)) {<br /> System.out.println("The current year is a leap year");<br /> }<br /> else {<br /> System.out.println("The current year is not a leap year");<br /> }<br /> Sample output is shown here:<br /> Date: Apr 22 2002<br /> Time: 11:25:27<br /> The current year is not a leap year</div> <div>518 Java™ 2: The Complete Reference<br /> class CalendarDemo {<br /> public static void main(String args[]) {<br /> String months[] = {<br /> "Jan", "Feb", "Mar", "Apr",<br /> "May", "Jun", "Jul", "Aug",<br /> "Sep", "Oct", "Nov", "Dec"};<br /> // Create a calendar initialized with the<br /> // current date and time in the default<br /> // locale and timezone.<br /> Calendar calendar = Calendar.getInstance();<br /> // Display current time and date information.<br /> System.out.print("Date: ");<br /> System.out.print(months[calendar.get(Calendar.MONTH)]);<br /> System.out.print(" " + calendar.get(Calendar.DATE) + " ");<br /> System.out.println(calendar.get(Calendar.YEAR));<br /> System.out.print("Time: ");<br /> System.out.print(calendar.get(Calendar.HOUR) + ":");<br /> System.out.print(calendar.get(Calendar.MINUTE) + ":");<br /> System.out.println(calendar.get(Calendar.SECOND));<br /> // Set the time and date information and display it.<br /> calendar.set(Calendar.HOUR, 10);<br /> calendar.set(Calendar.MINUTE, 29);<br /> calendar.set(Calendar.SECOND, 22);<br /> }<br /> }<br /> System.out.print("Updated time: ");<br /> System.out.print(calendar.get(Calendar.HOUR) + ":");<br /> System.out.print(calendar.get(Calendar.MINUTE) + ":");<br /> System.out.println(calendar.get(Calendar.SECOND));<br /> Sample output is shown here:<br /> Date: Apr 22 2002<br /> Time: 11:24:25<br /> Updated time: 10:29:22</div> <div>1038 Java™ 2: The Complete Reference<br /> source index counter each time, and there will be a speed benefit from using the array<br /> copy method for a particular line.<br /> The Code<br /> Here is the source code for the TearTransition class:<br /> import java.awt.*;<br /> import java.awt.image.*;<br /> public class TearTransition extends BillTransition {<br /> static final int CELLS = 7;<br /> static final float INITIAL_X_CROSS = 1.6f;<br /> static final float X_CROSS_DIVISOR = 3.5f;<br /> float x_cross;<br /> public void init(Component owner, int[] current, int[] next) {<br /> init(owner, current, next, CELLS);<br /> System.arraycopy(next_pixels, 0, work_pixels, 0,<br /> pixels_per_cell);<br /> System.arraycopy(current_pixels, 0, work_pixels, 0, cell_w);<br /> }<br /> x_cross = INITIAL_X_CROSS;<br /> for(int c = CELLS - 1; c >= 0; --c) {<br /> try { Thread.sleep(100); } catch (InterruptedException e) {}<br /> Tear();<br /> try { Thread.sleep(150); } catch (InterruptedException e) {}<br /> createCellFromWorkPixels(c);<br /> x_cross /= X_CROSS_DIVISOR;<br /> }<br /> work_pixels = null;<br /> final void Tear() {<br /> float x_increment;<br /> int p, height_adder;<br /> p = height_adder = cell_w;<br /> for (int y = 1; y < cell_h; ++y) {<br /> x_increment = x_cross * y;<br /> if(x_increment >= 0.50f) {<br /> float fx = 0.0f;</div> <div>THE JAVA LIBRARY<br /> Chapter 24: New I/O, Regular Expressions, and Other Packages 859<br /> }<br /> }<br /> System.exit(1);<br /> }<br /> Because the input file is mapped to mBuf, it contains the entire source file. Thus, the<br /> call to write( ) copies all of mBuf to the target file. This, of course, means that the target<br /> file is an identical copy of the source file.<br /> Is NIO the Future of I/O Handling?<br /> The new I/O APIs offer an exciting new way to think about and handle some types<br /> of file operations. Because of this it is natural to ask the question, “Is NIO the future<br /> of I/O handling?” Unfortunately, at the time of this writing, this question cannot be<br /> answered. Certainly, channels and buffers offer a clean way of thinking about I/O.<br /> However, they also add another layer of abstraction. Furthermore, the traditional<br /> stream-based approach is both well-understood, and widely used. As explained at<br /> the outset, channel-based I/O is currently designed to supplement, not replace the<br /> standard I/O mechanisms defined in java.io.Inthis role, the channel/buffer approach<br /> used by the NIO APIs succeeds admirably. Whether the new approach will someday<br /> supplant the traditional approach, only time and usage patterns will tell.<br /> Regular Expression Processing<br /> Another exciting package added by Java 2, version 1.4 is java.util.regex, which<br /> supports regular expression processing. As the term is used here, a regular expression is<br /> a string of characters that describes a character sequence. This general description,<br /> called a pattern, can then be used to find matches in other character sequences. Regular<br /> expressions can specify wildcard characters, sets of characters, and various quantifiers.<br /> Thus, you can specify a regular expression that represents a general form that can<br /> match several different specific character sequences.<br /> There are two classes that support regular expression processing: Pattern and<br /> Matcher. These classes work together. Use Pattern to define a regular expression.<br /> Match the pattern against another sequence using Matcher.<br /> Pattern<br /> The Pattern class defines no constructors. Instead, a pattern is created by calling the<br /> compile( ) factory method. One of its forms is shown here:<br /> static Pattern compile(String pattern)</div> <div>424 Java™ 2: The Complete Reference<br /> As expected, these constants specify the maximum, minimum, and default<br /> thread priorities.<br /> The methods defined by Thread are shown in Table 14-16. In versions of Java<br /> prior to 2, Thread also included the methods stop( ), suspend( ), and resume( ).<br /> However, as explained in Chapter 11, these have been deprecated by Java 2 because<br /> they were inherently unstable. Also deprecated by Java 2 is countStackFrames( ),<br /> because it calls suspend( ).<br /> Method<br /> static int activeCount( )<br /> void checkAccess( )<br /> static Thread currentThread( )<br /> void destroy( )<br /> static void dumpStack( )<br /> static int enumerate(Thread threads[ ])<br /> ClassLoader getContextClassLoader( )<br /> final String getName( )<br /> final int getPriority( )<br /> final ThreadGroup getThreadGroup( )<br /> static boolean holdsLock(Object ob)<br /> Description<br /> Returns the number of threads in the<br /> group to which the thread belongs.<br /> Causes the security manager to verify<br /> that the current thread can access<br /> and/or change the thread on which<br /> checkAccess( ) is called.<br /> Returns a Thread object that<br /> encapsulates the thread that calls<br /> this method.<br /> Terminates the thread.<br /> Displays the call stack for the thread.<br /> Puts copies of all Thread objects in the<br /> current thread’s group into threads. The<br /> number of threads is returned.<br /> Returns the class loader that is used to<br /> load classes and resources for this<br /> thread. (Added by Java 2)<br /> Returns the thread’s name.<br /> Returns the thread’s priority setting.<br /> Returns the ThreadGroup object of<br /> which the invoking thread is a member.<br /> Returns true if the invoking thread<br /> owns the lock on ob. Returns false<br /> otherwise. (Added by Java 2, version 1.4)<br /> Table 14-16.<br /> The Methods Defined by Thread</div> <div>840 Java™ 2: The Complete Reference<br /> }<br /> }<br /> public void run() {<br /> idx = 0;<br /> while (true) {<br /> paint(getGraphics());<br /> idx = (idx + 1) % nseq;<br /> try { Thread.sleep(1000/framerate); } catch (Exception e) { };<br /> if(stopFlag)<br /> return;<br /> }<br /> }<br /> The following applet tag shows the famous locomotion study by Eadweard<br /> Muybridge, which proved that horses do, indeed, get all four hooves off the ground at<br /> once. (Of course, you can substitute another image file in your own applet.)<br /> <applet code=Animation width=67 height=48><br /> <param name=img value=horse.gif><br /> <param name=rows value=3><br /> <param name=cols value=4><br /> <param name=sequence value=0,1,2,3,4,5,6,7,8,9,10><br /> <param name=framerate value=15><br /> </applet><br /> Figure 23-13 shows the applet running. Notice the source image that has been loaded<br /> below the applet using a normal <img> tag.<br /> Additional Imaging Classes<br /> In addition to the imaging classes described in this chapter, java.awt.image supplies several<br /> others that offer enhanced control over the imaging process and that support advanced</div> <div>This page intentionally left blank.</div> <div>938 Java™ 2: The Complete Reference<br /> }<br /> }<br /> JCheckBox cb1 = new JCheckBox("Red");<br /> add(cb1);<br /> JCheckBox cb2 = new JCheckBox("Green");<br /> add(cb2);<br /> JCheckBox cb3 = new JCheckBox("Blue");<br /> add(cb3);<br /> class FlavorsPanel extends JPanel {<br /> public FlavorsPanel() {<br /> }<br /> }<br /> JComboBox jcb = new JComboBox();<br /> jcb.addItem("Vanilla");<br /> jcb.addItem("Chocolate");<br /> jcb.addItem("Strawberry");<br /> add(jcb);<br /> Output from this applet is shown in the following three illustrations:</div> <div>18 Java™ 2: The Complete Reference<br /> Like all other computer languages, the elements of Java do not exist in isolation.<br /> Rather, they work together to form the language as a whole. However, this<br /> interrelatedness can make it difficult to describe one aspect of Java without<br /> involving several others. Often a discussion of one feature implies prior knowledge<br /> of another. For this reason, this chapter presents a quick overview of several key<br /> features of Java. The material described here will give you a foothold that will allow<br /> you to write and understand simple programs. Most of the topics discussed will be<br /> examined in greater detail in the remaining chapters of Part 1.<br /> Object-Oriented Programming<br /> Object-oriented programming is at the core of Java. In fact, all Java programs are objectoriented—this<br /> isn’t an option the way that it is in C++, for example. OOP is so integral<br /> to Java that you must understand its basic principles before you can write even simple<br /> Java programs. Therefore, this chapter begins with a discussion of the theoretical aspects<br /> of OOP.<br /> Two Paradigms<br /> As you know, all computer programs consist of two elements: code and data. Furthermore,<br /> a program can be conceptually organized around its code or around its data. That is,<br /> some programs are written around “what is happening” and others are written around<br /> “who is being affected.” These are the two paradigms that govern how a program is<br /> constructed. The first way is called the process-oriented model. This approach characterizes<br /> a program as a series of linear steps (that is, code). The process-oriented model can be<br /> thought of as code acting on data. Procedural languages such as C employ this model to<br /> considerable success. However, as mentioned in Chapter 1, problems with this approach<br /> appear as programs grow larger and more complex.<br /> To manage increasing complexity, the second approach, called object-oriented<br /> programming, was conceived. Object-oriented programming organizes a program around<br /> its data (that is, objects) and a set of well-defined interfaces to that data. An object-oriented<br /> program can be characterized as data controlling access to code. As you will see, by switching<br /> the controlling entity to data, you can achieve several organizational benefits.<br /> Abstraction<br /> An essential element of object-oriented programming is abstraction. Humans manage<br /> complexity through abstraction. For example, people do not think of a car as a set of<br /> tens of thousands of individual parts. They think of it as a well-defined object with its<br /> own unique behavior. This abstraction allows people to use a car to drive to the grocery<br /> store without being overwhelmed by the complexity of the parts that form the car. They<br /> can ignore the details of how the engine, transmission, and braking systems work. Instead<br /> they are free to utilize the object as a whole.</div> <div>THE JAVA LIBRARY<br /> Chapter 14: Exploring java.lang 383<br /> Method<br /> static int floatToIntBits(float num)<br /> float floatValue( )<br /> int hashCode( )<br /> static float intBitsToFloat(int num)<br /> int intValue( )<br /> boolean isInfinite( )<br /> static boolean isInfinite(float num)<br /> boolean isNaN( )<br /> static boolean isNaN(float num)<br /> long longValue( )<br /> static float parseFloat(String str)<br /> throws NumberFormatException<br /> short shortValue( )<br /> String toString( )<br /> static String toString(float num)<br /> static Float valueOf(String str)<br /> throws NumberFormatException<br /> Description<br /> Returns the IEEE-compatible,<br /> single-precision bit pattern that<br /> corresponds to the num.<br /> Returns the value of the invoking object as<br /> a float.<br /> Returns the hash code for the invoking object.<br /> Returns float equivalent of the<br /> IEEE-compatible, single-precision bit<br /> pattern specified by num.<br /> Returns the value of the invoking object as<br /> an int.<br /> Returns true if the invoking object contains<br /> an infinite value. Otherwise, it returns false.<br /> Returns true if num specifies an infinite<br /> value. Otherwise, it returns false.<br /> Returns true if the invoking object<br /> contains a value that is not a number.<br /> Otherwise, it returns false.<br /> Returns true if num specifies a value that is<br /> not a number. Otherwise, it returns false.<br /> Returns the value of the invoking object as<br /> a long.<br /> Returns the float equivalent of the number<br /> contained in the string specified by str<br /> using radix 10. (Added by Java 2)<br /> Returns the value of the invoking object as<br /> a short.<br /> Returns the string equivalent of the<br /> invoking object.<br /> Returns the string equivalent of the value<br /> specified by num.<br /> Returns the Float object that contains the<br /> value specified by the string in str.<br /> Table 14-1.<br /> The Methods Defined by Float (continued)</div> <div>THE JAVA LIBRARY<br /> Chapter 16: java.util Part 2: More Utility Classes 521<br /> TimeZone<br /> Another time-related class is TimeZone. The TimeZone class allows you to work with<br /> time zone offsets from Greenwich mean time (GMT), also referred to as Coordinated<br /> Universal Time (UTC). It also computes daylight saving time. TimeZone only supplies<br /> the default constructor.<br /> Some methods defined by TimeZone are summarized in Table 16-5.<br /> Method<br /> Object clone( )<br /> static String[ ] getAvailableIDs( )<br /> static String[ ] getAvailableIDs(int timeDelta)<br /> static TimeZone getDefault( )<br /> String getID( )<br /> abstract int getOffset(int era, int year,<br /> int month,<br /> int dayOfMonth,<br /> int dayOfWeek,<br /> int millisec)<br /> abstract int getRawOffset( )<br /> Description<br /> Returns a TimeZone-specific<br /> version of clone( ).<br /> Returns an array of String<br /> objects representing the names<br /> of all time zones.<br /> Returns an array of String objects<br /> representing the names of all time<br /> zones that are timeDelta offset<br /> from GMT.<br /> Returns a TimeZone object that<br /> represents the default time zone<br /> used on the host computer.<br /> Returns the name of the invoking<br /> TimeZone object.<br /> Returns the offset that should be<br /> added to GMT to compute local<br /> time. This value is adjusted for<br /> daylight saving time. The<br /> parameters to the method<br /> represent date and time<br /> components.<br /> Returns the raw offset that should<br /> be added to GMT to compute local<br /> time. This value is not adjusted for<br /> daylight saving time.<br /> Table 16-5.<br /> Some of the Methods Defined by TimeZone</div> <div>204 Java™ 2: The Complete Reference<br /> }<br /> depth = d;<br /> }<br /> // constructor used when no dimensions specified<br /> Box() {<br /> width = -1; // use -1 to indicate<br /> height = -1; // an uninitialized<br /> depth = -1; // box<br /> }<br /> // constructor used when cube is created<br /> Box(double len) {<br /> width = height = depth = len;<br /> }<br /> // compute and return volume<br /> double volume() {<br /> return width * height * depth;<br /> }<br /> // Add weight.<br /> class BoxWeight extends Box {<br /> double weight; // weight of box<br /> // construct clone of an object<br /> BoxWeight(BoxWeight ob) { // pass object to constructor<br /> super(ob);<br /> weight = ob.weight;<br /> }<br /> // constructor when all parameters are specified<br /> BoxWeight(double w, double h, double d, double m) {<br /> super(w, h, d); // call superclass constructor<br /> weight = m;<br /> }<br /> // default constructor<br /> BoxWeight() {<br /> super();<br /> weight = -1;<br /> }</div> <div>THE JAVA LANGUAGE<br /> Chapter 11: Multithreaded Programming 303<br /> To understand deadlock fully, it is useful to see it in action. The next example creates<br /> two classes, A and B, with methods foo( ) and bar( ), respectively, which pause briefly<br /> before trying to call a method in the other class. The main class, named Deadlock, creates<br /> an A and a B instance, and then starts a second thread to set up the deadlock condition.<br /> The foo( ) and bar( ) methods use sleep( ) as a way to force the deadlock condition<br /> to occur.<br /> // An example of deadlock.<br /> class A {<br /> synchronized void foo(B b) {<br /> String name = Thread.currentThread().getName();<br /> }<br /> }<br /> System.out.println(name + " entered A.foo");<br /> try {<br /> Thread.sleep(1000);<br /> } catch(Exception e) {<br /> System.out.println("A Interrupted");<br /> }<br /> System.out.println(name + " trying to call B.last()");<br /> b.last();<br /> synchronized void last() {<br /> System.out.println("Inside A.last");<br /> }<br /> class B {<br /> synchronized void bar(A a) {<br /> String name = Thread.currentThread().getName();<br /> System.out.println(name + " entered B.bar");<br /> try {<br /> Thread.sleep(1000);<br /> } catch(Exception e) {<br /> System.out.println("B Interrupted");<br /> }<br /> System.out.println(name + " trying to call A.last()");<br /> a.last();</div> <div>584 Java™ 2: The Complete Reference<br /> MyClass object1 = new MyClass("Hello", -7, 2.7e10);<br /> System.out.println("object1: " + object1);<br /> FileOutputStream fos = new FileOutputStream("serial");<br /> ObjectOutputStream oos = new ObjectOutputStream(fos);<br /> oos.writeObject(object1);<br /> oos.flush();<br /> oos.close();<br /> }<br /> catch(Exception e) {<br /> System.out.println("Exception during serialization: " + e);<br /> System.exit(0);<br /> }<br /> }<br /> }<br /> // Object deserialization<br /> try {<br /> MyClass object2;<br /> FileInputStream fis = new FileInputStream("serial");<br /> ObjectInputStream ois = new ObjectInputStream(fis);<br /> object2 = (MyClass)ois.readObject();<br /> ois.close();<br /> System.out.println("object2: " + object2);<br /> }<br /> catch(Exception e) {<br /> System.out.println("Exception during deserialization: " + e);<br /> System.exit(0);<br /> }<br /> class MyClass implements Serializable {<br /> String s;<br /> int i;<br /> double d;<br /> public MyClass(String s, int i, double d) {<br /> this.s = s;<br /> this.i = i;<br /> this.d = d;<br /> }<br /> public String toString() {<br /> return "s=" + s + "; i=" + i + "; d=" + d;<br /> }<br /> }</div> <div>788 Java™ 2: The Complete Reference<br /> }<br /> f.setVisible(false);<br /> }<br /> Here is sample output from the DialogDemo applet:<br /> On your own, try defining dialog boxes for the other options presented by the menus.<br /> FileDialog<br /> Java provides a built-in dialog box that lets the user specify a file. To create a file dialog<br /> box, instantiate an object of type FileDialog. This causes a file dialog box to be displayed.<br /> Usually, this is the standard file dialog box provided by the operating system. FileDialog<br /> provides these constructors:<br /> FileDialog(Frame parent, String boxName)<br /> FileDialog(Frame parent, String boxName, int how)<br /> FileDialog(Frame parent)<br /> Here, parent is the owner of the dialog box, and boxName is the name displayed in<br /> the box’s title bar. If boxName is omitted, the title of the dialog box is empty. If how is<br /> FileDialog.LOAD, then the box is selecting a file for reading. If how is FileDialog.SAVE,<br /> the box is selecting a file for writing. The third constructor creates a dialog box for selecting<br /> a file for reading.</div> <div>THE JAVA LANGUAGE<br /> Chapter 10: Exception Handling 261<br /> This program gets two chances to deal with the same error. First, main( ) sets up an<br /> exception context and then calls demoproc( ). The demoproc( ) method then sets up<br /> another exception-handling context and immediately throws a new instance of<br /> NullPointerException, which is caught on the next line. The exception is then<br /> rethrown. Here is the resulting output:<br /> Caught inside demoproc.<br /> Recaught: java.lang.NullPointerException: demo<br /> The program also illustrates how to create one of Java’s standard exception objects.<br /> Pay close attention to this line:<br /> throw new NullPointerException("demo");<br /> Here, new is used to construct an instance of NullPointerException. All of Java’s<br /> built-in run-time exceptions have at least two constructors: one with no parameter<br /> and one that takes a string parameter. When the second form is used, the argument<br /> specifies a string that describes the exception. This string is displayed when the object<br /> is used as an argument to print( ) or println( ). It can also be obtained by a call to<br /> getMessage( ), which is defined by Throwable.<br /> throws<br /> If a method is capable of causing an exception that it does not handle, it must specify<br /> this behavior so that callers of the method can guard themselves against that exception.<br /> You do this by including a throws clause in the method’s declaration. A throws clause<br /> lists the types of exceptions that a method might throw. This is necessary for all<br /> exceptions, except those of type Error or RuntimeException, or any of their subclasses.<br /> All other exceptions that a method can throw must be declared in the throws clause. If<br /> they are not, a compile-time error will result.<br /> This is the general form of a method declaration that includes a throws clause:<br /> type method-name(parameter-list) throws exception-list<br /> {<br /> // body of method<br /> }<br /> Here, exception-list is a comma-separated list of the exceptions that a method can throw.</div> <div>978 Java™ 2: The Complete Reference<br /> A session can be created via the getSession( ) method of HttpServletRequest. An<br /> HttpSession object is returned. This object can store a set of bindings that associate<br /> names with objects. The setAttribute( ), getAttribute( ), getAttributeNames( ), and<br /> removeAttribute( ) methods of HttpSession manage these bindings. It is important<br /> to note that session state is shared among all the servlets that are associated with a<br /> particular client.<br /> The following servlet illustrates how to use session state. The getSession( ) method<br /> gets the current session. A new session is created if one does not already exist. The<br /> getAttribute( ) method is called to obtain the object that is bound to the name “date”.<br /> That object is a Date object that encapsulates the date and time when this page was last<br /> accessed. (Of course, there is no such binding when the page is first accessed.) A Date<br /> object encapsulating the current date and time is then created. The setAttribute( )<br /> method is called to bind the name “date” to this object.<br /> import java.io.*;<br /> import java.util.*;<br /> import javax.servlet.*;<br /> import javax.servlet.http.*;<br /> public class DateServlet extends HttpServlet {<br /> public void doGet(HttpServletRequest request,<br /> HttpServletResponse response)<br /> throws ServletException, IOException {<br /> // Get the HttpSession object.<br /> HttpSession hs = request.getSession(true);<br /> // Get writer.<br /> response.setContentType("text/html");<br /> PrintWriter pw = response.getWriter();<br /> pw.print("<B>");<br /> // Display date/time of last access.<br /> Date date = (Date)hs.getAttribute("date");<br /> if(date != null) {<br /> pw.print("Last access: " + date + "<br>");<br /> }<br /> // Display current date/time.<br /> date = new Date();<br /> hs.setAttribute("date", date);</div> <div>APPLYING JAVA<br /> Chapter 32: Scrabblet: A Multiplayer Word Game 1105<br /> offGraphics.setColor(Color.black);<br /> offGraphics.fillRect(lm,tm,aw-2*lt,ah-2*lt);<br /> lm += lt;<br /> tm += lt;<br /> offGraphics.setColor(Color.white);<br /> offGraphics.fillRect(lm,tm,aw-4*lt,ah-4*lt);<br /> lm += lt;<br /> tm += lt;<br /> int sfh = (lh > 30) ? lh / 4 : lh / 2;<br /> Font font = new Font("SansSerif", Font.PLAIN, sfh);<br /> offGraphics.setFont(font);<br /> for (int j = 0, y = tm; j < 15; j++, y += lh + lt) {<br /> for (int i = 0, x = lm; i < 15; i++, x += lw + lt) {<br /> Color c = tiles[j < 8 ? j : 14 - j][i < 8 ? i : 14 - i];<br /> offGraphics.setColor(c);<br /> offGraphics.fillRect(x, y, lw, lh);<br /> offGraphics.setColor(Color.black);<br /> if (lh > 30) {<br /> String td = (c == w2 || c == l2) ? "DOUBLE" :<br /> (c == w3 || c == l3) ? "TRIPLE" : null;<br /> String wl = (c == l2 || c == l3) ? "LETTER" :<br /> (c == w2 || c == w3) ? "WORD" : null;<br /> if (td != null) {<br /> center(offGraphics, td, x, y + 2 + sfh, lw);<br /> center(offGraphics, wl, x, y + 2 * (2 + sfh), lw);<br /> center(offGraphics, "SCORE", x, y + 3 * (2 + sfh), lw);<br /> }<br /> } else {<br /> String td = (c == w2 || c == l2) ? "2" :<br /> (c == w3 || c == l3) ? "3" : null;<br /> String wl = (c == l2 || c == l3) ? "L" :<br /> (c == w2 || c == w3) ? "W" : null;<br /> if (td != null) {<br /> center(offGraphics, td + wl, x,<br /> y + (lh - sfh) * 4 / 10 + sfh, lw);<br /> }<br /> }<br /> }<br /> }<br /> Color c = new Color(255, 255, 200);<br /> offGraphics.setColor(c);</div> <div>THE JAVA LANGUAGE<br /> Chapter 2: An Overview of Java 31<br /> assigns to num the value 100. In Java, the assignment operator is a single equal sign.<br /> The next line of code outputs the value of num preceded by the string “This is num:”.<br /> System.out.println("This is num: " + num);<br /> In this statement, the plus sign causes the value of num to be appended to the string<br /> that precedes it, and then the resulting string is output. (Actually, num is first converted<br /> from an integer into its string equivalent and then concatenated with the string that<br /> precedes it. This process is described in detail later in this book.) This approach can be<br /> generalized. Using the + operator, you can string together as many items as you want<br /> within a single println( ) statement.<br /> The next line of code assigns num the value of num times 2. Like most other<br /> languages, Java uses the * operator to indicate multiplication. After this line executes,<br /> num will contain the value 200.<br /> Here are the next two lines in the program:<br /> System.out.print("The value of num * 2 is ");<br /> System.out.println(num);<br /> Several new things are occurring here. First, the built-in method print( ) is used to<br /> display the string “The value of num * 2 is ”. This string is not followed by a newline.<br /> This means that when the next output is generated, it will start on the same line. The<br /> print( ) method is just like println( ), except that it does not output a newline character<br /> after each call. Now look at the call to println( ). Notice that num is used by itself. Both<br /> print( ) and println( ) can be used to output values of any of Java’s built-in types.<br /> Two Control Statements<br /> Although Chapter 5 will look closely at control statements, two are briefly introduced<br /> here so that they can be used in example programs in Chapters 3 and 4. They will also<br /> help illustrate an important aspect of Java: blocks of code.<br /> The if Statement<br /> The Java if statement works much like the IF statement in any other language. Further,<br /> it is syntactically identical to the if statements in C, C++, and C#. Its simplest form is<br /> shown here:<br /> if(condition) statement;</div> <div>782 Java™ 2: The Complete Reference<br /> }<br /> f.setVisible(true);<br /> }<br /> public void stop() {<br /> f.setVisible(false);<br /> }<br /> Sample output from the MenuDemo applet is shown in Figure 22-8.<br /> There is one other menu-related class that you might find interesting: PopupMenu.<br /> It works just like Menu but produces a menu that can be displayed at a specific location.<br /> PopupMenu provides a flexible, useful alternative for some types of menuing situations.<br /> Dialog Boxes<br /> Often, you will want to use a dialog box to hold a set of related controls. Dialog boxes<br /> are primarily used to obtain user input. They are similar to frame windows, except that<br /> dialog boxes are always child windows of a top-level window. Also, dialog boxes don’t<br /> have menu bars. In other respects, dialog boxes function like frame windows. (You can<br /> add controls to them, for example, in the same way that you add controls to a frame<br /> window.) Dialog boxes may be modal or modeless. When a modal dialog box is active,<br /> Figure 22-8.<br /> Sample output from the MenuDemo applet</div> <div>THE JAVA LIBRARY<br /> Chapter 23: Images 801<br /> Image Fundamentals: Creating, Loading,<br /> and Displaying<br /> There are three common operations that occur when you work with images: creating<br /> an image, loading an image, and displaying an image. In Java, the Image class is used<br /> to refer to images in memory and to images that must be loaded from external sources.<br /> Thus, Java provides ways for you to create a new image object and ways to load one. It<br /> also provides a means by which an image can be displayed. Let’s look at each.<br /> Creating an Image Object<br /> You might expect that you create a memory image using something like the following:<br /> Image test = new Image(200, 100); // Error -- won't work<br /> Not so. Because images must eventually be painted on a window to be seen, the Image<br /> class doesn’t have enough information about its environment to create the proper data<br /> format for the screen. Therefore, the Component class in java.awt has a factory method<br /> called createImage( ) that is used to create Image objects. (Remember that all of the<br /> AWT components are subclasses of Component, so all support this method.)<br /> The createImage( ) method has the following two forms:<br /> Image createImage(ImageProducer imgProd)<br /> Image createImage(int width, int height)<br /> The first form returns an image produced by imgProd, which is an object of a class that<br /> implements the ImageProducer interface. (We will look at image producers later.)<br /> The second form returns a blank (that is, empty) image that has the specified width<br /> and height. Here is an example:<br /> Canvas c = new Canvas();<br /> Image test = c.createImage(200, 100);<br /> This creates an instance of Canvas and then calls the createImage( ) method to actually<br /> make an Image object. At this point, the image is blank. Later you will see how to write<br /> data to it.<br /> Loading an Image<br /> The other way to obtain an image is to load one. To do this, use the getImage( ) method<br /> defined by the Applet class. It has the following forms:<br /> Image getImage(URL url)<br /> Image getImage(URL url, String imageName)</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 27: Servlets 979<br /> }<br /> pw.println("Current date: " + date);<br /> }<br /> When you first request this servlet, the browser displays one line with the current<br /> date and time information. On subsequent invocations, two lines are displayed. The<br /> first line shows the date and time when the servlet was last accessed. The second line<br /> shows the current date and time.<br /> Security Issues<br /> In earlier chapters of this book, you learned that untrusted applets are constrained<br /> to operate in a “sandbox”. They cannot perform operations that are potentially<br /> dangerous to a user’s machine. This includes reading and writing files, opening<br /> sockets to arbitrary machines, calling native methods, and creating new processes.<br /> Other restrictions also apply.<br /> Similar constraints also exist for untrusted servlets. Code that is loaded from a<br /> remote machine is untrusted. However, trusted servlets are not limited in this manner.<br /> Trusted servlets are those which are loaded from the local machine.</div> <div>368 Java™ 2: The Complete Reference<br /> String Methods Added by Java 2, Version 1.4<br /> Java 2, version 1.4 adds several methods to the String class. These are summarized in<br /> the following table.<br /> Method<br /> boolean contentEquals(StringBuffer str)<br /> CharSequence<br /> subSequence(int startIndex,<br /> int stopIndex)<br /> boolean matches(string regExp)<br /> String<br /> replaceFirst(String regExp,<br /> String newStr)<br /> String<br /> replaceAll(String regExp,<br /> String newStr)<br /> String[ ] split(String regExp)<br /> String[ ] split(String regExp, int max)<br /> Description<br /> Returns true if the invoking string contains<br /> the same string as str. Otherwise, returns<br /> false.<br /> Returns a substring of the invoking string,<br /> beginning at startIndex and stopping at<br /> stopIndex. This method is required by the<br /> CharSequence interface, which is now<br /> implemented by String.<br /> Returns true if the invoking string matches<br /> the regular expression passed in regExp.<br /> Otherwise, returns false.<br /> Returns a string in which the first substring<br /> that matches the regular expression<br /> specified by regExp is replaced by newStr.<br /> Returns a string in which all substrings that<br /> match the regular expression specified by<br /> regExp are replaced by newStr.<br /> Decomposes the invoking string into parts<br /> and returns an array that contains the<br /> result. Each part is delimited by the regular<br /> expression passed in regExp.<br /> Decomposes the invoking string into parts<br /> and returns an array that contains the<br /> result. Each part is delimited by the regular<br /> expression passed in regExp. The number<br /> of pieces is specified by max. If max is<br /> negative, then the invoking string is fully<br /> decomposed. Otherwise, if max contains<br /> a non-zero value, the last entry in the<br /> returned array contains the remainder<br /> of the invoking string. If max is zero, the<br /> invoking string is fully decomposed.</div> <div>THE JAVA LANGUAGE<br /> Chapter 12: I/O, Applets, and Other Topics 321<br /> public static void main(String args[])<br /> throws IOException<br /> {<br /> // create a BufferedReader using System.in<br /> BufferedReader br = new BufferedReader(new<br /> InputStreamReader(System.in));<br /> String str;<br /> }<br /> }<br /> System.out.println("Enter lines of text.");<br /> System.out.println("Enter 'stop' to quit.");<br /> do {<br /> str = br.readLine();<br /> System.out.println(str);<br /> } while(!str.equals("stop"));<br /> The next example creates a tiny text editor. It creates an array of String objects and<br /> then reads in lines of text, storing each line in the array. It will read up to 100 lines or<br /> until you enter “stop”. It uses a BufferedReader to read from the console.<br /> // A tiny editor.<br /> import java.io.*;<br /> class TinyEdit {<br /> public static void main(String args[])<br /> throws IOException<br /> {<br /> // create a BufferedReader using System.in<br /> BufferedReader br = new BufferedReader(new<br /> InputStreamReader(System.in));<br /> String str[] = new String[100];<br /> System.out.println("Enter lines of text.");<br /> System.out.println("Enter 'stop' to quit.");<br /> for(int i=0; i<100; i++) {<br /> str[i] = br.readLine();<br /> if(str[i].equals("stop")) break;<br /> }<br /> System.out.println("\nHere is your file:");</div> <div>446 Java™ 2: The Complete Reference<br /> Method<br /> void add(int index, Object obj)<br /> boolean addAll(int index, Collection c)<br /> Object get(int index)<br /> int indexOf(Object obj)<br /> int lastIndexOf(Object obj)<br /> ListIterator listIterator( )<br /> ListIterator listIterator(int index)<br /> Object remove(int index)<br /> Object set(int index, Object obj)<br /> List subList(int start, int end)<br /> Description<br /> Inserts obj into the invoking list at the<br /> index passed in index. Any preexisting<br /> elements at or beyond the point of<br /> insertion are shifted up. Thus, no<br /> elements are overwritten.<br /> Inserts all elements of c into the invoking<br /> list at the index passed in index. Any<br /> preexisting elements at or beyond the<br /> point of insertion are shifted up. Thus,<br /> no elements are overwritten. Returns<br /> true if the invoking list changes and<br /> returns false otherwise.<br /> Returns the object stored at the specified<br /> index within the invoking collection.<br /> Returns the index of the first instance of<br /> obj in the invoking list. If obj is not an<br /> element of the list, –1 is returned.<br /> Returns the index of the last instance of<br /> obj in the invoking list. If obj is not an<br /> element of the list, –1 is returned.<br /> Returns an iterator to the start of the<br /> invoking list.<br /> Returns an iterator to the invoking list<br /> that begins at the specified index.<br /> Removes the element at position index from<br /> the invoking list and returns the deleted<br /> element. The resulting list is compacted.<br /> That is, the indexes of subsequent elements<br /> are decremented by one.<br /> Assigns obj to the location specified by<br /> index within the invoking list.<br /> Returns a list that includes elements<br /> from start to end–1 in the invoking list.<br /> Elements in the returned list are also<br /> referenced by the invoking object.<br /> Table 15-2.<br /> The Methods Defined by List</div> <div>THE JAVA LIBRARY<br /> Chapter 21: Introducing the AWT: Working with Windows, Graphics, and Text 721<br /> // Show fonts.<br /> import java.applet.*;<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> /*<br /> <applet code="SampleFonts" width=200 height=100><br /> </applet><br /> */<br /> public class SampleFonts extends Applet {<br /> int next = 0;<br /> Font f;<br /> String msg;<br /> public void init() {<br /> f = new Font("Dialog", Font.PLAIN, 12);<br /> msg = "Dialog";<br /> setFont(f);<br /> addMouseListener(new MyMouseAdapter(this));<br /> }<br /> }<br /> public void paint(Graphics g) {<br /> g.drawString(msg, 4, 20);<br /> }<br /> class MyMouseAdapter extends MouseAdapter {<br /> SampleFonts sampleFonts;<br /> public MyMouseAdapter(SampleFonts sampleFonts) {<br /> this.sampleFonts = sampleFonts;<br /> }<br /> public void mousePressed(MouseEvent me) {<br /> // Switch fonts with each mouse click.<br /> sampleFonts.next++;<br /> switch(sampleFonts.next) {<br /> case 0:<br /> sampleFonts.f = new Font("Dialog", Font.PLAIN, 12);<br /> sampleFonts.msg = "Dialog";<br /> break;<br /> case 1:<br /> sampleFonts.f = new Font("DialogInput", Font.PLAIN, 12);<br /> sampleFonts.msg = "DialogInput";<br /> break;<br /> case 2:</div> <div>98 Java™ 2: The Complete Reference<br /> In addition to altering the normal precedence of an operator, parentheses can<br /> sometimes be used to help clarify the meaning of an expression. For anyone reading<br /> your code, a complicated expression can be difficult to understand. Adding redundant<br /> but clarifying parentheses to complex expressions can help prevent confusion later. For<br /> example, which of the following expressions is easier to read?<br /> a | 4 + c >> b & 7<br /> (a | (((4 + c) >> b) & 7))<br /> One other point: parentheses (redundant or not) do not degrade the performance of<br /> your program. Therefore, adding parentheses to reduce ambiguity does not negatively<br /> affect your program.</div> <div>670 Java™ 2: The Complete Reference<br /> The ActionListener Interface<br /> This interface defines the actionPerformed( ) method that is invoked when an action<br /> event occurs. Its general form is shown here:<br /> void actionPerformed(ActionEvent ae)<br /> The AdjustmentListener Interface<br /> This interface defines the adjustmentValueChanged( ) method that is invoked when<br /> an adjustment event occurs. Its general form is shown here:<br /> void adjustmentValueChanged(AdjustmentEvent ae)<br /> The ComponentListener Interface<br /> This interface defines four methods that are invoked when a component is resized,<br /> moved, shown, or hidden. Their general forms are shown here:<br /> void componentResized(ComponentEvent ce)<br /> void componentMoved(ComponentEvent ce)<br /> void componentShown(ComponentEvent ce)<br /> void componentHidden(ComponentEvent ce)<br /> The AWT processes the resize and move events. The componentResized( ) and<br /> componentMoved( ) methods are provided for notification purposes only.<br /> The ContainerListener Interface<br /> This interface contains two methods. When a component is added to a container,<br /> componentAdded( ) is invoked. When a component is removed from a container,<br /> componentRemoved( ) is invoked. Their general forms are shown here:<br /> void componentAdded(ContainerEvent ce)<br /> void componentRemoved(ContainerEvent ce)<br /> The FocusListener Interface<br /> This interface defines two methods. When a component obtains keyboard focus,<br /> focusGained( ) is invoked. When a component loses keyboard focus, focusLost( )<br /> is called. Their general forms are shown here:<br /> void focusGained(FocusEvent fe)<br /> void focusLost(FocusEvent fe)</div> <div>THE JAVA LIBRARY<br /> Chapter 13: String Handling 353<br /> Be careful when you mix other types of operations with string concatenation<br /> expressions, however. You might get surprising results. Consider the following:<br /> String s = "four: " + 2 + 2;<br /> System.out.println(s);<br /> This fragment displays<br /> four: 22<br /> rather than the<br /> four: 4<br /> that you probably expected. Here’s why. Operator precedence causes the concatenation of<br /> “four” with the string equivalent of 2 to take place first. This result is then concatenated<br /> with the string equivalent of 2 a second time. To complete the integer addition first, you<br /> must use parentheses, like this:<br /> String s = "four: " + (2 + 2);<br /> Now s contains the string “four: 4”.<br /> String Conversion and toString( )<br /> When Java converts data into its string representation during concatenation, it does so<br /> by calling one of the overloaded versions of the string conversion method valueOf( )<br /> defined by String. valueOf( ) is overloaded for all the simple types and for type Object.<br /> For the simple types, valueOf( ) returns a string that contains the human-readable<br /> equivalent of the value with which it is called. For objects, valueOf( ) calls the<br /> toString( ) method on the object. We will look more closely at valueOf( ) later in this<br /> chapter. Here, let’s examine the toString( ) method, because it is the means by which<br /> you can determine the string representation for objects of classes that you create.<br /> Every class implements toString( ) because it is defined by Object. However, the<br /> default implementation of toString( ) is seldom sufficient. For most important classes<br /> that you create, you will want to override toString( ) and provide your own string<br /> representations. Fortunately, this is easy to do. The toString( ) method has this<br /> general form:<br /> String toString( )<br /> To implement toString( ), simply return a String object that contains the humanreadable<br /> string that appropriately describes an object of your class.</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 25: Java Beans 891<br /> Create and Configure an Instance of the OurButton Bean<br /> Follow these steps to create and configure an instance of the OurButton Bean and<br /> connect it to the Molecule Bean:<br /> 1. Position the cursor on the ToolBox entry labeled OurButton and click the left<br /> mouse button. You should see the cursor change to a cross.<br /> 2. Move the cursor to the BeanBox display area and click the left mouse button in<br /> approximately the area where you wish the Bean to be displayed. You should<br /> see a rectangular region appear that contains a button. This area is surrounded<br /> by a hatched border indicating that it is currently selected.<br /> 3. You may reposition the OurButton Bean by positioning the cursor over one of<br /> the hatched borders and dragging the Bean.<br /> 4. Go to the Properties window and change the label of the Bean to “Rotate X”.<br /> The button appearance changes immediately when this property is changed.<br /> 5. Go to the menu bar of the BeanBox and select Edit | Events | action |<br /> actionPerformed. You should now see a line extending from the button to the<br /> cursor. Notice that one end of the line moves as the cursor moves. However, the<br /> other end of the line remains fixed at the button.<br /> 6. Move the cursor so that it is inside the Molecule Bean display area, and click<br /> the left mouse button. You should see the Event Target Dialog dialog box.<br /> 7. The dialog box allows you to choose a method that should be invoked when<br /> this button is clicked. Select the entry labeled “rotateOnX” and click the OK<br /> button. You should see a message box appear very briefly, stating that the tool<br /> is “Generating and compiling adaptor class.”<br /> Test the application. Each time you press the button, the molecule should move a<br /> few degrees around one of its axes.<br /> Now create another instance of the OurButton Bean. Label it “Rotate Y” and map<br /> its action event to the “rotateY” method of the Molecule Bean. The steps to do this are<br /> very similar to those just described for the button labeled “Rotate X”.<br /> Test the application by clicking these buttons and observing how the molecule moves.<br /> JAR Files<br /> Before developing your own Bean, it is necessary for you to understand JAR (Java<br /> Archive) files, because tools such as the BDK expect Beans to be packaged within JAR<br /> files. A JAR file allows you to efficiently deploy a set of classes and their associated<br /> resources. For example, a developer may build a multimedia application that uses<br /> various sound and image files. A set of Beans can control how and when this<br /> information is presented. All of these pieces can be placed into one JAR file.</div> <div>THE JAVA LANGUAGE<br /> Chapter 4: Operators 79<br /> These operators are unique in that they can appear both in postfix form, where<br /> they follow the operand as just shown, and prefix form, where they precede the<br /> operand. In the foregoing examples, there is no difference between the prefix and<br /> postfix forms. However, when the increment and/or decrement operators are part<br /> of a larger expression, then a subtle, yet powerful, difference between these two forms<br /> appears. In the prefix form, the operand is incremented or decremented before the value<br /> is obtained for use in the expression. In postfix form, the previous value is obtained for<br /> use in the expression, and then the operand is modified. For example:<br /> x = 42;<br /> y = ++x;<br /> In this case, y is set to 43 as you would expect, because the increment occurs before x is<br /> assigned to y. Thus, the line y = ++x; is the equivalent of these two statements:<br /> x = x + 1;<br /> y = x;<br /> However, when written like this,<br /> x = 42;<br /> y = x++;<br /> the value of x is obtained before the increment operator is executed, so the value of<br /> y is 42. Of course, in both cases x is set to 43. Here, the line y = x++; is the equivalent<br /> of these two statements:<br /> y = x;<br /> x = x + 1;<br /> The following program demonstrates the increment operator.<br /> // Demonstrate ++.<br /> class IncDec {<br /> public static void main(String args[]) {<br /> int a = 1;<br /> int b = 2;<br /> int c;</div> <div>THE JAVA LANGUAGE<br /> Chapter 7: A Closer Look at Methods and Classes 183<br /> // This program will not compile.<br /> class Outer {<br /> int outer_x = 100;<br /> }<br /> void test() {<br /> Inner inner = new Inner();<br /> inner.display();<br /> }<br /> // this is an inner class<br /> class Inner {<br /> int y = 10; // y is local to Inner<br /> void display() {<br /> System.out.println("display: outer_x = " + outer_x);<br /> }<br /> }<br /> void showy() {<br /> System.out.println(y); // error, y not known here!<br /> }<br /> class InnerClassDemo {<br /> public static void main(String args[]) {<br /> Outer outer = new Outer();<br /> outer.test();<br /> }<br /> }<br /> Here, y is declared as an instance variable of Inner. Thus it is not known outside of<br /> that class and it cannot be used by showy( ).<br /> Although we have been focusing on nested classes declared within an outer class<br /> scope, it is possible to define inner classes within any block scope. For example, you<br /> can define a nested class within the block defined by a method or even within the body<br /> of a for loop, as this next program shows.<br /> // Define an inner class within a for loop.<br /> class Outer {<br /> int outer_x = 100;</div> <div>THE JAVA LIBRARY<br /> Chapter 23: Images 841<br /> Figure 23-13.<br /> Sample output of Animation<br /> imaging techniques. Java 2, version 1.4 also adds a new imaging package called<br /> javax.imageio. This package supports plug-ins that handle various image formats.<br /> If sophisticated graphical output is of special interest to you, then you will want to<br /> explore the additional classes found in java.awt.image and javax.imageio.</div> <div>600 Java™ 2: The Complete Reference<br /> System.out.println("No expiration information.");<br /> else<br /> System.out.println("Expires: " + new Date(d));<br /> // get last-modified date<br /> d = hpCon.getLastModified();<br /> if(d==0)<br /> System.out.println("No last-modified information.");<br /> else<br /> System.out.println("Last-Modified: " + new Date(d));<br /> // get content length<br /> int len = hpCon.getContentLength();<br /> if(len == -1)<br /> System.out.println("Content length unavailable.");<br /> else<br /> System.out.println("Content-Length: " + len);<br /> if(len != 0) {<br /> System.out.println("=== Content ===");<br /> InputStream input = hpCon.getInputStream();<br /> int i = len;<br /> while (((c = input.read()) != -1)) { // && (--i > 0)) {<br /> System.out.print((char) c);<br /> }<br /> input.close();<br /> } else {<br /> System.out.println("No content available.");<br /> }<br /> }<br /> }<br /> The program establishes an HTTP connection to www.internic.net over port 80. We<br /> then list out the header values and retrieve the content. Here are the first lines of the<br /> output (the precise output will vary over time).<br /> Date: Sat Apr 27 12:17:32 CDT 2002<br /> Content-Type: text/html<br /> No expiration information.<br /> Last-Modified: Tue Mar 19 17:52:42 CST 2002<br /> Content-Length: 5299<br /> === Content ===</div> <div>Chapter 23<br /> Images<br /> 799</div> <div>790 Java™ 2: The Complete Reference<br /> }<br /> }<br /> FileDialog fd = new FileDialog(f, "File Dialog");<br /> fd.setVisible(true);<br /> The output generated by this program is shown here. (The precise configuration of the<br /> dialog box may vary.)<br /> Handling Events by Extending AWT<br /> Components<br /> Before concluding our look at the AWT, one more topic needs to be discussed: handling<br /> events by extending AWT components. The delegation event model was introduced in<br /> Chapter 20, and all of the programs in this book so far have used that design. But Java also<br /> allows you to handle events by subclassing AWT components. Doing so allows you to<br /> handle events in much the same way as they were handled under the original 1.0 version<br /> of Java. Of course, this technique is discouraged, because it has the same disadvantages of<br /> the Java 1.0 event model, the main one being inefficiency. Handling events by extending<br /> AWT components is described in this section for completeness. However, this technique<br /> is not used in any other sections of this book.<br /> To extend an AWT component, you must call the enableEvents( ) method of<br /> Component. Its general form is shown here:<br /> protected final void enableEvents(long eventMask)</div> <div>214 Java™ 2: The Complete Reference<br /> Dynamic, run-time polymorphism is one of the most powerful mechanisms that<br /> object-oriented design brings to bear on code reuse and robustness. The ability of<br /> existing code libraries to call methods on instances of new classes without recompiling<br /> while maintaining a clean abstract interface is a profoundly powerful tool.<br /> Applying Method Overriding<br /> Let’s look at a more practical example that uses method overriding. The following<br /> program creates a superclass called Figure that stores the dimensions of various<br /> two-dimensional objects. It also defines a method called area( ) that computes the area<br /> of an object. The program derives two subclasses from Figure. The first is Rectangle<br /> and the second is Triangle. Each of these subclasses overrides area( ) so that it returns<br /> the area of a rectangle and a triangle, respectively.<br /> // Using run-time polymorphism.<br /> class Figure {<br /> double dim1;<br /> double dim2;<br /> }<br /> Figure(double a, double b) {<br /> dim1 = a;<br /> dim2 = b;<br /> }<br /> double area() {<br /> System.out.println("Area for Figure is undefined.");<br /> return 0;<br /> }<br /> class Rectangle extends Figure {<br /> Rectangle(double a, double b) {<br /> super(a, b);<br /> }<br /> }<br /> // override area for rectangle<br /> double area() {<br /> System.out.println("Inside Area for Rectangle.");<br /> return dim1 * dim2;<br /> }<br /> class Triangle extends Figure {</div> <div>562 Java™ 2: The Complete Reference<br /> RandomAccessFile implements the standard input and output methods, which<br /> you can use to read and write to random access files. It also includes some additional<br /> methods. One is setLength( ). It has this signature:<br /> void setLength(long len) throws IOException<br /> This method sets the length of the invoking file to that specified by len. This method can be<br /> used to lengthen or shorten a file. If the file is lengthened, the added portion is undefined.<br /> Java 2, version 1.4 added the getChannel( ) method to RandomAccessFile. This<br /> method returns a channel connected to the RandomAccessFile object. Channels are<br /> used by the new I/O classes contained in java.nio. (See Chapter 24.)<br /> The Character Streams<br /> While the byte stream classes provide sufficient functionality to handle any type of I/O<br /> operation, they cannot work directly with Unicode characters. Since one of the main<br /> purposes of Java is to support the “write once, run anywhere” philosophy, it was<br /> necessary to include direct I/O support for characters. In this section, several of the<br /> character I/O classes are discussed. As explained earlier, at the top of the character<br /> stream hierarchies are the Reader and Writer abstract classes. We will begin with them.<br /> As discussed in Chapter 12, the character I/O classes were added by the 1.1 release of<br /> Java. Because of this, you may still find legacy code that uses byte streams where<br /> character streams should be. When working on such code, it is a good idea to update it.<br /> Reader<br /> Reader is an abstract class that defines Java’s model of streaming character input. All of<br /> the methods in this class will throw an IOException on error conditions. Table 17-3<br /> provides a synopsis of the methods in Reader.<br /> Writer<br /> Writer is an abstract class that defines streaming character output. All of the methods<br /> in this class return a void value and throw an IOException in the case of errors.<br /> Table 17-4 shows a synopsis of the methods in Writer.<br /> FileReader<br /> The FileReader class creates a Reader that you can use to read the contents of a file. Its<br /> two most commonly used constructors are shown here:<br /> FileReader(String filePath)<br /> FileReader(File fileObj)</div> <div>THE JAVA LANGUAGE<br /> Chapter 4: Operators 77<br /> a += 4;<br /> This version uses the += assignment operator. Both statements perform the same<br /> action: they increase the value of a by 4.<br /> Here is another example,<br /> a = a % 2;<br /> which can be expressed as<br /> a %= 2;<br /> In this case, the %= obtains the remainder of a/2 and puts that result back into a.<br /> There are assignment operators for all of the arithmetic, binary operators. Thus,<br /> any statement of the form<br /> var = var op expression;<br /> can be rewritten as<br /> var op= expression;<br /> The assignment operators provide two benefits. First, they save you a bit of typing,<br /> because they are “shorthand” for their equivalent long forms. Second, they are<br /> implemented more efficiently by the Java run-time system than are their equivalent<br /> long forms. For these reasons, you will often see the assignment operators used in<br /> professionally written Java programs.<br /> Here is a sample program that shows several op= operator assignments in action:<br /> // Demonstrate several assignment operators.<br /> class OpEquals {<br /> public static void main(String args[]) {<br /> int a = 1;<br /> int b = 2;<br /> int c = 3;<br /> a += 5;<br /> b *= 4;</div> <div>Part I<br /> The Java Language</div> <div>1000 Java™ 2: The Complete Reference<br /> }<br /> cout << "Area of 3.0 by 3.0 square: ";<br /> cout << area(3.0) << endl;<br /> return 0;<br /> As you can see, when area( ) is called with only one argument, the second defaults to<br /> zero. When this happens, the function simply uses the first argument for both the<br /> length and the width of the rectangle.<br /> While convenient, default arguments are not, of course, necessary. In essence,<br /> default arguments are actually a shorthand form of function overloading in which one<br /> form of the function has a different number of parameters than the other. Thus, to<br /> convert a C++ function that contains one or more default arguments into Java, simply<br /> create overloaded methods that handle each case. In this example, you need a version<br /> of area( ) that takes two arguments and another that takes only one argument. Using<br /> this approach, here is the preceding program rewritten for Java:<br /> // Java version of area program.<br /> class Area {<br /> // Compute area of a rectangle.<br /> static double area(double l, double w) {<br /> if(w==0) return l * l;<br /> else return l * w;<br /> }<br /> // Overload area( ) for a square.<br /> static double area(double l) {<br /> return l * l;<br /> }<br /> public static void main(String args[]) {<br /> System.out.println("Area of 2.2 by 3.4 rectangle: " +<br /> area(2.2, 3.4));<br /> }<br /> }<br /> System.out.println("Area of 3.0 by 3.0 square: " +<br /> area(3.0));</div> <div>712 Java™ 2: The Complete Reference<br /> public class ResizeMe extends Applet {<br /> final int inc = 25;<br /> int max = 500;<br /> int min = 200;<br /> Dimension d;<br /> public ResizeMe() {<br /> addMouseListener(new MouseAdapter() {<br /> public void mouseReleased(MouseEvent me) {<br /> int w = (d.width + inc) > max?min :(d.width + inc);<br /> int h = (d.height + inc) > max?min :(d.height + inc);<br /> setSize(new Dimension(w, h));<br /> }<br /> });<br /> }<br /> public void paint(Graphics g) {<br /> d = getSize();<br /> }<br /> }<br /> g.drawLine(0, 0, d.width-1, d.height-1);<br /> g.drawLine(0, d.height-1, d.width-1, 0);<br /> g.drawRect(0, 0, d.width-1, d.height-1);<br /> Working with Color<br /> Java supports color in a portable, device-independent fashion. The AWT color system<br /> allows you to specify any color you want. It then finds the best match for that color,<br /> given the limits of the display hardware currently executing your program or applet.<br /> Thus, your code does not need to be concerned with the differences in the way color is<br /> supported by various hardware devices. Color is encapsulated by the Color class.<br /> As you saw in Chapter 19, Color defines several constants (for example, Color.black)<br /> to specify a number of common colors. You can also create your own colors, using one of<br /> the color constructors. The most commonly used forms are shown here:<br /> Color(int red, int green, int blue)<br /> Color(int rgbValue)<br /> Color(float red, float green, float blue)<br /> The first constructor takes three integers that specify the color as a mix of red, green,<br /> and blue. These values must be between 0 and 255, as in this example:<br /> new Color(255, 100, 100); // light red.</div> <div>942 Java™ 2: The Complete Reference<br /> Here, tel is the listener object.<br /> The getPathForLocation( ) method is used to translate a mouse click on a specific<br /> point of the tree to a tree path. Its signature is shown here:<br /> TreePath getPathForLocation(int x, int y)<br /> Here, x and y are the coordinates at which the mouse is clicked. The return value is a<br /> TreePath object that encapsulates information about the tree node that was selected by<br /> the user.<br /> The TreePath class encapsulates information about a path to a particular node in a<br /> tree. It provides several constructors and methods. In this book, only the toString( )<br /> method is used. It returns a string equivalent of the tree path.<br /> The TreeNode interface declares methods that obtain information about a tree<br /> node. For example, it is possible to obtain a reference to the parent node or an<br /> enumeration of the child nodes. The MutableTreeNode interface extends TreeNode. It<br /> declares methods that can insert and remove child nodes or change the parent node.<br /> The DefaultMutableTreeNode class implements the MutableTreeNode interface.<br /> It represents a node in a tree. One of its constructors is shown here:<br /> DefaultMutableTreeNode(Object obj)<br /> Here, obj is the object to be enclosed in this tree node. The new tree node doesn’t have a<br /> parent or children.<br /> To create a hierarchy of tree nodes, the add( ) method of DefaultMutableTreeNode<br /> can be used. Its signature is shown here:<br /> void add(MutableTreeNode child)<br /> Here, child is a mutable tree node that is to be added as a child to the current node.<br /> Tree expansion events are described by the class TreeExpansionEvent in the<br /> javax.swing.event package. The getPath( ) method of this class returns a TreePath<br /> object that describes the path to the changed node. Its signature is shown here:<br /> TreePath getPath( )<br /> The TreeExpansionListener interface provides the following two methods:<br /> void treeCollapsed(TreeExpansionEvent tee)<br /> void treeExpanded(TreeExpansionEvent tee)<br /> Here, tee is the tree expansion event. The first method is called when a subtree is<br /> hidden, and the second method is called when a subtree becomes visible.<br /> Here are the steps that you should follow to use a tree in an applet:</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 28: Migrating from C++ to Java 993<br /> // Swap program incorrectly converted to Java.<br /> class Coord {<br /> int x;<br /> int y;<br /> };<br /> class SwapDemo {<br /> static void swap(Coord a, Coord b) {<br /> Coord temp = new Coord();<br /> }<br /> // this won't swap contents of a and b!<br /> temp = a;<br /> a = b;<br /> b = temp;<br /> public static void main(String args[]) {<br /> Coord ob1 = new Coord();<br /> Coord ob2 = new Coord();<br /> }<br /> }<br /> ob1.x = 10;<br /> ob1.y = 20;<br /> ob2.x = 88;<br /> ob2.y = 99;<br /> System.out.println("Original values:");<br /> System.out.println("ob1: " +<br /> ob1.x + ", " + ob1.y);<br /> System.out.println("ob2: " +<br /> ob2.x + ", " + ob2.y + "\n");<br /> swap(ob1, ob2);<br /> System.out.println("Swapped values:");<br /> System.out.println("ob1: " +<br /> ob1.x + ", " + ob1.y);<br /> System.out.println("ob2: " +<br /> ob2.x + ", " + ob2.y + "\n");</div> <div>THE JAVA LIBRARY<br /> Chapter 15: java.util Part 1: The Collections Framework 441<br /> The ResourceBundle, ListResourceBundle, and PropertyResourceBundle classes<br /> aid in the internationalization of large programs with many locale-specific resources.<br /> These classes are not examined here. PropertyPermission, which allows you to grant<br /> a read/write permission to a system property, is also beyond the scope of this book.<br /> EventObject, EventListener, and EventListenerProxy are described in Chapter 20. The<br /> remaining classes and interfaces are examined in detail.<br /> Because java.util is quite large, its description is broken into two chapters. This<br /> chapter examines those members of java.util that relate to collections of objects.<br /> Chapter 16 discusses the other classes and interfaces.<br /> Collections Overview<br /> The Java collections framework standardizes the way in which groups of objects are<br /> handled by your programs. Prior to Java 2, Java provided ad hoc classes such as<br /> Dictionary, Vector, Stack, and Properties to store and manipulate groups of objects.<br /> Although these classes were quite useful, they lacked a central, unifying theme. Thus,<br /> the way that you used Vector was different from the way that you used Properties, for<br /> example. Also, the previous, ad hoc approach was not designed to be easily extensible<br /> or adaptable. Collections are an answer to these (and other) problems.<br /> The collections framework was designed to meet several goals. First, the framework<br /> had to be high-performance. The implementations for the fundamental collections<br /> (dynamic arrays, linked lists, trees, and hash tables) are highly efficient. You seldom, if<br /> ever, need to code one of these “data engines” manually. Second, the framework had to<br /> allow different types of collections to work in a similar manner and with a high degree of<br /> interoperability. Third, extending and/or adapting a collection had to be easy. Toward this<br /> end, the entire collections framework is designed around a set of standard interfaces.<br /> Several standard implementations (such as LinkedList, HashSet, and TreeSet)ofthese<br /> interfaces are provided that you may use as-is. You may also implement your own<br /> collection, if you choose. Various special-purpose implementations are created for your<br /> convenience, and some partial implementations are provided that make creating your own<br /> collection class easier. Finally, mechanisms were added that allow the integration of<br /> standard arrays into the collections framework.<br /> Algorithms are another important part of the collection mechanism. Algorithms<br /> operate on collections and are defined as static methods within the Collections class.<br /> Thus, they are available for all collections. Each collection class need not implement its<br /> own versions. The algorithms provide a standard means of manipulating collections.<br /> Another item created by the collections framework is the Iterator interface. An<br /> iterator gives you a general-purpose, standardized way of accessing the elements<br /> within a collection, one at a time. Thus, an iterator provides a means of enumerating the<br /> contents of a collection. Because each collection implements Iterator, the elements of any<br /> collection class can be accessed through the methods defined by Iterator. Thus, with<br /> only small changes, the code that cycles through a set can also be used to cycle through<br /> a list, for example.</div> <div>THE JAVA LIBRARY<br /> Chapter 17: Input/Output: Exploring java.io 565<br /> while((s = br.readLine()) != null) {<br /> System.out.println(s);<br /> }<br /> }<br /> }<br /> fr.close();<br /> FileWriter<br /> FileWriter creates a Writer that you can use to write to a file. Its most commonly used<br /> constructors are shown here:<br /> FileWriter(String filePath)<br /> FileWriter(String filePath, boolean append)<br /> FileWriter(File fileObj)<br /> FileWriter(File fileObj, boolean append)<br /> They can throw an IOException. Here, filePath is the full path name of a file, and fileObj<br /> is a File object that describes the file. If append is true, then output is appended to the<br /> end of the file. The fourth constructor was added by Java 2, version 1.4.<br /> Creation of a FileWriter is not dependent on the file already existing. FileWriter<br /> will create the file before opening it for output when you create the object. In the case<br /> where you attempt to open a read-only file, an IOException will be thrown.<br /> The following example is a character stream version of an example shown earlier<br /> when FileOutputStream was discussed. This version creates a sample buffer of<br /> characters by first making a String and then using the getChars( ) method to extract<br /> the character array equivalent. It then creates three files. The first, file1.txt, will contain<br /> every other character from the sample. The second, file2.txt, will contain the entire set<br /> of characters. Finally, the third, file3.txt, will contain only the last quarter.<br /> // Demonstrate FileWriter.<br /> import java.io.*;<br /> class FileWriterDemo {<br /> public static void main(String args[]) throws Exception {<br /> String source = "Now is the time for all good men\n"<br /> + " to come to the aid of their country\n"<br /> + " and pay their due taxes.";<br /> char buffer[] = new char[source.length()];<br /> source.getChars(0, source.length(), buffer, 0);</div> <div>THE JAVA LIBRARY<br /> Chapter 20: Event Handling 675<br /> public void mousePressed(MouseEvent me) {<br /> // save coordinates<br /> mouseX = me.getX();<br /> mouseY = me.getY();<br /> msg = "Down";<br /> repaint();<br /> }<br /> // Handle button released.<br /> public void mouseReleased(MouseEvent me) {<br /> // save coordinates<br /> mouseX = me.getX();<br /> mouseY = me.getY();<br /> msg = "Up";<br /> repaint();<br /> }<br /> }<br /> // Handle mouse dragged.<br /> public void mouseDragged(MouseEvent me) {<br /> // save coordinates<br /> mouseX = me.getX();<br /> mouseY = me.getY();<br /> msg = "*";<br /> showStatus("Dragging mouse at " + mouseX + ", " + mouseY);<br /> repaint();<br /> }<br /> // Handle mouse moved.<br /> public void mouseMoved(MouseEvent me) {<br /> // show status<br /> showStatus("Moving mouse at " + me.getX() + ", " + me.getY());<br /> }<br /> // Display msg in applet window at current X,Y location.<br /> public void paint(Graphics g) {<br /> g.drawString(msg, mouseX, mouseY);<br /> }</div> <div>THE JAVA LIBRARY<br /> Chapter 15: java.util Part 1: The Collections Framework 453<br /> The first constructor builds an empty linked list. The second constructor builds a linked<br /> list that is initialized with the elements of the collection c.<br /> In addition to the methods that it inherits, the LinkedList class defines some useful<br /> methods of its own for manipulating and accessing lists. To add elements to the start of<br /> the list, use addFirst( ); to add elements to the end, use addLast( ). Their signatures are<br /> shown here:<br /> void addFirst(Object obj)<br /> void addLast(Object obj)<br /> Here, obj is the item being added.<br /> To obtain the first element, call getFirst( ). To retrieve the last element, call<br /> getLast( ). Their signatures are shown here:<br /> Object getFirst( )<br /> Object getLast( )<br /> To remove the first element, use removeFirst( ); to remove the last element, call<br /> removeLast( ). They are shown here:<br /> Object removeFirst( )<br /> Object removeLast( )<br /> The following program illustrates several of the methods supported by LinkedList:<br /> // Demonstrate LinkedList.<br /> import java.util.*;<br /> class LinkedListDemo {<br /> public static void main(String args[]) {<br /> // create a linked list<br /> LinkedList ll = new LinkedList();<br /> // add elements to the linked list<br /> ll.add("F");<br /> ll.add("B");<br /> ll.add("D");<br /> ll.add("E");<br /> ll.add("C");<br /> ll.addLast("Z");<br /> ll.addFirst("A");<br /> ll.add(1, "A2");</div> <div>26 Java™ 2: The Complete Reference<br /> guess, your operating system must be capable of supporting long filenames. This means<br /> that DOS and Windows 3.1 are not capable of supporting Java. However, Windows<br /> 95/98 and Windows NT/2000/XP work just fine.<br /> As you can see by looking at the program, the name of the class defined by the<br /> program is also Example. This is not a coincidence. In Java, all code must reside inside<br /> a class. By convention, the name of that class should match the name of the file that<br /> holds the program. You should also make sure that the capitalization of the filename<br /> matches the class name. The reason for this is that Java is case-sensitive. At this point,<br /> the convention that filenames correspond to class names may seem arbitrary. However,<br /> this convention makes it easier to maintain and organize your programs.<br /> Compiling the Program<br /> To compile the Example program, execute the compiler, javac, specifying the name of<br /> the source file on the command line, as shown here:<br /> C:\>javac Example.java<br /> The javac compiler creates a file called Example.class that contains the bytecode version<br /> of the program. As discussed earlier, the Java bytecode is the intermediate representation<br /> of your program that contains instructions the Java interpreter will execute. Thus, the<br /> output of javac is not code that can be directly executed.<br /> To actually run the program, you must use the Java interpreter, called java. To do<br /> so, pass the class name Example as a command-line argument, as shown here:<br /> C:\>java Example<br /> When the program is run, the following output is displayed:<br /> This is a simple Java program.<br /> When Java source code is compiled, each individual class is put into its own output<br /> file named after the class and using the .class extension. This is why it is a good idea to<br /> give your Java source files the same name as the class they contain—the name of the<br /> source file will match the name of the .class file. When you execute the Java interpreter<br /> as just shown, you are actually specifying the name of the class that you want the<br /> interpreter to execute. It will automatically search for a file by that name that has<br /> the .class extension. If it finds the file, it will execute the code contained in the<br /> specified class.</div> <div>344 Java™ 2: The Complete Reference<br /> To enable or disable all subpackages of a package, follow the package name with three<br /> dots. For example,<br /> -ea:MyPack...<br /> You can also specify a class with the -ea or -da option. For example, this enables<br /> AssertDemo individually.<br /> -ea:AssertDemo</div> <div>492 Java™ 2: The Complete Reference<br /> Stack st = new Stack();<br /> }<br /> }<br /> System.out.println("stack: " + st);<br /> showpush(st, 42);<br /> showpush(st, 66);<br /> showpush(st, 99);<br /> showpop(st);<br /> showpop(st);<br /> showpop(st);<br /> try {<br /> showpop(st);<br /> } catch (EmptyStackException e) {<br /> System.out.println("empty stack");<br /> }<br /> The following is the output produced by the program; notice how the exception<br /> handler for EmptyStackException is caught so that you can gracefully handle a<br /> stack underflow:<br /> stack: [ ]<br /> push(42)<br /> stack: [42]<br /> push(66)<br /> stack: [42, 66]<br /> push(99)<br /> stack: [42, 66, 99]<br /> pop -> 99<br /> stack: [42, 66]<br /> pop -> 66<br /> stack: [42]<br /> pop -> 42<br /> stack: [ ]<br /> pop -> empty stack<br /> Dictionary<br /> Dictionary is an abstract class that represents a key/value storage repository and<br /> operates much like Map. Given a key and value, you can store the value in a Dictionary</div> <div>1106 Java™ 2: The Complete Reference<br /> }<br /> offGraphics.fillRect(lm, tm + ah - 3 * lt, 7 * (lw + lt), lh +<br /> 2 * lt);<br /> Letter.resize(lw, lh);<br /> // if we already have some letters, place them.<br /> for (int i = 0; i < 7; i++) {<br /> if (tray[i] != null) {<br /> moveToTray(tray[i], i);<br /> }<br /> }<br /> paintScore();<br /> }<br /> return d;<br /> center( )<br /> center( ) is a convenience routine that checksize( ) uses to center the “Double Letter<br /> Score” text.<br /> private void center(Graphics g, String s, int x, int y, int w) {<br /> x += (w - g.getFontMetrics().stringWidth(s)) / 2;<br /> g.drawString(s, x, y);<br /> }<br /> paintScore( )<br /> The paintScore( ) method paints the two players’ scores or just the one score in<br /> single-player mode.<br /> private void paintScore() {<br /> int x = lm + (lw + lt) * 7 + lm;<br /> int y = tm + ah - 3 * lt;<br /> int h = lh + 2 * lt;<br /> Font font = new Font("TimesRoman", Font.PLAIN, h/2);<br /> offGraphics.setFont(font);<br /> FontMetrics fm = offGraphics.getFontMetrics();<br /> offGraphics.setColor(Color.white);<br /> offGraphics.fillRect(x, y, aw, h);<br /> offGraphics.setColor(Color.black);</div> <div>120 Java™ 2: The Complete Reference<br /> In addition to the jump statements discussed here, Java supports one other way that you<br /> can change your program’s flow of execution: through exception handling. Exception<br /> handling provides a structured method by which run-time errors can be trapped and<br /> handled by your program. It is supported by the keywords try, catch, throw, throws,<br /> and finally. In essence, the exception handling mechanism allows your program to<br /> perform a nonlocal branch. Since exception handling is a large topic, it is discussed<br /> in its own chapter, Chapter 10.<br /> Using break<br /> In Java, the break statement has three uses. First, as you have seen, it terminates a<br /> statement sequence in a switch statement. Second, it can be used to exit a loop. Third,<br /> it can be used as a “civilized” form of goto. The last two uses are explained here.<br /> Using break to Exit a Loop<br /> By using break, you can force immediate termination of a loop, bypassing the<br /> conditional expression and any remaining code in the body of the loop. When a break<br /> statement is encountered inside a loop, the loop is terminated and program control<br /> resumes at the next statement following the loop. Here is a simple example:<br /> // Using break to exit a loop.<br /> class BreakLoop {<br /> public static void main(String args[]) {<br /> for(int i=0; i<100; i++) {<br /> if(i == 10) break; // terminate loop if i is 10<br /> System.out.println("i: " + i);<br /> }<br /> System.out.println("Loop complete.");<br /> }<br /> }<br /> This program generates the following output:<br /> i: 0<br /> i: 1<br /> i: 2<br /> i: 3<br /> i: 4<br /> i: 5<br /> i: 6<br /> i: 7<br /> i: 8</div> <div>THE JAVA LANGUAGE<br /> Chapter 9: Packages and Interfaces 225<br /> Defining a Package<br /> To create a package is quite easy: simply include a package command as the first<br /> statement in a Java source file. Any classes declared within that file will belong to the<br /> specified package. The package statement defines a name space in which classes are<br /> stored. If you omit the package statement, the class names are put into the default<br /> package, which has no name. (This is why you haven’t had to worry about packages<br /> before now.) While the default package is fine for short, sample programs, it is<br /> inadequate for real applications. Most of the time, you will define a package for<br /> your code.<br /> This is the general form of the package statement:<br /> package pkg;<br /> Here, pkg is the name of the package. For example, the following statement creates a<br /> package called MyPackage.<br /> package MyPackage;<br /> Java uses file system directories to store packages. For example, the .class files for<br /> any classes you declare to be part of MyPackage must be stored in a directory called<br /> MyPackage. Remember that case is significant, and the directory name must match the<br /> package name exactly.<br /> More than one file can include the same package statement. The package statement<br /> simply specifies to which package the classes defined in a file belong. It does not exclude<br /> other classes in other files from being part of that same package. Most real-world packages<br /> are spread across many files.<br /> You can create a hierarchy of packages. To do so, simply separate each package<br /> name from the one above it by use of a period. The general form of a multileveled<br /> package statement is shown here:<br /> package pkg1[.pkg2[.pkg3]];<br /> A package hierarchy must be reflected in the file system of your Java development<br /> system. For example, a package declared as<br /> package java.awt.image;<br /> needs to be stored in java/awt/image, java\awt\image, or java:awt:image on your<br /> UNIX, Windows, or Macintosh file system, respectively. Be sure to choose your<br /> package names carefully. You cannot rename a package without renaming the<br /> directory in which the classes are stored.</div> <div>This page intentionally left blank.</div> <div>THE JAVA LANGUAGE<br /> Chapter 10: Exception Handling 271<br /> } catch(NullPointerException e) {<br /> // display top level exception<br /> System.out.println("Caught: " + e);<br /> }<br /> }<br /> }<br /> // display cause exception<br /> System.out.println("Original cause: " +<br /> e.getCause());<br /> The output from the program is shown here.<br /> Caught: java.lang.NullPointerException: top layer<br /> Original cause: java.lang.ArithmeticException: cause<br /> In this example, the top-level exception is NullPointerException. To it is added<br /> a cause exception, ArithmeticException. When the exception is thrown out of<br /> demoproc( ), itiscaught by main( ). There, the top-level exception is displayed,<br /> followed by the underlying exception, which is obtained by calling getCause( ).<br /> Chained exceptions can be carried on to whatever depth is necessary. Thus, the<br /> cause exception can, itself, have a cause. Be aware that overly long chains of exceptions<br /> may indicate poor design.<br /> Chained exceptions are not something that every program will need. However, in<br /> cases in which knowledge of an underlying cause is useful, they offer an elegant solution.<br /> Using Exceptions<br /> Exception handling provides a powerful mechanism for controlling complex programs<br /> that have many dynamic run-time characteristics. It is important to think of try, throw,<br /> and catch as clean ways to handle errors and unusual boundary conditions in your<br /> program’s logic. If you are like most programmers, then you probably are used to<br /> returning an error code when a method fails. When you are programming in Java, you<br /> should break this habit. When a method can fail, have it throw an exception. This is a<br /> cleaner way to handle failure modes.<br /> One last point: Java’s exception-handling statements should not be considered a<br /> general mechanism for nonlocal branching. If you do so, it will only confuse your code<br /> and make it hard to maintain.</div> <div>Chapter 17<br /> Input/Output:<br /> Exploring java.io<br /> 537</div> <div>THE JAVA LIBRARY<br /> Chapter 17: Input/Output: Exploring java.io 547<br /> Method<br /> void reset( )<br /> long skip(long numBytes)<br /> Description<br /> Resets the input pointer to the previously<br /> set mark.<br /> Ignores (that is, skips) numBytes bytes of input,<br /> returning the number of bytes actually ignored.<br /> Table 17-1.<br /> The Methods Defined by InputStream (continued)<br /> OutputStream<br /> OutputStream is an abstract class that defines streaming byte output. All of the<br /> methods in this class return a void value and throw an IOException in the case of<br /> errors. Table 17-2 shows the methods in OutputStream.<br /> Method<br /> void close( )<br /> void flush( )<br /> void write(int b)<br /> void write(byte buffer[ ])<br /> void write(byte buffer[ ], int offset,<br /> int numBytes)<br /> Description<br /> Closes the output stream. Further write<br /> attempts will generate an IOException.<br /> Finalizes the output state so that any<br /> buffers are cleared. That is, it flushes the<br /> output buffers.<br /> Writes a single byte to an output stream.<br /> Note that the parameter is an int, which<br /> allows you to call write( ) with expressions<br /> without having to cast them back to byte.<br /> Writes a complete array of bytes to an<br /> output stream.<br /> Writes a subrange of numBytes bytes from<br /> the array buffer, beginning at buffer[offset].<br /> Table 17-2.<br /> The Methods Defined by OutputStream</div> <div>28 Java™ 2: The Complete Reference<br /> comments for longer remarks and single-line comments for brief, line-by-line<br /> descriptions.<br /> The next line of code is shown here:<br /> public static void main(String args[]) {<br /> This line begins the main( ) method. As the comment preceding it suggests, this is the<br /> line at which the program will begin executing. All Java applications begin execution<br /> by calling main( ). (This is just like C/C++.) The exact meaning of each part of this line<br /> cannot be given now, since it involves a detailed understanding of Java’s approach to<br /> encapsulation. However, since most of the examples in the first part of this book will<br /> use this line of code, let’s take a brief look at each part now.<br /> The public keyword is an access specifier, which allows the programmer to control<br /> the visibility of class members. When a class member is preceded by public, then that<br /> member may be accessed by code outside the class in which it is declared. (The opposite<br /> of public is private, which prevents a member from being used by code defined outside<br /> of its class.) In this case, main( ) must be declared as public, since it must be called<br /> by code outside of its class when the program is started. The keyword static allows<br /> main( ) to be called without having to instantiate a particular instance of the class. This<br /> is necessary since main( ) is called by the Java interpreter before any objects are made.<br /> The keyword void simply tells the compiler that main( ) does not return a value. As<br /> you will see, methods may also return values. If all this seems a bit confusing, don’t<br /> worry. All of these concepts will be discussed in detail in subsequent chapters.<br /> As stated, main( ) is the method called when a Java application begins. Keep in<br /> mind that Java is case-sensitive. Thus, Main is different from main. It is important<br /> to understand that the Java compiler will compile classes that do not contain a main( )<br /> method. But the Java interpreter has no way to run these classes. So, if you had typed<br /> Main instead of main, the compiler would still compile your program. However,<br /> the Java interpreter would report an error because it would be unable to find the<br /> main( ) method.<br /> Any information that you need to pass to a method is received by variables specified<br /> within the set of parentheses that follow the name of the method. These variables are<br /> called parameters. If there are no parameters required for a given method, you still need<br /> to include the empty parentheses. In main( ), there is only one parameter, albeit a<br /> complicated one. String args[ ] declares a parameter named args, which is an array of<br /> instances of the class String. (Arrays are collections of similar objects.) Objects of type<br /> String store character strings. In this case, args receives any command-line arguments<br /> present when the program is executed. This program does not make use of this<br /> information, but other programs shown later in this book will.<br /> The last character on the line is the {. This signals the start of main( )’s body. All of<br /> the code that comprises a method will occur between the method’s opening curly brace<br /> and its closing curly brace.</div> <div>62 Java™ 2: The Complete Reference<br /> you must allocate one using new and assign it to month_days. new is a special operator<br /> that allocates memory.<br /> You will look more closely at new in a later chapter, but you need to use it now to<br /> allocate memory for arrays. The general form of new as it applies to one-dimensional<br /> arrays appears as follows:<br /> array-var = new type[size];<br /> Here, type specifies the type of data being allocated, size specifies the number of elements<br /> in the array, and array-var is the array variable that is linked to the array. That is, to use<br /> new to allocate an array, you must specify the type and number of elements to allocate.<br /> The elements in the array allocated by new will automatically be initialized to zero.<br /> This example allocates a 12-element array of integers and links them to month_days.<br /> month_days = new int[12];<br /> After this statement executes, month_days will refer to an array of 12 integers. Further,<br /> all elements in the array will be initialized to zero.<br /> Let’s review: Obtaining an array is a two-step process. First, you must declare a<br /> variable of the desired array type. Second, you must allocate the memory that will hold<br /> the array, using new, and assign it to the array variable. Thus, in Java all arrays are<br /> dynamically allocated. If the concept of dynamic allocation is unfamiliar to you, don’t<br /> worry. It will be described at length later in this book.<br /> Once you have allocated an array, you can access a specific element in the array by<br /> specifying its index within square brackets. All array indexes start at zero. For example,<br /> this statement assigns the value 28 to the second element of month_days.<br /> month_days[1] = 28;<br /> The next line displays the value stored at index 3.<br /> System.out.println(month_days[3]);<br /> Putting together all the pieces, here is a program that creates an array of the<br /> number of days in each month.<br /> // Demonstrate a one-dimensional array.<br /> class Array {</div> <div>THE JAVA LANGUAGE<br /> Chapter 11: Multithreaded Programming 305<br /> Suspending, Resuming, and Stopping Threads<br /> Sometimes, suspending execution of a thread is useful. For example, a separate thread<br /> can be used to display the time of day. If the user doesn’t want a clock, then its thread<br /> can be suspended. Whatever the case, suspending a thread is a simple matter. Once<br /> suspended, restarting the thread is also a simple matter.<br /> The mechanisms to suspend, stop, and resume threads differ between Java 2 and<br /> earlier versions. Although you should use the Java 2 approach for all new code, you<br /> still need to understand how these operations were accomplished for earlier Java<br /> environments. For example, you may need to update or maintain older, legacy code.<br /> You also need to understand why a change was made for Java 2. For these reasons, the<br /> next section describes the original way that the execution of a thread was controlled,<br /> followed by a section that describes the approach required for Java 2.<br /> Suspending, Resuming, and Stopping Threads Using<br /> Java 1.1 and Earlier<br /> Prior to Java 2, a program used suspend( ) and resume( ), which are methods defined by<br /> Thread,topause and restart the execution of a thread. They have the form shown below:<br /> final void suspend( )<br /> final void resume( )<br /> The following program demonstrates these methods:<br /> // Using suspend() and resume().<br /> class NewThread implements Runnable {<br /> String name; // name of thread<br /> Thread t;<br /> NewThread(String threadname) {<br /> name = threadname;<br /> t = new Thread(this, name);<br /> System.out.println("New thread: " + t);<br /> t.start(); // Start the thread<br /> }<br /> // This is the entry point for thread.<br /> public void run() {<br /> try {<br /> for(int i = 15; i > 0; i--) {<br /> System.out.println(name + ": " + i);<br /> Thread.sleep(200);</div> <div>564 Java™ 2: The Complete Reference<br /> Method<br /> abstract void close( )<br /> abstract void flush( )<br /> void write(int ch)<br /> void write(char buffer[ ])<br /> abstract void write(char buffer[ ],<br /> int offset,<br /> int numChars)<br /> void write(String str)<br /> void write(String str, int offset,<br /> int numChars)<br /> Description<br /> Closes the output stream. Further write<br /> attempts will generate an IOException.<br /> Finalizes the output state so that any<br /> buffers are cleared. That is, it flushes the<br /> output buffers.<br /> Writes a single character to the invoking<br /> output stream. Note that the parameter is<br /> an int, which allows you to call write with<br /> expressions without having to cast them<br /> back to char.<br /> Writes a complete array of characters to<br /> the invoking output stream.<br /> Writes a subrange of numChars characters<br /> from the array buffer, beginning at<br /> buffer[offset] to the invoking output stream.<br /> Writes str to the invoking output stream.<br /> Writes a subrange of numChars characters<br /> from the array str, beginning at the<br /> specified offset.<br /> Table 17-4.<br /> The Methods Defined by Writer<br /> The following example shows how to read lines from a file and print these<br /> to the standard output stream. It reads its own source file, which must be in the<br /> current directory.<br /> // Demonstrate FileReader.<br /> import java.io.*;<br /> class FileReaderDemo {<br /> public static void main(String args[]) throws Exception {<br /> FileReader fr = new FileReader("FileReaderDemo.java");<br /> BufferedReader br = new BufferedReader(fr);<br /> String s;</div> <div>THE JAVA LANGUAGE<br /> Chapter 3: Data Types, Variables, and Arrays 59<br /> Conversion of int to byte.<br /> i and b 257 1<br /> Conversion of double to int.<br /> d and i 323.142 323<br /> Conversion of double to byte.<br /> d and b 323.142 67<br /> Let’s look at each conversion. When the value 257 is cast into a byte variable, the<br /> result is the remainder of the division of 257 by 256 (the range of a byte), which is 1 in<br /> this case. When the d is converted to an int, its fractional component is lost. When d is<br /> converted to a byte, its fractional component is lost, and the value is reduced modulo<br /> 256, which in this case is 67.<br /> Automatic Type Promotion in Expressions<br /> In addition to assignments, there is another place where certain type conversions<br /> may occur: in expressions. To see why, consider the following. In an expression, the<br /> precision required of an intermediate value will sometimes exceed the range of either<br /> operand. For example, examine the following expression:<br /> byte a = 40;<br /> byte b = 50;<br /> byte c = 100;<br /> int d = a * b / c;<br /> The result of the intermediate term a * b easily exceeds the range of either of<br /> its byte operands. To handle this kind of problem, Java automatically promotes each<br /> byte or short operand to int when evaluating an expression. This means that the<br /> subexpression a * b is performed using integers—not bytes. Thus, 2,000, the result of<br /> the intermediate expression, 50 * 40, is legal even though a and b are both specified as<br /> type byte.<br /> As useful as the automatic promotions are, they can cause confusing compile-time<br /> errors. For example, this seemingly correct code causes a problem:<br /> byte b = 50;<br /> b = b * 2; // Error! Cannot assign an int to a byte!</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 27: Servlets 971<br /> HttpSessionEvent defines one method, getSession( ), which is shown here:<br /> HttpSession getSession( )<br /> It returns the session in which the event occurred.<br /> The HttpSessionBindingEvent Class<br /> The HttpSessionBindingEvent class extends HttpSessionEvent. It is generated<br /> when a listener is bound to or unbound from a value in an HttpSession object. It is<br /> also generated when an attribute is bound or unbound. Here are its constructors:<br /> HttpSessionBindingEvent(HttpSession session, String name)<br /> HttpSessionBindingEvent(HttpSession session, String name, Object val)<br /> Here, session is the source of the event and name is the name associated with the object<br /> that is being bound or unbound. If an attribute is being bound or unbound, its value is<br /> passed in val.<br /> The getName( ) method obtains the name that is being bound or unbound. Its is<br /> shown here:<br /> String getName( )<br /> The getSession( ) method, shown next, obtains the session to which the listener is<br /> being bound or unbound:<br /> HttpSession getSession( )<br /> The getValue( ) method obtains the value of the attribute that is being bound or<br /> unbound. It is shown here:<br /> Object getValue( )<br /> Handling HTTP Requests and Responses<br /> The HttpServlet class provides specialized methods that handle the various types of<br /> HTTP requests. A servlet developer typically overrides one of these methods. These<br /> methods are doDelete( ), doGet( ), doHead( ), doOptions( ), doPost( ), doPut( ), and<br /> doTrace( ). A complete description of the different types of HTTP requests is beyond<br /> the scope of this book. However, the GET and POST requests are commonly used<br /> when handling form input. Therefore, this section presents examples of these cases.<br /> Handling HTTP GET Requests<br /> Here we will develop a servlet that handles an HTTP GET request. The servlet is invoked<br /> when a form on a Web page is submitted. The example contains two files. A Web page</div> <div>THE JAVA LIBRARY<br /> Chapter 24: New I/O, Regular Expressions, and Other Packages 857<br /> public static void main(String args[]) {<br /> RandomAccessFile fOut;<br /> FileChannel fChan;<br /> ByteBuffer mBuf;<br /> try {<br /> fOut = new RandomAccessFile("test.txt", "rw");<br /> // Next, obtain a channel to that file.<br /> fChan = fOut.getChannel();<br /> // Then, map the file into a buffer.<br /> mBuf = fChan.map(FileChannel.MapMode.READ_WRITE,<br /> 0, 26);<br /> // Write some bytes to the buffer.<br /> for(int i=0; i<26; i++)<br /> mBuf.put((byte)('A' + i));<br /> }<br /> }<br /> // close channel and file.<br /> fChan.close();<br /> fOut.close();<br /> } catch (IOException exc) {<br /> System.out.println(exc);<br /> System.exit(1);<br /> }<br /> As you can see, there are no explicit write operations to the channel, itself. Because mBuf<br /> is mapped to the file, changes to mBuf are automatically reflected in the underlying file.<br /> Copying a File Using the New I/O<br /> The new I/O system simplifies some types of file operations. For example, the<br /> following program copies a file. It does so by opening an input channel to the source<br /> file and an output channel to the target file. It then writes the mapped input buffer<br /> to the output file in a single operation. You might want to compare this version of the<br /> file copy program to the one found in Chapter 12. As you will find, the part of the<br /> program that actually copies the file is substantially shorter.<br /> // Copy a file using NIO.</div> <div>THE JAVA LIBRARY<br /> Chapter 14: Exploring java.lang 421<br /> Method<br /> static double pow(double y, double x)<br /> static double sqrt(double arg)<br /> Description<br /> Returns y raised to the x; for example,<br /> pow(2.0, 3.0) returns 8.0.<br /> Returns the square root of arg.<br /> Rounding Functions<br /> The Math class defines several methods that provide various types of rounding<br /> operations. They are shown in Table 14-15.<br /> Method<br /> static int abs(int arg)<br /> static long abs(long arg)<br /> static float abs(float arg)<br /> static double abs(double arg)<br /> Description<br /> Returns the absolute value of arg.<br /> Returns the absolute value of arg.<br /> Returns the absolute value of arg.<br /> Returns the absolute value of arg.<br /> static double ceil(double arg)<br /> Returns the smallest whole number greater<br /> than or equal to arg.<br /> static double floor(double arg) Returns the largest whole number less than<br /> or equal to arg.<br /> static int max(int x, int y) Returns the maximum of x and y.<br /> static long max(long x, long y) Returns the maximum of x and y.<br /> static float max(float x, float y) Returns the maximum of x and y.<br /> static double max(double x, double y) Returns the maximum of x and y.<br /> static int min(int x, int y)<br /> Returns the minimum of x and y<br /> static long min(long x, long y) Returns the minimum of x and y.<br /> static float min(float x, float y) Returns the minimum of x and y.<br /> static double min(double x, double y) Returns the minimum of x and y.<br /> static double rint(double arg)<br /> Returns the integer nearest in value to arg.<br /> static int round(float arg)<br /> Returns arg rounded up to the nearest int.<br /> static long round(double arg) Returns arg rounded up to the nearest long.<br /> Table 14-15.<br /> The Rounding Methods Defined by Math</div> <div>736 Java™ 2: The Complete Reference<br /> This chapter continues our exploration of the Abstract Window Toolkit (AWT).<br /> It examines the standard controls and layout managers defined by Java. It also<br /> discusses menus and the menu bar. The chapter includes a discussion of two<br /> high-level components: the dialog box and the file dialog box. It concludes with<br /> another look at event handling.<br /> Controls are components that allow a user to interact with your application in<br /> various ways—for example, a commonly used control is the push button. A layout<br /> manager automatically positions components within a container. Thus, the appearance<br /> of a window is determined by a combination of the controls that it contains and the<br /> layout manager used to position them.<br /> In addition to the controls, a frame window can also include a standard-style menu bar.<br /> Each entry in a menu bar activates a drop-down menu of options from which the user can<br /> choose. A menu bar is always positioned at the top of a window. Although different in<br /> appearance, menu bars are handled in much the same way as are the other controls.<br /> While it is possible to manually position components within a window, doing so is<br /> quite tedious. The layout manager automates this task. For the first part of this chapter,<br /> which introduces the various controls, the default layout manager will be used. This<br /> displays components in a container using left-to-right, top-to-bottom organization.<br /> Once the controls have been covered, the layout managers will be examined. There<br /> you will see how to better manage the positioning of your controls.<br /> Control Fundamentals<br /> The AWT supports the following types of controls:<br /> ■ Labels<br /> ■ Push buttons<br /> ■ Check boxes<br /> ■ Choice lists<br /> ■ Lists<br /> ■ Scroll bars<br /> ■ Text editing<br /> These controls are subclasses of Component.<br /> Adding and Removing Controls<br /> To include a control in a window, you must add it to the window. To do this, you must<br /> first create an instance of the desired control and then add it to a window by calling add( ),</div> <div>768 Java™ 2: The Complete Reference<br /> "Therefore all progress depends " +<br /> "on the unreasonable man.\n\n" +<br /> " - George Bernard Shaw\n\n";<br /> }<br /> }<br /> add(new TextArea(msg), BorderLayout.CENTER);<br /> Sample output from the BorderLayoutDemo applet is shown here:<br /> Using Insets<br /> Sometimes you will want to leave a small amount of space between the container<br /> that holds your components and the window that contains it. To do this, override<br /> the getInsets( ) method that is defined by Container. This function returns an Insets<br /> object that contains the top, bottom, left, and right inset to be used when the container<br /> is displayed. These values are used by the layout manager to inset the components<br /> when it lays out the window. The constructor for Insets is shown here:<br /> Insets(int top, int left, int bottom, int right)<br /> The values passed in top, left, bottom, and right specify the amount of space between the<br /> container and its enclosing window.</div> <div>644 Java™ 2: The Complete Reference<br /> NAME NAME is an optional attribute used to specify a name for the applet instance.<br /> Applets must be named in order for other applets on the same page to find them by<br /> name and communicate with them. To obtain an applet by name, use getApplet( ),<br /> which is defined by the AppletContext interface.<br /> WIDTH AND HEIGHT WIDTH and HEIGHT are required attributes that give the<br /> size (in pixels) of the applet display area.<br /> ALIGN ALIGN is an optional attribute that specifies the alignment of the applet.<br /> This attribute is treated the same as the HTML IMG tag with these possible values:<br /> LEFT, RIGHT, TOP, BOTTOM, MIDDLE, BASELINE, TEXTTOP, ABSMIDDLE,<br /> and ABSBOTTOM.<br /> VSPACE AND HSPACE These attributes are optional. VSPACE specifies the space,<br /> in pixels, above and below the applet. HSPACE specifies the space, in pixels, on each<br /> side of the applet. They’re treated the same as the IMG tag’s VSPACE and HSPACE<br /> attributes.<br /> PARAM NAME AND VALUE The PARAM tag allows you to specify appletspecific<br /> arguments in an HTML page. Applets access their attributes with the<br /> getParameter( ) method.<br /> HANDLING OLDER BROWSERS Some very old web browsers can’t execute applets<br /> and don’t recognize the APPLET tag. Although these browsers are now nearly extinct<br /> (having been replaced by Java-compatible ones), you may need to deal with them<br /> occasionally. The best way to design your HTML page to deal with such browsers is to<br /> include HTML text and markup within your <applet></applet> tags. If the applet tags<br /> are not recognized by your browser, you will see the alternate markup. If Java is<br /> available, it will consume all of the markup between the <applet></applet> tags and<br /> disregard the alternate markup.<br /> Here’s the HTML to start an applet called SampleApplet in Java and to display a<br /> message in older browsers:<br /> <applet code="SampleApplet" width=200 height=40><br /> If you were driving a Java powered browser,<br /> you'd see "e;A Sample Applet"e; here.<p><br /> </applet><br /> Passing Parameters to Applets<br /> As just discussed, the APPLET tag in HTML allows you to pass parameters to your<br /> applet. To retrieve a parameter, use the getParameter( ) method. It returns the value of</div> <div>THE JAVA LIBRARY<br /> Chapter 16: java.util Part 2: More Utility Classes 515<br /> Calendar defines the following int constants, which are used when you get or set<br /> components of the calendar:<br /> AM FRIDAY PM<br /> AM_PM HOUR SATURDAY<br /> APRIL HOUR_OF_DAY SECOND<br /> AUGUST JANUARY SEPTEMBER<br /> DATE JULY SUNDAY<br /> DAY_OF_MONTH JUNE THURSDAY<br /> DAY_OF_WEEK MARCH TUESDAY<br /> DAY_OF_WEEK_IN_MONTH MAY UNDECIMBER<br /> DAY_OF_YEAR MILLISECOND WEDNESDAY<br /> DECEMBER MINUTE WEEK_OF_MONTH<br /> DST_OFFSET MONDAY WEEK_OF_YEAR<br /> ERA MONTH YEAR<br /> FEBRUARY NOVEMBER ZONE_OFFSET<br /> FIELD_COUNT<br /> OCTOBER<br /> Method<br /> abstract void add(int which, int val)<br /> boolean after(Object calendarObj)<br /> boolean before(Object calendarObj)<br /> Description<br /> Adds val to the time or date<br /> component specified by which. To<br /> subtract, add a negative value. which<br /> must be one of the fields defined by<br /> Calendar, such as Calendar.HOUR.<br /> Returns true if the invoking Calendar<br /> object contains a date that is later<br /> than the one specified by calendarObj.<br /> Otherwise, it returns false.<br /> Returns true if the invoking Calendar<br /> object contains a date that is earlier<br /> than the one specified by calendarObj.<br /> Otherwise, it returns false.<br /> Table 16-4.<br /> Commonly Used Methods Defined by Calendar</div> <div>80 Java™ 2: The Complete Reference<br /> }<br /> }<br /> int d;<br /> c = ++b;<br /> d = a++;<br /> c++;<br /> System.out.println("a = " + a);<br /> System.out.println("b = " + b);<br /> System.out.println("c = " + c);<br /> System.out.println("d = " + d);<br /> The output of this program follows:<br /> a = 2<br /> b = 3<br /> c = 4<br /> d = 1<br /> The Bitwise Operators<br /> Java defines several bitwise operators which can be applied to the integer types, long,<br /> int, short, char, and byte. These operators act upon the individual bits of their operands.<br /> They are summarized in the following table:<br /> Operator<br /> Result<br /> ~ Bitwise unary NOT<br /> &<br /> Bitwise AND<br /> | Bitwise OR<br /> ^<br /> Bitwise exclusive OR<br /> >> Shift right<br /> >>> Shift right zero fill<br /> << Shift left<br /> &=<br /> Bitwise AND assignment<br /> |= Bitwise OR assignment</div> <div>THE JAVA LIBRARY<br /> Chapter 23: Images 831<br /> }<br /> private int cont(int in) {<br /> return (in < 128) ? (int)(in/gain) : multclamp(in, gain);<br /> }<br /> public int filterRGB(int x, int y, int rgb) {<br /> int r = cont((rgb >> 16) & 0xff);<br /> int g = cont((rgb >> 8) & 0xff);<br /> int b = cont(rgb & 0xff);<br /> return (0xff000000 | r << 16 | g << 8 | b);<br /> }<br /> Figure 23-10 shows the image after Contrast is pressed.<br /> Convolver.java<br /> The abstract class Convolver handles the basics of a convolution filter by implementing<br /> the ImageConsumer interface to move the source pixels into an array called imgpixels.<br /> It also creates a second array called newimgpixels for the filtered data. Convolution<br /> filters sample a small rectangle of pixels around each pixel in an image, called the<br /> Figure 23-10.<br /> Using the Contrast filter with ImageFilterDemo</div> <div>THE JAVA LIBRARY<br /> Chapter 18: Networking 619<br /> int fsp = request.indexOf(' ');<br /> int nsp = request.indexOf(' ', fsp+1);<br /> int eol = request.indexOf('\n');<br /> String method = request.substring(0, fsp);<br /> String url = request.substring(fsp+1, nsp);<br /> String raw_mime_header = request.substring(eol + 1);<br /> MimeHeader inmh = new MimeHeader(raw_mime_header);<br /> request = request.substring(0, eol);<br /> }<br /> if (method.equalsIgnoreCase("get")) {<br /> if (url.indexOf("://") >= 0) {<br /> handleProxy(out, url, inmh);<br /> } else {<br /> handleGet(out, url, inmh);<br /> }<br /> } else {<br /> writeString(out, error(405, "Method Not Allowed", method));<br /> }<br /> in.close();<br /> out.close();<br /> public void run() {<br /> try {<br /> ServerSocket acceptSocket;<br /> acceptSocket = new ServerSocket(port);<br /> while (true) {<br /> Socket s = acceptSocket.accept();<br /> host = s.getInetAddress().getHostName();<br /> doRequest(s);<br /> s.close();<br /> }<br /> } catch (IOException e) {<br /> log.log("accept loop IOException: " + e + "\n");<br /> } catch (Exception e) {<br /> log.log("Exception: " + e);<br /> }<br /> }<br /> private Thread t;<br /> public synchronized void start() {</div> <div>930 Java™ 2: The Complete Reference<br /> Check Boxes<br /> The JCheckBox class, which provides the functionality of a check box, is a concrete<br /> implementation of AbstractButton. Its immediate superclass is JToggleButton, which<br /> provides support for two-state buttons. Some of its constructors are shown here:<br /> JCheckBox(Icon i)<br /> JCheckBox(Icon i, boolean state)<br /> JCheckBox(String s)<br /> JCheckBox(String s, boolean state)<br /> JCheckBox(String s, Icon i)<br /> JCheckBox(String s, Icon i, boolean state)<br /> Here, i is the icon for the button. The text is specified by s. If state is true, the check box<br /> is initially selected. Otherwise, it is not.<br /> The state of the check box can be changed via the following method:<br /> void setSelected(boolean state)<br /> Here, state is true if the check box should be checked.<br /> The following example illustrates how to create an applet that displays four check<br /> boxes and a text field. When a check box is pressed, its text is displayed in the text field.<br /> The content pane for the JApplet object is obtained, and a flow layout is assigned as its<br /> layout manager. Next, four check boxes are added to the content pane, and icons are<br /> assigned for the normal, rollover, and selected states. The applet is then registered to<br /> receive item events. Finally, a text field is added to the content pane.<br /> When a check box is selected or deselected, an item event is generated. This is<br /> handled by itemStateChanged( ). Inside itemStateChanged( ), the getItem( ) method<br /> gets the JCheckBox object that generated the event. The getText( ) method gets the text<br /> for that check box and uses it to set the text inside the text field.<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import javax.swing.*;<br /> /*<br /> <applet code="JCheckBoxDemo" width=400 height=50><br /> </applet><br /> */<br /> public class JCheckBoxDemo extends JApplet<br /> implements ItemListener {<br /> JTextField jtf;<br /> public void init() {</div> <div>THE JAVA LIBRARY<br /> Chapter 21: Introducing the AWT: Working with Windows, Graphics, and Text 697<br /> Handling Events in a Frame Window<br /> Since Frame is a subclass of Component, it inherits all the capabilities defined by<br /> Component. This means that you can use and manage a frame window that you create<br /> just like you manage your applet’s main window. For example, you can override<br /> paint( ) to display output, call repaint( ) when you need to restore the window, and<br /> override all event handlers. Whenever an event occurs in a window, the event handlers<br /> defined by that window will be called. Each window handles its own events. For<br /> example, the following program creates a window that responds to mouse events.<br /> The main applet window also responds to mouse events. When you experiment<br /> with this program, you will see that mouse events are sent to the window in which<br /> the event occurs.<br /> // Handle mouse events in both child and applet windows.<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import java.applet.*;<br /> /*<br /> <applet code="WindowEvents" width=300 height=50><br /> </applet><br /> */<br /> // Create a subclass of Frame.<br /> class SampleFrame extends Frame<br /> implements MouseListener, MouseMotionListener {<br /> String msg = "";<br /> int mouseX=10, mouseY=40;<br /> int movX=0, movY=0;</div> <div>894 Java™ 2: The Complete Reference<br /> Updating an Existing JAR File<br /> The following command adds the file file1.class to Xyz.jar:<br /> jar -uf Xyz.jar file1.class<br /> Recursing Directories<br /> The following command adds all files below directoryX to Xyz.jar:<br /> jar -uf Xyz.jar -C directoryX *<br /> Introspection<br /> Introspection is the process of analyzing a Bean to determine its capabilities. This is an<br /> essential feature of the Java Beans API, because it allows an application builder tool to<br /> present information about a component to a software designer. Without introspection,<br /> the Java Beans technology could not operate.<br /> There are two ways in which the developer of a Bean can indicate which of its<br /> properties, events, and methods should be exposed by an application builder tool. With<br /> the first method, simple naming conventions are used. These allow the introspection<br /> mechanisms to infer information about a Bean. In the second way, an additional class is<br /> provided that explicitly supplies this information. The first approach is examined here.<br /> The second method is described later.<br /> The following sections indicate the design patterns for properties and events that<br /> enable the functionality of a Bean to be determined.<br /> Design Patterns for Properties<br /> A property is a subset of a Bean’s state. The values assigned to the properties determine<br /> the behavior and appearance of that component. This section discusses three types of<br /> properties: simple, Boolean, and indexed.<br /> Simple Properties<br /> A simple property has a single value. It can be identified by the following design<br /> patterns, where N is the name of the property and T is its type.<br /> public T getN( );<br /> public void setN(T arg);<br /> A read/write property has both of these methods to access its values. A read-only<br /> property has only a get method. A write-only property has only a set method.</div> <div>996 Java™ 2: The Complete Reference<br /> }<br /> // Return next integer in list.<br /> int getNext() {<br /> if(getIndex >= 100) {<br /> cout << "List Underflow";<br /> exit(1);<br /> }<br /> getIndex++;<br /> return storage[getIndex-1];<br /> }<br /> // Put an integer on the list.<br /> void putOnList(int i) {<br /> if(putIndex < 100) {<br /> storage[putIndex] = i;<br /> putIndex++;<br /> }<br /> else {<br /> cout << "List Overflow";<br /> exit(1);<br /> }<br /> }<br /> };<br /> int main()<br /> {<br /> IntArray nums;<br /> int i;<br /> for(i=0; i<10; i++) nums.putOnList(i);<br /> for(i=0; i<10; i++)<br /> cout << nums.getNext() << endl;<br /> return 0;<br /> }</div> <div>1154 Java™ 2: The Complete Reference<br /> Trees, Swing, 941–946<br /> TreeSet class, 449, 455, 456–457, 504<br /> TreePath class, 942<br /> trim( ), 365–366<br /> trimToSize( ), 451<br /> true, 39, 48, 51, 91<br /> TRUE, 401<br /> True and false in Java, 51, 91<br /> try block(s), 250, 253–254<br /> nested, 257–259<br /> Two's complement, 81<br /> TYPE, 382, 387, 398, 401, 402<br /> Type<br /> casting, 57–59, 60<br /> checking, 42<br /> conversion, automatic, 42,<br /> 57, 157–159<br /> promotion, 44, 59–61<br /> Types, data. See Data types<br /> U<br /> UDP protocol, 589, 591–592, 624<br /> UnavailableException class, 955,<br /> 960<br /> unhand( ) macro, 342<br /> UnicastRemoteObject, 874<br /> Unicode, 47, 48, 51, 315, 350, 356,<br /> 401, 562<br /> Uniform Resource Identifier<br /> (URI), 626<br /> UNIX, 5, 588<br /> UnknownHostException,<br /> 593, 595<br /> unmodifiable, 475<br /> unread( ), 558, 571<br /> UnsupportedOperationException,<br /> 266, 442–443, 445, 463, 475<br /> update( ), 527, 528, 638, 639, 705<br /> overriding, 635<br /> URI class, 592, 626<br /> URL (Uniform Resource<br /> Locator), 597<br /> specification format, 597<br /> URL class, 597–599, 601<br /> URLConnection class, 599–601<br /> User Datagram Protocol (UDP),<br /> 589, 591–592, 624<br /> V<br /> valueBound( ), 967<br /> valueOf( ), 353, 366–367<br /> values( ), 464<br /> valueUnbound( ), 967<br /> van Hoff, Arthur, 7<br /> Variable(s), 52–56<br /> declaration, 30–31, 52–53<br /> definition of, 29, 52<br /> dynamic initialization of, 53<br /> final, 178–179<br /> instance. See Instance<br /> variables<br /> interface, 236<br /> object reference. See Object<br /> reference variables<br /> scope and lifetime of, 54–56<br /> Vector class, 462, 485–490<br /> methods, table of, 486–488<br /> Virtual functions (C++), 213<br /> Virtual machine, Java, 400<br /> void, 28, 138<br /> Void class, 401<br /> volatile modifier, 291–292, 331, 332<br /> VSPACE 644<br /> W<br /> wait( ), 221, 297–298, 300–302<br /> waitFor( ), 407<br /> Warth, Chris, 7<br /> wc( ), 572–577<br /> WeakHashMap class, 466, 467<br /> Web browser<br /> executing applet in, 330,<br /> 331, 628<br /> handling older, 644<br /> using status window of, 642<br /> Web server and servlets, 950, 951<br /> while loop, 109–111<br /> Whitespace, 37<br /> from string, removing, 365<br /> whitespaceChars( ), 575<br /> Whois, 596–597<br /> WIDTH, 644<br /> Window<br /> displaying information in,<br /> 704–705<br /> frame. See Frame window<br /> fundamentals, 691–693<br /> status, using, 642<br /> Window class, 693, 783<br /> windowActivated( ), 672<br /> windowClosed( ), 672<br /> windowClosing( ), 672, 694, 695<br /> windowDeactivated( ), 672<br /> windowDeiconified( ), 672<br /> WindowEvent class, 658, 667–668<br /> WindowFocusListener interface,<br /> 669, 672<br /> windowGainedFocus( ), 672<br /> windowIconified( ), 672<br /> WindowListener interface, 669,<br /> 672, 694<br /> windowLostFocus( ), 672<br /> windowOpened( ), 672<br /> Windows 3.1 and Java, 26<br /> Windows 95/98 and Windows NT<br /> and Java, 26<br /> wordChars( ), 575<br /> World Wide Web, 7, 8, 597<br /> wrap( ), 850<br /> Wrappers, simple type, 380–401<br /> write( ), 315, 322–323, 326–328, 850,<br /> 855–856<br /> Writer class, 315, 545, 562<br /> methods defined by, table<br /> of, 564<br /> writeObject( ), 578<br /> writeTo( ), 554<br /> X<br /> XOR (exclusive OR) operator (^)<br /> bitwise, 80, 82, 83<br /> Boolean, 92<br /> Y<br /> Yellin, Frank, 7<br /> Z<br /> Zero crossing, 81<br /> ZIP file format, 536<br /> ZLIB file format, 536</div> <div>THE JAVA LIBRARY<br /> Chapter 23: Images 837<br /> Figure 23-12.<br /> Using the Sharpen filter with ImageFilterDemo<br /> Cell Animation<br /> Now that we have presented an overview of the image APIs, we can put together<br /> an interesting applet that will display a sequence of animation cells. The animation<br /> cells are taken from a single image that can arrange the cells in a grid specified via<br /> the rows and cols <param> tags. Each cell in the image is snipped out in a way similar<br /> to that used in the TileImage example earlier. We obtain the sequence in which to<br /> display the cells from the sequence <param> tag. This is a comma-separated list of<br /> cell numbers that is zero-based and proceeds across the grid from left to right, top<br /> to bottom.<br /> Once the applet has parsed the <param> tags and loaded the source image, it cuts<br /> the image into a number of small subimages. Then, a thread is started that causes the<br /> images to be displayed according to the order described in sequence. The thread sleeps<br /> for enough time to maintain the framerate. Here is the source code:<br /> // Animation example.<br /> import java.applet.*;<br /> import java.awt.*;</div> <div>THE JAVA LIBRARY<br /> Chapter 14: Exploring java.lang 427<br /> Method<br /> int activeCount( )<br /> int activeGroupCount( )<br /> final void checkAccess( )<br /> final void destroy( )<br /> int enumerate(Thread group[ ])<br /> int enumerate(Thread group[ ], boolean all)<br /> int enumerate(ThreadGroup group[ ])<br /> int enumerate(ThreadGroup group[ ],<br /> boolean all)<br /> final int getMaxPriority( )<br /> Description<br /> Returns the number of threads in<br /> the group plus any groups for<br /> which this thread is a parent.<br /> Returns the number of groups<br /> for which the invoking thread<br /> is a parent.<br /> Causes the security manager to<br /> verify that the invoking thread<br /> may access and/or change the<br /> group on which checkAccess( )<br /> is called.<br /> Destroys the thread group<br /> (and any child groups) on which<br /> it is called.<br /> The threads that comprise the<br /> invoking thread group are put into<br /> the group array.<br /> The threads that comprise the<br /> invoking thread group are put into<br /> the group array. If all is true, then<br /> threads in all subgroups of the<br /> thread are also put into group.<br /> The subgroups of the invoking<br /> thread group are put into the<br /> group array.<br /> The subgroups of the invoking<br /> thread group are put into the group<br /> array. If all is true, then all<br /> subgroups of the subgroups (and<br /> so on) are also put into group.<br /> Returns the maximum priority<br /> setting for the group.<br /> Table 14-17.<br /> The Methods Defined by ThreadGroup</div> <div>This page intentionally left blank.</div> <div>THE JAVA LANGUAGE<br /> Chapter 5: Control Statements 101<br /> Here, if a is less than b, then a is set to zero. Otherwise, b is set to zero. In no case are<br /> they both set to zero.<br /> Most often, the expression used to control the if will involve the relational operators.<br /> However, this is not technically necessary. It is possible to control the if using a single<br /> boolean variable, as shown in this code fragment:<br /> boolean dataAvailable;<br /> // ...<br /> if (dataAvailable)<br /> ProcessData();<br /> else<br /> waitForMoreData();<br /> Remember, only one statement can appear directly after the if or the else. If you<br /> want to include more statements, you’ll need to create a block, as in this fragment:<br /> int bytesAvailable;<br /> // ...<br /> if (bytesAvailable > 0) {<br /> ProcessData();<br /> bytesAvailable -= n;<br /> } else<br /> waitForMoreData();<br /> Here, both statements within the if block will execute if bytesAvailable is greater<br /> than zero.<br /> Some programmers find it convenient to include the curly braces when using the if,<br /> even when there is only one statement in each clause. This makes it easy to add another<br /> statement at a later date, and you don’t have to worry about forgetting the braces. In<br /> fact, forgetting to define a block when one is needed is a common cause of errors. For<br /> example, consider the following code fragment:<br /> int bytesAvailable;<br /> // ...<br /> if (bytesAvailable > 0) {<br /> ProcessData();<br /> bytesAvailable -= n;<br /> } else<br /> waitForMoreData();<br /> bytesAvailable = n;</div> <div>THE JAVA LANGUAGE<br /> Chapter 12: I/O, Applets, and Other Topics 333<br /> Here, object is an instance of a class, and type is a class type. If object is of the specified<br /> type or can be cast into the specified type, then the instanceof operator evaluates to<br /> true. Otherwise, its result is false. Thus, instanceof is the means by which your<br /> program can obtain run-time type information about an object.<br /> The following program demonstrates instanceof:<br /> // Demonstrate instanceof operator.<br /> class A {<br /> int i, j;<br /> }<br /> class B {<br /> int i, j;<br /> }<br /> class C extends A {<br /> int k;<br /> }<br /> class D extends A {<br /> int k;<br /> }<br /> class InstanceOf {<br /> public static void main(String args[]) {<br /> A a = new A();<br /> B b = new B();<br /> C c = new C();<br /> D d = new D();<br /> if(a instanceof A)<br /> System.out.println("a is instance of A");<br /> if(b instanceof B)<br /> System.out.println("b is instance of B");<br /> if(c instanceof C)<br /> System.out.println("c is instance of C");<br /> if(c instanceof A)<br /> System.out.println("c can be cast to A");<br /> if(a instanceof C)<br /> System.out.println("a can be cast to C");</div> <div>818 Java™ 2: The Complete Reference<br /> Figure 23-5.<br /> Sample output from MemoryImageGenerator<br /> ImageProducer, described earlier. An object that implements the ImageConsumer<br /> interface is going to create int or byte arrays that represent pixels from an Image<br /> object. We will examine the PixelGrabber class, which is a simple implementation of<br /> the ImageConsumer interface.<br /> PixelGrabber<br /> The PixelGrabber class is defined within java.lang.image. It is the inverse of the<br /> MemoryImageSource class. Rather than constructing an image from an array of<br /> pixel values, it takes an existing image and grabs the pixel array from it. To use<br /> PixelGrabber, you first create an array of ints big enough to hold the pixel data, and<br /> then you create a PixelGrabber instance passing in the rectangle that you want to grab.<br /> Finally, you call grabPixels( ) on that instance.<br /> The PixelGrabber constructor that is used in this chapter is shown here:<br /> PixelGrabber(Image imgObj, int left, int top, int width, int height, int pixel[ ],<br /> int offset, int scanLineWidth)<br /> Here, imgObj is the object whose pixels are being grabbed. The values of left and top<br /> specify the upper-left corner of the rectangle, and width and height specify the</div> <div>404 Java™ 2: The Complete Reference<br /> Method<br /> void exit(int exitCode)<br /> long freeMemory( )<br /> void gc( )<br /> static Runtime getRuntime( )<br /> void halt(int code)<br /> void load(String libraryFileName)<br /> void loadLibrary(String libraryName)<br /> boolean removeShutdownHook(Thread thrd)<br /> void runFinalization( )<br /> long totalMemory( )<br /> void traceInstructions(boolean traceOn)<br /> void traceMethodCalls(boolean traceOn)<br /> Description<br /> Halts execution and returns the value of<br /> exitCode to the parent process. By<br /> convention, 0 indicates normal<br /> termination. All other values indicate<br /> some form of error.<br /> Returns the approximate number of bytes<br /> of free memory available to the Java<br /> run-time system.<br /> Initiates garbage collection.<br /> Returns the current Runtime object.<br /> Immediately terminates the Java virtual<br /> machine. No termination threads or<br /> finalizers are run. The value of code is<br /> returned to the invoking process.<br /> (Added by Java 2, version 1.3)<br /> Loads the dynamic library whose file is<br /> specified by libraryFileName, which must<br /> specify its complete path.<br /> Loads the dynamic library whose name is<br /> associated with libraryName.<br /> Removes thrd from the list of threads<br /> to run when the Java virtual machine<br /> terminates. It returns true if<br /> successful⎯that is, if the thread was<br /> removed. (Added by Java 2, verison 1.3)<br /> Initiates calls to the finalize( ) methods of<br /> unused but not yet recycled objects.<br /> Returns the total number of bytes of<br /> memory available to the program.<br /> Turns on or off instruction tracing,<br /> depending upon the value of traceOn. If<br /> traceOn is true, the trace is displayed. If it<br /> is false, tracing is turned off.<br /> Turns on or off method call tracing,<br /> depending upon the value of traceOn. If<br /> traceOn is true, the trace is displayed. If it<br /> is false, tracing is turned off.<br /> Table 14-10.<br /> The Commonly Used Methods Defined by Runtime (continued)</div> <div>920 Java™ 2: The Complete Reference<br /> Figure 25-14.<br /> The Bean Builder application executing<br /> You can save your application by selecting Save in the file menu.<br /> The Bean Builder is a powerful, yet easy to use development tool. If Bean<br /> development is in your future, you will want to master its features. The best way<br /> to do this is to create a number of sample Bean applications. Also, try creating your<br /> own Beans and loading them into the palette. (To do so, create a JAR file containing<br /> your Beans, as described earlier.)</div> <div>THE JAVA LIBRARY<br /> Chapter 16: java.util Part 2: More Utility Classes 533<br /> void schedule(TimerTask TTask,<br /> Date targetTime)<br /> void schedule(TimerTask TTask,<br /> Date targetTime,<br /> long repeat)<br /> void scheduleAtFixedRate(<br /> TimerTask TTask,<br /> long wait, long repeat)<br /> void scheduleAtFixedRate(<br /> TimerTask TTask,<br /> Date targetTime,<br /> long repeat)<br /> TTask is scheduled for execution at the<br /> time specified by targetTime.<br /> TTask is scheduled for execution at the<br /> time specified by targetTime. The task is<br /> then executed repeatedly at the interval<br /> passed in repeat. The repeat parameter is<br /> specified in milliseconds.<br /> TTask is scheduled for execution after<br /> the period passed in wait has elapsed.<br /> The task is then executed repeatedly at<br /> the interval specified by repeat. Both wait<br /> and repeat are specified in milliseconds.<br /> The time of each repetition is relative to<br /> the first execution, not the preceding<br /> execution. Thus, the overall rate of<br /> execution is fixed.<br /> TTask is scheduled for execution at the<br /> time specified by targetTime. The task is<br /> then executed repeatedly at the interval<br /> passed in repeat. The repeat parameter is<br /> specified in milliseconds. The time of<br /> each repetition is relative to the first<br /> execution, not the preceding execution.<br /> Thus, the overall rate of execution<br /> is fixed.<br /> Table 16-9.<br /> The Methods Defined by Timer (continued)<br /> Once a Timer has been created, you will schedule a task by calling schedule( )<br /> on the Timer that you created. As Table 16-9 shows, there are several forms of<br /> schedule( ) which allow you to schedule tasks in a variety of ways.<br /> If you create a non-daemon task, then you will want to call cancel( ) to end the task<br /> when your program ends. If you don’t do this, then your program may “hang” for a<br /> period of time.<br /> The following program demonstrates Timer and TimerTask. It defines a timer<br /> task whose run( ) method displays the message “Timer task executed.” This task is<br /> scheduled to run once very half second after an intial delay of one second.</div> <div>602 Java™ 2: The Complete Reference<br /> ServerSocket has a method called accept( ), which is a blocking call that will wait<br /> for a client to initiate communications, and then return with a normal Socket that is<br /> then used for communication with the client.<br /> Java 2, version 1.4 added the getChannel( ) method to ServerSocket. This method<br /> returns a channel connected to the ServerSocket object. Channels are used by the new<br /> I/O classes contained in java.nio. (See Chapter 24.)<br /> A Caching Proxy HTTP Server<br /> In the remainder of this section, we will develop a simple caching proxy HTTP server,<br /> called http, to demonstrate client and server sockets. http supports only GET<br /> operations and a very limited range of hard-coded MIME types. (MIME types are the<br /> type descriptors for multimedia content.) The proxy HTTP server is single threaded, in<br /> that each request is handled in turn while all others wait. It has fairly naive strategies<br /> for caching—it keeps everything in RAM forever. When it is acting as a proxy server,<br /> http also copies every file it gets to a local cache for which it has no strategy for<br /> refreshing or garbage collecting. All of these caveats aside, http represents a productive<br /> example of client and server sockets, and it is fun to explore and easy to extend.<br /> Source Code<br /> The implementation of this HTTP server is presented here in five classes and one<br /> interface. A more complete implementation would likely split many of the methods<br /> out of the main class, httpd, in order to abstract more of the components. For space<br /> considerations in this book, most of the functionality is in the single class, and the small<br /> support classes are only acting as data structures. We will take a close look at each class<br /> and method to examine how this server works, starting with the support classes and<br /> ending with the main program.<br /> MimeHeader.java<br /> MIME is an Internet standard for communicating multimedia content over e-mail<br /> systems. This standard was created by Nat Borenstein in 1992. The HTTP protocol uses<br /> and extends the notion of MIME headers to pass general attribute/value pairs between<br /> the HTTP client and server.<br /> CONSTRUCTORS This class is a subclass of Hashtable so that it can conveniently<br /> store and retrieve the key/value pairs associated with a MIME header. It has two<br /> constructors. One creates a blank MimeHeader with no keys. The other takes a string<br /> formatted as a MIME header and parses it for the initial contents of the object. See<br /> parse( ) next.<br /> parse( ) The parse( ) method is used to take a raw MIME-formatted string and enter<br /> its key/value pairs into a given instance of MimeHeader. It uses a StringTokenizer to<br /> split the input data into individual lines, marked by the CRLF (\r\n) sequence. It then</div> <div>THE JAVA LIBRARY<br /> Chapter 14: Exploring java.lang 395<br /> Method<br /> static long parseLong(String str)<br /> throws NumberFormatException<br /> static long parseLong(String str, int radix)<br /> throws NumberFormatException<br /> short shortValue( )<br /> static String toBinaryString(long num)<br /> static String toHexString(long num)<br /> static String toOctalString(long num)<br /> String toString( )<br /> static String toString(long num)<br /> static String toString(long num, int radix)<br /> static Long valueOf(String str)<br /> throws NumberFormatException<br /> static Long valueOf(String str, int radix)<br /> throws NumberFormatException<br /> Description<br /> Returns the long equivalent of<br /> the number contained in the<br /> string specified by str in radix 10.<br /> Returns the long equivalent of<br /> the number contained in the<br /> string specified by str using the<br /> specified radix.<br /> Returns the value of the invoking<br /> object as a short.<br /> Returns a string that contains the<br /> binary equivalent of num.<br /> Returns a string that contains the<br /> hexadecimal equivalent of num.<br /> Returns a string that contains the<br /> octal equivalent of num.<br /> Returns a string that contains the<br /> decimal equivalent of the<br /> invoking object.<br /> Returns a string that contains the<br /> decimal equivalent of num.<br /> Returns a string that contains the<br /> decimal equivalent of num using<br /> the specified radix.<br /> Returns a Long object that<br /> contains the value specified by<br /> the string in str.<br /> Returns a Long object that<br /> contains the value specified by<br /> the string in str using the<br /> specified radix.<br /> Table 14-6.<br /> The Methods Defined by Long (continued)</div> <div>Complete References<br /> Herbert Schildt<br /> 0-07-213485-2<br /> Jeffery R. Shapiro<br /> 0-07-213381-3<br /> Chris H. Pappas & William<br /> H. Murray, III<br /> 0-07-212958-1<br /> Herbert Schildt<br /> 0-07-213084-9<br /> Ron Ben-Natan & Ori Sasson<br /> 0-07-222394-4<br /> Arthur Griffith<br /> 0-07-222405-3<br /> For the answers to everything related to your technology, drill as deeply as you<br /> please into our Complete Reference series. Written by topical authorities, these<br /> comprehensive resources offer a full range of knowledge, including extensive product<br /> information, theory, step-by-step tutorials, sample projects, and helpful appendixes.<br /> For more information on these and other Osborne books, visit our Web site at www.osborne.com</div> <div>904 Java™ 2: The Complete Reference<br /> Here, the first argument is the name of the property, and the second argument is the<br /> class of the Bean.<br /> // A Bean information class.<br /> package sunw.demo.colors;<br /> import java.beans.*;<br /> public class ColorsBeanInfo extends SimpleBeanInfo {<br /> public PropertyDescriptor[] getPropertyDescriptors() {<br /> try {<br /> PropertyDescriptor rectangular = new<br /> PropertyDescriptor("rectangular", Colors.class);<br /> PropertyDescriptor pd[] = {rectangular};<br /> return pd;<br /> }<br /> catch(Exception e) {<br /> }<br /> return null;<br /> }<br /> }<br /> You must compile this file from the BDK\demo directory or set CLASSPATH so<br /> that it includes c:\bdk\demo. If you don’t, the compiler won’t find the Colors.class<br /> file properly. After this file is successfully compiled, the colors.mft file can be updated,<br /> as shown here:<br /> Name: sunw/demo/colors/ColorsBeanInfo.class<br /> Name: sunw/demo/colors/Colors.class<br /> Java-Bean: True<br /> Use the JAR tool to create a new colors.jar file. Restart the BDK and create an<br /> instance of the Colors Bean in the BeanBox.<br /> The introspection facilities are designed to look for a BeanInfo class. If it exists,<br /> its behavior explicitly determines the information that is presented to a Bean user.<br /> Otherwise, design patterns are used to infer this information.<br /> Figure 25-5 shows how the Properties window now appears. Compare it with<br /> Figure 24-3. You can see that the properties inherited from Component are no longer<br /> presented for the Colors Bean. Only the rectangular property appears.</div> <div>Part IV<br /> Applying Java</div> <div>THE JAVA LIBRARY<br /> Chapter 13: String Handling 363<br /> lastIndexOf(t) = 65<br /> indexOf(the) = 7<br /> lastIndexOf(the) = 55<br /> indexOf(t, 10) = 11<br /> lastIndexOf(t, 60) = 55<br /> indexOf(the, 10) = 44<br /> lastIndexOf(the, 60) = 55<br /> Modifying a String<br /> Because String objects are immutable, whenever you want to modify a String, you<br /> must either copy it into a StringBuffer or use one of the following String methods,<br /> which will construct a new copy of the string with your modifications complete.<br /> substring( )<br /> You can extract a substring using substring( ). It has two forms. The first is<br /> String substring(int startIndex)<br /> Here, startIndex specifies the index at which the substring will begin. This form returns a<br /> copy of the substring that begins at startIndex and runs to the end of the invoking string.<br /> The second form of substring( ) allows you to specify both the beginning and<br /> ending index of the substring:<br /> String substring(int startIndex, int endIndex)<br /> Here, startIndex specifies the beginning index, and endIndex specifies the stopping<br /> point. The string returned contains all the characters from the beginning index, up to,<br /> but not including, the ending index.<br /> The following program uses substring( ) to replace all instances of one substring<br /> with another within a string:<br /> // Substring replacement.<br /> class StringReplace {<br /> public static void main(String args[]) {<br /> String org = "This is a test. This is, too.";<br /> String search = "is";<br /> String sub = "was";<br /> String result = "";<br /> int i;<br /> do { // replace all matching substrings<br /> System.out.println(org);</div> <div>976 Java™ 2: The Complete Reference<br /> public class AddCookieServlet extends HttpServlet {<br /> public void doPost(HttpServletRequest request,<br /> HttpServletResponse response)<br /> throws ServletException, IOException {<br /> // Get parameter from HTTP request.<br /> String data = request.getParameter("data");<br /> // Create cookie.<br /> Cookie cookie = new Cookie("MyCookie", data);<br /> // Add cookie to HTTP response.<br /> response.addCookie(cookie);<br /> }<br /> }<br /> // Write output to browser.<br /> response.setContentType("text/html");<br /> PrintWriter pw = response.getWriter();<br /> pw.println("<B>MyCookie has been set to");<br /> pw.println(data);<br /> pw.close();<br /> The source code for GetCookiesServlet.java is shown in the following listing. It<br /> invokes the getCookies( ) method to read any cookies that are included in the HTTP<br /> GET request. The names and values of these cookies are then written to the HTTP<br /> response. Observe that the getName( ) and getValue( ) methods are called to obtain<br /> this information.<br /> import java.io.*;<br /> import javax.servlet.*;<br /> import javax.servlet.http.*;<br /> public class GetCookiesServlet extends HttpServlet {<br /> public void doGet(HttpServletRequest request,<br /> HttpServletResponse response)<br /> throws ServletException, IOException {<br /> // Get cookies from header of HTTP request.</div> <div>690 Java™ 2: The Complete Reference<br /> Class<br /> GraphicsEnvironment<br /> GridBagConstraints<br /> GridBagLayout<br /> GridLayout<br /> Image<br /> Insets<br /> Label<br /> List<br /> MediaTracker<br /> Menu<br /> MenuBar<br /> MenuComponent<br /> MenuItem<br /> MenuShortcut<br /> Panel<br /> Point<br /> Polygon<br /> PopupMenu<br /> PrintJob<br /> Rectangle<br /> Robot<br /> Scrollbar<br /> Description<br /> Describes the collection of available Font and<br /> GraphicsDevice objects.<br /> Defines various constraints relating to the<br /> GridBagLayout class.<br /> The grid bag layout manager. Grid bag layout<br /> displays components subject to the constraints<br /> specified by GridBagConstraints.<br /> The grid layout manager. Grid layout displays<br /> components in a two-dimensional grid.<br /> Encapsulates graphical images.<br /> Encapsulates the borders of a container.<br /> Creates a label that displays a string.<br /> Creates a list from which the user can choose. Similar<br /> to the standard Windows list box.<br /> Manages media objects.<br /> Creates a pull-down menu.<br /> Creates a menu bar.<br /> An abstract class implemented by various menu<br /> classes.<br /> Creates a menu item.<br /> Encapsulates a keyboard shortcut for a menu item.<br /> The simplest concrete subclass of Container.<br /> Encapsulates a Cartesian coordinate pair, stored in x<br /> and y.<br /> Encapsulates a polygon.<br /> Encapsulates a pop-up menu.<br /> An abstract class that represents a print job.<br /> Encapsulates a rectangle.<br /> Supports automated testing of AWT- based applications.<br /> (Added by Java 2, vl.3)<br /> Creates a scroll bar control.<br /> Table 21-1.<br /> Some AWT Classes (continued)</div> <div>1062 Java™ 2: The Complete Reference<br /> column with rectangles in the Color of the appropriate pixel, using color( ). The bulb<br /> image strip is then painted over the new column. Then the current scrolled position,<br /> scrollX, is updated to be one more to the right, modulo the width, pixscan.<br /> start( ), stop( ), and run( )<br /> When the applet starts, it creates and starts a new Thread called t. This thread will call<br /> run( ), which will keep calling paint( ) as fast as possible, while maintaining the courtesy<br /> of calling yield( ) so that other threads can run. When the applet stop( ) method is<br /> called, stopFlag is set to true. This variable is checked by the infinite loop in the run( )<br /> method. Program control breaks from the loop when stopFlag is true.<br /> A useful enhancement would be to introduce a threshold frame rate, say 30 fps (frames<br /> per second), and change the call to the yield( ) into an appropriate call to sleep( ) if the<br /> rendering is too fast.<br /> The Code<br /> Here is the source code for the Lavatron class:<br /> import java.applet.*;<br /> import java.awt.* ;<br /> import java.awt.image.* ;<br /> public class Lavatron extends Applet implements Runnable {<br /> int scrollX;<br /> int bulbsW, bulbsH;<br /> int bulbS = 8;<br /> Dimension d;<br /> Image offscreen, bulb, img;<br /> Graphics offgraphics;<br /> int pixels[];<br /> int pixscan;<br /> IntHash clut = new IntHash();<br /> boolean stopFlag;<br /> public void init() {<br /> d = getSize();<br /> int offw = (int) Math.ceil(d.width/bulbS) * bulbS;<br /> int offh = (int) Math.ceil(d.height/bulbS) * bulbS;<br /> offscreen = createImage(offw, offh);<br /> offgraphics = offscreen.getGraphics();<br /> bulbsW = offw/bulbS;<br /> bulbsH = offh/bulbS;</div> <div>THE JAVA LIBRARY<br /> Chapter 19: The Applet Class 637<br /> A good place to set the foreground and background colors is in the init( ) method.<br /> Of course, you can change these colors as often as necessary during the execution of<br /> your applet. The default foreground color is black. The default background color is<br /> light gray.<br /> You can obtain the current settings for the background and foreground colors by<br /> calling getBackground( ) and getForeground( ), respectively. They are also defined<br /> by Component and are shown here:<br /> Color getBackground( )<br /> Color getForeground( )<br /> Here is a very simple applet that sets the background color to cyan, the foreground<br /> color to red, and displays a message that illustrates the order in which the init( ),<br /> start( ), and paint( ) methods are called when an applet starts up:<br /> /* A simple applet that sets the foreground and<br /> background colors and outputs a string. */<br /> import java.awt.*;<br /> import java.applet.*;<br /> /*<br /> <applet code="Sample" width=300 height=50><br /> </applet><br /> */<br /> public class Sample extends Applet{<br /> String msg;<br /> }<br /> // set the foreground and background colors.<br /> public void init() {<br /> setBackground(Color.cyan);<br /> setForeground(Color.red);<br /> msg = "Inside init( ) --";<br /> }<br /> // Initialize the string to be displayed.<br /> public void start() {<br /> msg += " Inside start( ) --";<br /> }<br /> // Display msg in applet window.<br /> public void paint(Graphics g) {<br /> msg += " Inside paint( ).";<br /> g.drawString(msg, 10, 30);<br /> }</div> <div>THE JAVA LIBRARY<br /> Chapter 23: Images 835<br /> }<br /> }<br /> }<br /> }<br /> rs << 16 | gs << 8 | bs);<br /> Figure 23-11 shows the applet after Blur.<br /> Sharpen.java<br /> The Sharpen filter is also a subclass of Convolver and is (more or less) the inverse of<br /> Blur. It runs through every pixel in the source image array, imgpixels, and computes<br /> the average of the 3×3 box surrounding it, not counting the center. The corresponding<br /> output pixel in newimgpixels has the difference between the center pixel and the<br /> surrounding average added to it. This basically says that if a pixel is 30 brighter<br /> than its surroundings, make it another 30 brighter. If, however, it is 10 darker, then<br /> make it another 10 darker. This tends to accentuate edges while leaving smooth<br /> areas unchanged.<br /> Figure 23-11.<br /> Using the Blur filter with ImageFilterDemo</div> <div>THE JAVA LIBRARY<br /> Chapter 21: Introducing the AWT: Working with Windows, Graphics, and Text 725<br /> Method<br /> int getDescent( )<br /> Font getFont( )<br /> int getHeight( )<br /> Description<br /> Returns the descent of the font.<br /> Returns the font.<br /> Returns the height of a line of text. This value<br /> can be used to output multiple lines of text in<br /> a window.<br /> int getLeading( )<br /> Returns the space between lines of text.<br /> int getMaxAdvance( ) Returns the width of the widest character. –1<br /> is returned if this value is not available.<br /> int getMaxAscent( )<br /> Returns the maximum ascent.<br /> int getMaxDescent( )<br /> Returns the maximum descent.<br /> int[ ] getWidths( )<br /> Returns the widths of the first 256 characters.<br /> int stringWidth(String str) Returns the width of the string specified by str.<br /> String toString( )<br /> Returns the string equivalent of the<br /> invoking object.<br /> Table 21-3.<br /> Some Methods Defined by FontMetrics (continued)<br /> Displaying Multiple Lines of Text<br /> Perhaps the most common use of FontMetrics is to determine the spacing between<br /> lines of text. The second most common use is to determine the length of a string that is<br /> being displayed. Here, you will see how to accomplish these tasks.<br /> In general, to display multiple lines of text, your program must manually keep<br /> track of the current output position. Each time a newline is desired, the Y coordinate<br /> must be advanced to the beginning of the next line. Each time a string is displayed, the<br /> X coordinate must be set to the point at which the string ends. This allows the next<br /> string to be written so that it begins at the end of the preceding one.<br /> To determine the spacing between lines, you can use the value returned by<br /> getLeading( ). To determine the total height of the font, add the value returned by<br /> getAscent( ) to the value returned by getDescent( ). You can then use these values to<br /> position each line of text you output. However, in many cases, you will not need to use<br /> these individual values. Often, all that you will need to know is the total height of a<br /> line, which is the sum of the leading space and the font’s ascent and descent values.<br /> The easiest way to obtain this value is to call getHeight( ). Simply increment the Y</div> <div>662 Java™ 2: The Complete Reference<br /> InputEvent defines several integer constants that represent any modifiers, such as<br /> the control key being pressed, that might be associated with the event. Originally, the<br /> InputEvent class defined the following eight values to represent the modifiers.<br /> ALT_MASK BUTTON2_MASK META_MASK<br /> ALT_GRAPH_MASK BUTTON3_MASK SHIFT_MASK<br /> BUTTON1_MASK<br /> CTRL_MASK<br /> However, because of possible conflicts between the modifiers used by keyboard events<br /> and mouse events, and other issues, Java 2, version 1.4 added the following extended<br /> modifier values.<br /> ALT_DOWN_MASK ALT_GRAPH_DOWN_MASK BUTTON1_DOWN_MASK<br /> BUTTON2_DOWN_MASK BUTTON3_DOWN_MASK CTRL_DOWN_MASK<br /> META_DOWN_MASK SHIFT_DOWN_MASK<br /> When writing new code, it is recommended that you use the new, extended modifiers<br /> rather than the original modifiers.<br /> To test if a modifier was pressed at the time an event is generated, use the<br /> isAltDown( ), isAltGraphDown( ), isControlDown( ), isMetaDown( ), and<br /> isShiftDown( ) methods. The forms of these methods are shown here:<br /> boolean isAltDown( )<br /> boolean isAltGraphDown( )<br /> boolean isControlDown( )<br /> boolean isMetaDown( )<br /> boolean isShiftDown( )<br /> You can obtain a value that contains all of the original modifier flags by calling<br /> the getModifiers( ) method. It is shown here:<br /> int getModifiers( )<br /> You can obtain the extended modifiers by called getModifiersEx( ), which is shown here.<br /> int getModifiersEx( )<br /> This method was also added by Java 2, version 1.4.<br /> The ItemEvent Class<br /> An ItemEvent is generated when a check box or a list item is clicked or when a checkable<br /> menu item is selected or deselected. (Check boxes and list boxes are described later in this<br /> book.) There are two types of item events, which are identified by the following integer<br /> constants:</div> <div>THE JAVA LANGUAGE<br /> Chapter 4: Operators 91<br /> Operator Result<br /> < Less than<br /> >= Greater than or equal to<br /> <= Less than or equal to<br /> The outcome of these operations is a boolean value. The relational operators are<br /> most frequently used in the expressions that control the if statement and the various<br /> loop statements.<br /> Any type in Java, including integers, floating-point numbers, characters, and Booleans<br /> can be compared using the equality test, ==, and the inequality test, !=. Notice that in<br /> Java (as in C/C++/C#) equality is denoted with two equal signs, not one. (Remember:<br /> a single equal sign is the assignment operator.) Only numeric types can be compared<br /> using the ordering operators. That is, only integer, floating-point, and character operands<br /> may be compared to see which is greater or less than the other.<br /> As stated, the result produced by a relational operator is a boolean value. For<br /> example, the following code fragment is perfectly valid:<br /> int a = 4;<br /> int b = 1;<br /> boolean c = a < b;<br /> In this case, the result of a<b (which is false) is stored in c.<br /> If you are coming from a C/C++ background, please note the following. In C/C++,<br /> these types of statements are very common:<br /> int done;<br /> // ...<br /> if(!done) ... // Valid in C/C++<br /> if(done) ... // but not in Java.<br /> In Java, these statements must be written like this:<br /> if(done == 0)) ... // This is Java-style.<br /> if(done != 0) ...<br /> The reason is that Java does not define true and false in the same way as C/C++.<br /> In C/C++, true is any nonzero value and false is zero. In Java, true and false are<br /> nonnumeric values which do not relate to zero or nonzero. Therefore, to test for zero<br /> or nonzero, you must explicitly employ one or more of the relational operators.</div> <div>THE JAVA LANGUAGE<br /> Chapter 8: Inheritance 217<br /> // A Simple demonstration of abstract.<br /> abstract class A {<br /> abstract void callme();<br /> }<br /> // concrete methods are still allowed in abstract classes<br /> void callmetoo() {<br /> System.out.println("This is a concrete method.");<br /> }<br /> class B extends A {<br /> void callme() {<br /> System.out.println("B's implementation of callme.");<br /> }<br /> }<br /> class AbstractDemo {<br /> public static void main(String args[]) {<br /> B b = new B();<br /> }<br /> }<br /> b.callme();<br /> b.callmetoo();<br /> Notice that no objects of class A are declared in the program. As mentioned, it is<br /> not possible to instantiate an abstract class. One other point: class A implements a<br /> concrete method called callmetoo( ). This is perfectly acceptable. Abstract classes can<br /> include as much implementation as they see fit.<br /> Although abstract classes cannot be used to instantiate objects, they can be used<br /> to create object references, because Java’s approach to run-time polymorphism is<br /> implemented through the use of superclass references. Thus, it must be possible to<br /> create a reference to an abstract class so that it can be used to point to a subclass object.<br /> You will see this feature put to use in the next example.<br /> Using an abstract class, you can improve the Figure class shown earlier. Since<br /> there is no meaningful concept of area for an undefined two-dimensional figure, the<br /> following version of the program declares area( ) as abstract inside Figure. This, of<br /> course, means that all classes derived from Figure must override area( ).<br /> // Using abstract methods and classes.<br /> abstract class Figure {</div> <div>122 Java™ 2: The Complete Reference<br /> This program generates the following output:<br /> Pass 0: 0 1 2 3 4 5 6 7 8 9<br /> Pass 1: 0 1 2 3 4 5 6 7 8 9<br /> Pass 2: 0 1 2 3 4 5 6 7 8 9<br /> Loops complete.<br /> As you can see, the break statement in the inner loop only causes termination of that<br /> loop. The outer loop is unaffected.<br /> Here are two other points to remember about break. First, more than one break<br /> statement may appear in a loop. However, be careful. Too many break statements have<br /> the tendency to destructure your code. Second, the break that terminates a switch<br /> statement affects only that switch statement and not any enclosing loops.<br /> break was not designed to provide the normal means by which a loop is terminated. The<br /> loop’s conditional expression serves this purpose. The break statement should be used to<br /> cancel a loop only when some sort of special situation occurs.<br /> Using break as a Form of Goto<br /> In addition to its uses with the switch statement and loops, the break statement can also<br /> be employed by itself to provide a “civilized” form of the goto statement. Java does<br /> not have a goto statement, because it provides a way to branch in an arbitrary and<br /> unstructured manner. This usually makes goto-ridden code hard to understand and<br /> hard to maintain. It also prohibits certain compiler optimizations. There are, however,<br /> a few places where the goto is a valuable and legitimate construct for flow control. For<br /> example, the goto can be useful when you are exiting from a deeply nested set of loops.<br /> To handle such situations, Java defines an expanded form of the break statement. By<br /> using this form of break, you can break out of one or more blocks of code. These blocks<br /> need not be part of a loop or a switch. They can be any block. Further, you can specify<br /> precisely where execution will resume, because this form of break works with a label.<br /> As you will see, break gives you the benefits of a goto without its problems.<br /> The general form of the labeled break statement is shown here:<br /> break label;<br /> Here, label is the name of a label that identifies a block of code. When this form of break<br /> executes, control is transferred out of the named block of code. The labeled block of<br /> code must enclose the break statement, but it does not need to be the immediately<br /> enclosing block. This means that you can use a labeled break statement to exit from a<br /> set of nested blocks. But you cannot use break to transfer control to a block of code that<br /> does not enclose the break statement.</div> <div>88 Java™ 2: The Complete Reference<br /> sometimes this is undesirable. For example, if you are shifting something that does<br /> not represent a numeric value, you may not want sign extension to take place. This<br /> situation is common when you are working with pixel-based values and graphics. In<br /> these cases you will generally want to shift a zero into the high-order bit no matter<br /> what its initial value was. This is known as an unsigned shift. To accomplish this, you<br /> will use Java’s unsigned, shift-right operator, >>>, which always shifts zeros into the<br /> high-order bit.<br /> The following code fragment demonstrates the >>>. Here, a is set to –1, which sets<br /> all 32 bits to 1 in binary. This value is then shifted right 24 bits, filling the top 24 bits<br /> with zeros, ignoring normal sign extension. This sets a to 255.<br /> int a = -1;<br /> a = a >>> 24;<br /> Here is the same operation in binary form to further illustrate what is happening:<br /> 11111111 11111111 11111111 11111111 –1 in binary as an int<br /> >>>24<br /> 00000000 00000000 00000000 11111111 255 in binary as an int<br /> The >>> operator is often not as useful as you might like, since it is only meaningful<br /> for 32- and 64-bit values. Remember, smaller values are automatically promoted to int<br /> in expressions. This means that sign-extension occurs and that the shift will take place<br /> on a 32-bit rather than on an 8- or 16-bit value. That is, one might expect an unsigned<br /> right shift on a byte value to zero-fill beginning at bit 7. But this is not the case, since<br /> it is a 32-bit value that is actually being shifted. The following program demonstrates<br /> this effect:<br /> // Unsigned shifting a byte value.<br /> class ByteUShift {<br /> static public void main(String args[]) {<br /> char hex[] = {<br /> '0', '1', '2', '3', '4', '5', '6', '7',<br /> '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'<br /> };<br /> byte b = (byte) 0xf1;<br /> byte c = (byte) (b >> 4);<br /> byte d = (byte) (b >>> 4);<br /> byte e = (byte) ((b & 0xff) >> 4);</div> <div>184 Java™ 2: The Complete Reference<br /> }<br /> void test() {<br /> for(int i=0; i<10; i++) {<br /> class Inner {<br /> void display() {<br /> System.out.println("display: outer_x = " + outer_x);<br /> }<br /> }<br /> Inner inner = new Inner();<br /> inner.display();<br /> }<br /> }<br /> class InnerClassDemo {<br /> public static void main(String args[]) {<br /> Outer outer = new Outer();<br /> outer.test();<br /> }<br /> }<br /> The output from this version of the program is shown here.<br /> display: outer_x = 100<br /> display: outer_x = 100<br /> display: outer_x = 100<br /> display: outer_x = 100<br /> display: outer_x = 100<br /> display: outer_x = 100<br /> display: outer_x = 100<br /> display: outer_x = 100<br /> display: outer_x = 100<br /> display: outer_x = 100<br /> While nested classes are not used in most day-to-day programming, they are<br /> particularly helpful when handling events in an applet. We will return to the topic<br /> of nested classes in Chapter 20. There you will see how inner classes can be used to<br /> simplify the code needed to handle certain types of events. You will also learn about<br /> anonymous inner classes, which are inner classes that don't have a name.<br /> One final point: Nested classes were not allowed by the original 1.0 specification for<br /> Java. They were added by Java 1.1.</div> <div>70 Java™ 2: The Complete Reference<br /> 0 0 0 0 0<br /> 0 1 2 3 4<br /> 0 2 4 6 8<br /> 0 3 6 9 12<br /> 0 0 0 0 0<br /> 0 2 4 6 8<br /> 0 4 8 12 16<br /> 0 6 12 18 24<br /> Alternative Array Declaration Syntax<br /> There is a second form that may be used to declare an array:<br /> type[ ] var-name;<br /> Here, the square brackets follow the type specifier, and not the name of the array<br /> variable. For example, the following two declarations are equivalent:<br /> int al[] = new int[3];<br /> int[] a2 = new int[3];<br /> The following declarations are also equivalent:<br /> char twod1[][] = new char[3][4];<br /> char[][] twod2 = new char[3][4];<br /> This alternative declaration form is included as a convenience, and is also useful when<br /> specifying an array as a return type for a method.<br /> A Few Words About Strings<br /> As you may have noticed, in the preceding discussion of data types and arrays there<br /> has been no mention of strings or a string data type. This is not because Java does not<br /> support such a type—it does. It is just that Java’s string type, called String, isnota<br /> simple type. Nor is it simply an array of characters (as are strings in C/C++). Rather,<br /> String defines an object, and a full description of it requires an understanding of several<br /> object-related features. As such, it will be covered later in this book, after objects are<br /> described. However, so that you can use simple strings in example programs, the<br /> following brief introduction is in order.<br /> The String type is used to declare string variables. You can also declare arrays of<br /> strings. A quoted string constant can be assigned to a String variable. A variable</div> <div>556 Java™ 2: The Complete Reference<br /> Buffering an input stream also provides the foundation required to support moving<br /> backward in the stream of the available buffer. Beyond the read( ) and skip( ) methods<br /> implemented in any InputStream, BufferedInputStream also supports the mark( ) and<br /> reset( ) methods. This support is reflected by BufferedInputStream.markSupported( )<br /> returning true.<br /> The following example contrives a situation where we can use mark( ) to remember<br /> where we are in an input stream and later use reset( ) to get back there. This example is<br /> parsing a stream for the HTML entity reference for the copyright symbol. Such a<br /> reference begins with an ampersand (&) and ends with a semicolon (;) without any<br /> intervening whitespace. The sample input has two ampersands to show the case where<br /> the reset( ) happens and where it does not.<br /> // Use buffered input.<br /> import java.io.*;<br /> class BufferedInputStreamDemo {<br /> public static void main(String args[]) throws IOException {<br /> String s = "This is a © copyright symbol " +<br /> "but this is © not.\n";<br /> byte buf[] = s.getBytes();<br /> ByteArrayInputStream in = new ByteArrayInputStream(buf);<br /> BufferedInputStream f = new BufferedInputStream(in);<br /> int c;<br /> boolean marked = false;<br /> while ((c = f.read()) != -1) {<br /> switch(c) {<br /> case '&':<br /> if (!marked) {<br /> f.mark(32);<br /> marked = true;<br /> } else {<br /> marked = false;<br /> }<br /> break;<br /> case ';':<br /> if (marked) {<br /> marked = false;<br /> System.out.print("(c)");<br /> } else<br /> System.out.print((char) c);<br /> break;</div> <div>THE JAVA LANGUAGE<br /> Chapter 5: Control Statements 103<br /> statement;<br /> else if(condition)<br /> statement;<br /> .<br /> .<br /> .<br /> else<br /> statement;<br /> The if statements are executed from the top down. As soon as one of the conditions<br /> controlling the if is true, the statement associated with that if is executed, and the rest<br /> of the ladder is bypassed. If none of the conditions is true, then the final else statement<br /> will be executed. The final else acts as a default condition; that is, if all other conditional<br /> tests fail, then the last else statement is performed. If there is no final else and all other<br /> conditions are false, then no action will take place.<br /> Here is a program that uses an if-else-if ladder to determine which season a particular<br /> month is in.<br /> // Demonstrate if-else-if statements.<br /> class IfElse {<br /> public static void main(String args[]) {<br /> int month = 4; // April<br /> String season;<br /> if(month == 12 || month == 1 || month == 2)<br /> season = "Winter";<br /> else if(month == 3 || month == 4 || month == 5)<br /> season = "Spring";<br /> else if(month == 6 || month == 7 || month == 8)<br /> season = "Summer";<br /> else if(month == 9 || month == 10 || month == 11)<br /> season = "Autumn";<br /> else<br /> season = "Bogus Month";<br /> }<br /> }<br /> System.out.println("April is in the " + season + ".");<br /> Here is the output produced by the program:<br /> April is in the Spring.</div> <div>352 Java™ 2: The Complete Reference<br /> String Concatenation<br /> In general, Java does not allow operators to be applied to String objects. The one<br /> exception to this rule is the + operator, which concatenates two strings, producing a<br /> String object as the result. This allows you to chain together a series of + operations.<br /> For example, the following fragment concatenates three strings:<br /> String age = "9";<br /> String s = "He is " + age + " years old.";<br /> System.out.println(s);<br /> This displays the string “He is 9 years old.”<br /> One practical use of string concatenation is found when you are creating very long<br /> strings. Instead of letting long strings wrap around within your source code, you can<br /> break them into smaller pieces, using the + to concatenate them. Here is an example:<br /> // Using concatenation to prevent long lines.<br /> class ConCat {<br /> public static void main(String args[]) {<br /> String longStr = "This could have been " +<br /> "a very long line that would have " +<br /> "wrapped around. But string concatenation " +<br /> "prevents this.";<br /> }<br /> }<br /> System.out.println(longStr);<br /> String Concatenation with Other Data Types<br /> You can concatenate strings with other types of data. For example, consider this<br /> slightly different version of the earlier example:<br /> int age = 9;<br /> String s = "He is " + age + " years old.";<br /> System.out.println(s);<br /> In this case, age is an int rather than another String, but the output produced is the<br /> same as before. This is because the int value in age is automatically converted into its<br /> string representation within a String object. This string is then concatenated as before.<br /> The compiler will convert an operand to its string equivalent whenever the other<br /> operand of the + is an instance of String.</div> <div>960 Java™ 2: The Complete Reference<br /> The GenericServlet Class<br /> The GenericServlet class provides implementations of the basic life cycle methods for<br /> a servlet and is typically subclassed by servlet developers. GenericServlet implements<br /> the Servlet and ServletConfig interfaces. In addition, a method to append a string to<br /> the server log file is available. The signatures of this method are shown here:<br /> void log(String s)<br /> void log(String s, Throwable e)<br /> Here, s is the string to be appended to the log, and e is an exception that occurred.<br /> The ServletInputStream Class<br /> The ServletInputStream class extends InputStream. It is implemented by the server<br /> and provides an input stream that a servlet developer can use to read the data from a<br /> client request. It defines the default constructor. In addition, a method is provided to<br /> read bytes from the stream. Its signature is shown here:<br /> int readLine(byte[ ] buffer, int offset, int size) throws IOException<br /> Here, buffer is the array into which size bytes are placed starting at offset. The method<br /> returns the actual number of bytes read or –1 if an end-of-stream condition is encountered.<br /> The ServletOutputStream Class<br /> The ServletOutputStream class extends OutputStream. It is implemented by the<br /> server and provides an output stream that a servlet developer can use to write data<br /> to a client response. A default constructor is defined. It also defines the print( ) and<br /> println( ) methods, which output data to the stream.<br /> The Servlet Exception Classes<br /> javax.servlet defines two exceptions. The first is ServletException, which indicates that<br /> a servlet problem has occurred. The second is UnavailableException, which extends<br /> ServletException. It indicates that a servlet is unavailable.<br /> Reading Servlet Parameters<br /> The ServletRequest class includes methods that allow you to read the names and<br /> values of parameters that are included in a client request. We will develop a servlet<br /> that illustrates their use. The example contains two files. A Web page is defined in<br /> PostParameters.htm and a servlet is defined in PostParametersServlet.java.<br /> The HTML source code for PostParameters.htm is shown in the following listing. It<br /> defines a table that contains two labels and two text fields. One of the labels is Employee</div> <div>THE JAVA LANGUAGE<br /> Chapter 1: The Genesis of Java 5<br /> Prior to C, programmers usually had to choose between languages that optimized<br /> one set of traits or the other. For example, although FORTRAN could be used to write<br /> fairly efficient programs for scientific applications, it was not very good for systems<br /> code. And while BASIC was easy to learn, it wasn’t very powerful, and its lack of<br /> structure made its usefulness questionable for large programs. Assembly language<br /> can be used to produce highly efficient programs, but it is not easy to learn or use<br /> effectively. Further, debugging assembly code can be quite difficult.<br /> Another compounding problem was that early computer languages such as BASIC,<br /> COBOL, and FORTRAN were not designed around structured principles. Instead, they<br /> relied upon the GOTO as a primary means of program control. As a result, programs<br /> written using these languages tended to produce “spaghetti code”—a mass of tangled<br /> jumps and conditional branches that make a program virtually impossible to<br /> understand. While languages like Pascal are structured, they were not designed for<br /> efficiency, and failed to include certain features necessary to make them applicable to<br /> a wide range of programs. (Specifically, given the standard dialects of Pascal available<br /> at the time, it was not practical to consider using Pascal for systems-level code.)<br /> So, just prior to the invention of C, no one language had reconciled the conflicting<br /> attributes that had dogged earlier efforts. Yet the need for such a language was<br /> pressing. By the early 1970s, the computer revolution was beginning to take hold, and<br /> the demand for software was rapidly outpacing programmers’ ability to produce it.<br /> A great deal of effort was being expended in academic circles in an attempt to create a<br /> better computer language. But, and perhaps most importantly, a secondary force was<br /> beginning to be felt. Computer hardware was finally becoming common enough that a<br /> critical mass was being reached. No longer were computers kept behind locked doors.<br /> For the first time, programmers were gaining virtually unlimited access to their<br /> machines. This allowed the freedom to experiment. It also allowed programmers to<br /> begin to create their own tools. On the eve of C’s creation, the stage was set for a<br /> quantum leap forward in computer languages.<br /> Invented and first implemented by Dennis Ritchie on a DEC PDP-11 running the<br /> UNIX operating system, C was the result of a development process that started with<br /> an older language called BCPL, developed by Martin Richards. BCPL influenced a<br /> language called B, invented by Ken Thompson, which led to the development of C<br /> in the 1970s. For many years, the de facto standard for C was the one supplied with<br /> the UNIX operating system and described in The C Programming Language by Brian<br /> Kernighan and Dennis Ritchie (Prentice-Hall, 1978). C was formally standardized in<br /> December 1989, when the American National Standards Institute (ANSI) standard for<br /> C was adopted.<br /> The creation of C is considered by many to have marked the beginning of the<br /> modern age of computer languages. It successfully synthesized the conflicting<br /> attributes that had so troubled earlier languages. The result was a powerful, efficient,<br /> structured language that was relatively easy to learn. It also included one other, nearly<br /> intangible aspect: it was a programmer’s language. Prior to the invention of C, computer<br /> languages were generally designed either as academic exercises or by bureaucratic<br /> committees. C is different. It was designed, implemented, and developed by real,</div> <div>THE JAVA LIBRARY<br /> Chapter 14: Exploring java.lang 401<br /> Java 2, version 1.4 adds a method called getDirectionality( ) which can be used to<br /> determine the direction of a character. Several new constants have been added which<br /> describe directionality. Most programs will not need to use character directionality.<br /> Character also defines the equals( ) and hashCode( ) methods.<br /> Two other character-related classes are Character.Subset, used to describe a subset<br /> of Unicode, and Character.UnicodeBlock, which contains Unicode character blocks.<br /> Boolean<br /> Boolean is a very thin wrapper around boolean values, which is useful mostly when<br /> you want to pass a boolean variable by reference. It contains the constants TRUE and<br /> FALSE, which define true and false Boolean objects. Boolean also defines the TYPE<br /> field, which is the Class object for boolean. Boolean defines these constructors:<br /> Boolean(boolean boolValue)<br /> Boolean(String boolString)<br /> In the first version, boolValue must be either true or false. In the second version, if<br /> boolString contains the string “true” (in uppercase or lowercase), then the new Boolean<br /> object will be true. Otherwise, it will be false.<br /> Boolean defines the methods shown in Table 14-8.<br /> Method<br /> boolean booleanValue( )<br /> boolean equals(Object boolObj)<br /> static boolean<br /> getBoolean(String propertyName)<br /> int hashCode( )<br /> String toString( )<br /> static String toString(boolean boolVal)<br /> static Boolean valueOf(boolean boolVal)<br /> static Boolean valueOf(String boolString)<br /> Description<br /> Returns boolean equivalent.<br /> Returns true if the invoking object is equivalent<br /> to boolObj. Otherwise, it returns false.<br /> Returns true if the system property specified<br /> by propertyName is true. Otherwise, it returns<br /> false.<br /> Returns the hash code for the invoking object.<br /> Returns the string equivalent of the invoking<br /> object.<br /> Returns the string equivalent of boolVal.<br /> (Added by Java 2, version 1.4)<br /> Returns the Boolean equivalent of boolVal.<br /> (Added by Java 2, version 1.4)<br /> Returns true if boolString contains the string<br /> “true” (in uppercase or lowercase).<br /> Otherwise, it returns false.<br /> Table 14-8.<br /> The Methods Defined by Boolean</div> <div>922 Java™ 2: The Complete Reference<br /> In Part II, you saw how to build user interfaces with the AWT classes. Here, we will<br /> take a tour of a supercharged alternative called Swing. Swing is a set of classes that<br /> provides more powerful and flexible components than are possible with the AWT.<br /> In addition to the familiar components, such as buttons, check boxes, and labels, Swing<br /> supplies several exciting additions, including tabbed panes, scroll panes, trees, and<br /> tables. Even familiar components such as buttons have more capabilities in Swing. For<br /> example, a button may have both an image and a text string associated with it. Also,<br /> the image can be changed as the state of the button changes.<br /> Unlike AWT components, Swing components are not implemented by<br /> platform-specific code. Instead, they are written entirely in Java and, therefore, are<br /> platform-independent. The term lightweight is used to describe such elements.<br /> The number of classes and interfaces in the Swing packages is substantial, and this<br /> chapter provides an overview of just a few. Swing is an area that you will want to<br /> explore further on your own.<br /> The Swing component classes that are used in this book are shown here:<br /> Class<br /> AbstractButton<br /> ButtonGroup<br /> ImageIcon<br /> JApplet<br /> JButton<br /> JCheckBox<br /> JComboBox<br /> JLabel<br /> JRadioButton<br /> JScrollPane<br /> JTabbedPane<br /> JTable<br /> JTextField<br /> JTree<br /> Description<br /> Abstract superclass for Swing buttons.<br /> Encapsulates a mutually exclusive set of buttons.<br /> Encapsulates an icon.<br /> The Swing version of Applet.<br /> The Swing push button class.<br /> The Swing check box class.<br /> Encapsulates a combo box (an combination of a<br /> drop-down list and text field).<br /> The Swing version of a label.<br /> The Swing version of a radio button.<br /> Encapsulates a scrollable window.<br /> Encapsulates a tabbed window.<br /> Encapsulates a table-based control.<br /> The Swing version of a text field.<br /> Encapsulates a tree-based control.</div> <div>THE JAVA LANGUAGE<br /> Chapter 12: I/O, Applets, and Other Topics 315<br /> Byte Streams and Character Streams<br /> Java 2 defines two types of streams: byte and character. Byte streams provide a<br /> convenient means for handling input and output of bytes. Byte streams are used, for<br /> example, when reading or writing binary data. Character streams provide a convenient<br /> means for handling input and output of characters. They use Unicode and, therefore,<br /> can be internationalized. Also, in some cases, character streams are more efficient than<br /> byte streams.<br /> The original version of Java (Java 1.0) did not include character streams and, thus,<br /> all I/O was byte-oriented. Character streams were added by Java 1.1, and certain<br /> byte-oriented classes and methods were deprecated. This is why older code that<br /> doesn’t use character streams should be updated to take advantage of them, where<br /> appropriate.<br /> One other point: at the lowest level, all I/O is still byte-oriented. The<br /> character-based streams simply provide a convenient and efficient means for handling<br /> characters.<br /> An overview of both byte-oriented streams and character-oriented streams is<br /> presented in the following sections.<br /> The Byte Stream Classes<br /> Byte streams are defined by using two class hierarchies. At the top are two abstract<br /> classes: InputStream and OutputStream. Each of these abstract classes has several<br /> concrete subclasses, that handle the differences between various devices, such as disk<br /> files, network connections, and even memory buffers. The byte stream classes are<br /> shown in Table 12-1. A few of these classes are discussed later in this section. Others<br /> are described in Part II. Remember, to use the stream classes, you must import java.io.<br /> The abstract classes InputStream and OutputStream define several key methods<br /> that the other stream classes implement. Two of the most important are read( ) and<br /> write( ), which, respectively, read and write bytes of data. Both methods are declared<br /> as abstract inside InputStream and OutputStream. They are overridden by derived<br /> stream classes.<br /> The Character Stream Classes<br /> Character streams are defined by using two class hierarchies. At the top are two<br /> abstract classes, Reader and Writer. These abstract classes handle Unicode character<br /> streams. Java has several concrete subclasses of each of these. The character stream<br /> classes are shown in Table 12-2.<br /> The abstract classes Reader and Writer define several key methods that the other<br /> stream classes implement. Two of the most important methods are read( ) and write( ),<br /> which read and write characters of data, respectively. These methods are overridden<br /> by derived stream classes.</div> <div>THE JAVA LIBRARY<br /> Chapter 22: Using AWT Controls, Layout Managers, and Menus 771<br /> Here is a sample program that creates a 4×4 grid and fills it in with 15 buttons, each<br /> labeled with its index:<br /> // Demonstrate GridLayout<br /> import java.awt.*;<br /> import java.applet.*;<br /> /*<br /> <applet code="GridLayoutDemo" width=300 height=200><br /> </applet><br /> */<br /> public class GridLayoutDemo extends Applet {<br /> static final int n = 4;<br /> public void init() {<br /> setLayout(new GridLayout(n, n));<br /> setFont(new Font("SansSerif", Font.BOLD, 24));<br /> }<br /> }<br /> for(int i = 0; i < n; i++) {<br /> for(int j = 0; j < n; j++) {<br /> int k = i * n + j;<br /> if(k > 0)<br /> add(new Button("" + k));<br /> }<br /> }<br /> Following is the output generated by the GridLayoutDemo applet:</div> <div>572 Java™ 2: The Complete Reference<br /> }<br /> }<br /> while ((c = f.read()) != -1) {<br /> switch(c) {<br /> case '=':<br /> if ((c = f.read()) == '=')<br /> System.out.print(".eq.");<br /> else {<br /> System.out.print("<-");<br /> f.unread(c);<br /> }<br /> break;<br /> default:<br /> System.out.print((char) c);<br /> break;<br /> }<br /> }<br /> PrintWriter<br /> PrintWriter is essentially a character-oriented version of PrintStream. It provides the<br /> formatted output methods print( ) and println( ). PrintWriter has four constructors:<br /> PrintWriter(OutputStream outputStream)<br /> PrintWriter(OutputStream outputStream, boolean flushOnNewline)<br /> PrintWriter(Writer outputStream)<br /> PrintWriter(Writer outputStream, boolean flushOnNewline)<br /> where flushOnNewline controls whether Java flushes the output stream every time<br /> println( ) is called. If flushOnNewline is true, flushing automatically takes place. If false,<br /> flushing is not automatic. The first and third constructors do not automatically flush.<br /> Java’s PrintWriter objects support the print( ) and println( ) methods for all types,<br /> including Object. If an argument is not a simple type, the PrintWriter methods will call<br /> the object’s toString( ) method and then print out the result.<br /> Using Stream I/O<br /> The following example demonstrates several of Java’s I/O character stream classes and<br /> methods. This program implements the standard wc (word count) command. The<br /> program has two modes: if no filenames are provided as arguments, the program</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 28: Migrating from C++ to Java 1001<br /> Converting C++ Multiple-Inheritance<br /> Hierarchies<br /> C++ allows one class to inherit two or more base classes at the same time. Java does<br /> not. To understand the difference, consider the two hierarchies depicted here:<br /> In both cases, subclass C inherits classes A and B. However, in the hierarchy on the left,<br /> C inherits both A and B at the same time. In the one on the right, B inherits A, and C<br /> inherits B. By not allowing the inheritance of multiple base classes by a single subclass,<br /> Java greatly simplifies the inheritance model. Multiple inheritance carries with it<br /> several special cases that must be handled. This adds overhead to both the compiler<br /> and the run-time system, while providing only marginal benefit for the programmer.<br /> Since C++ supports multiple inheritance and Java does not, you may have to deal<br /> with this issue when porting C++ applications to Java. While every situation is<br /> different, two general pieces of advice can be offered. First, in many cases, multiple<br /> inheritance is employed in a C++ program when there is actually no need to do so.<br /> When this is the case, just convert the class structure to a single-inheritance hierarchy.<br /> For example, consider this C++ class hierarchy that defines a class called House:<br /> class Foundation {<br /> // ...<br /> };<br /> class Walls {<br /> // ...<br /> };<br /> class Rooms {<br /> // ...<br /> };<br /> class House : public Foundation, Walls, Rooms {<br /> // ...<br /> };</div> <div>THE JAVA LANGUAGE<br /> Chapter 12: I/O, Applets, and Other Topics 331<br /> }<br /> }<br /> g.drawString("A Simple Applet", 20, 20);<br /> In general, you can quickly iterate through applet development by using these<br /> three steps:<br /> 1. Edit a Java source file.<br /> 2. Compile your program.<br /> 3. Execute the applet viewer, specifying the name of your applet’s source file. The<br /> applet viewer will encounter the APPLET tag within the comment and execute<br /> your applet.<br /> The window produced by SimpleApplet, as displayed by the applet viewer, is<br /> shown in the following illustration:<br /> While the subject of applets is more fully discussed later in this book, here are the<br /> key points that you should remember now:<br /> ■ Applets do not need a main( ) method.<br /> ■ Applets must be run under an applet viewer or a Java-compatible browser.<br /> ■ User I/O is not accomplished with Java’s stream I/O classes. Instead, applets<br /> use the interface provided by the AWT.<br /> The transient and volatile Modifiers<br /> Java defines two interesting type modifiers: transient and volatile. These modifiers are<br /> used to handle somewhat specialized situations.<br /> When an instance variable is declared as transient, then its value need not persist<br /> when an object is stored. For example:<br /> class T {<br /> transient int a; // will not persist</div> <div>THE JAVA LANGUAGE<br /> Chapter 4: Operators 81<br /> Operator<br /> Result<br /> ^= Bitwise exclusive OR assignment<br /> >>= Shift right assignment<br /> >>>= Shift right zero fill assignment<br /> <<= Shift left assignment<br /> Since the bitwise operators manipulate the bits within an integer, it is important to<br /> understand what effects such manipulations may have on a value. Specifically, it is<br /> useful to know how Java stores integer values and how it represents negative numbers.<br /> So, before continuing, let’s briefly review these two topics.<br /> All of the integer types are represented by binary numbers of varying bit widths.<br /> For example, the byte value for 42 in binary is 00101010, where each position represents<br /> a power of two, starting with 2 0 at the rightmost bit. The next bit position to the left<br /> would be 2 1 , or 2, continuing toward the left with 2 2 , or 4, then 8, 16, 32, and so on. So<br /> 42 has 1 bits set at positions 1, 3, and 5 (counting from 0 at the right); thus 42 is the sum<br /> of 2 1 + 2 3 + 2 5 , which is 2 + 8 + 32.<br /> All of the integer types (except char) are signed integers. This means that they can<br /> represent negative values as well as positive ones. Java uses an encoding known as<br /> two’s complement, which means that negative numbers are represented by inverting<br /> (changing 1’s to 0’s and vice versa) all of the bits in a value, then adding 1 to the result.<br /> For example, –42 is represented by inverting all of the bits in 42, or 00101010, which<br /> yields 11010101, then adding 1, which results in 11010110, or –42. To decode a negative<br /> number, first invert all of the bits, then add 1. –42, or 11010110 inverted yields 00101001,<br /> or 41, so when you add 1 you get 42.<br /> The reason Java (and most other computer languages) uses two’s complement is easy<br /> to see when you consider the issue of zero crossing. Assuming a byte value, zero is<br /> represented by 00000000. In one’s complement, simply inverting all of the bits creates<br /> 11111111, which creates negative zero. The trouble is that negative zero is invalid in<br /> integer math. This problem is solved by using two’s complement to represent negative<br /> values. When using two’s complement, 1 is added to the complement, producing<br /> 100000000. This producesa1bit too far to the left to fit back into the byte value, resulting<br /> in the desired behavior, where –0 is the same as 0, and 11111111 is the encoding for –1.<br /> Although we used a byte value in the preceding example, the same basic principle<br /> applies to all of Java’s integer types.<br /> Because Java uses two’s complement to store negative numbers—and because all<br /> integers are signed values in Java—applying the bitwise operators can easily produce<br /> unexpected results. For example, turning on the high-order bit will cause the resulting<br /> value to be interpreted as a negative number, whether this is what you intended or not.<br /> To avoid unpleasant surprises, just remember that the high-order bit determines the<br /> sign of an integer no matter how that high-order bit gets set.</div> <div>418 Java™ 2: The Complete Reference<br /> The methods defined by Class are often useful in situations where run-time type<br /> information about an object is required. As Table 14-13 shows, methods are provided<br /> that allow you to determine additional information about a particular class, such as its<br /> public constructors, fields, and methods. This is important for the Java Beans<br /> functionality, which is discussed later in this book.<br /> The following program demonstrates getClass( ) (inherited from Object) and<br /> getSuperclass( ) (from Class):<br /> // Demonstrate Run-Time Type Information.<br /> class X {<br /> int a;<br /> float b;<br /> }<br /> class Y extends X {<br /> double c;<br /> }<br /> class RTTI {<br /> public static void main(String args[]) {<br /> X x = new X();<br /> Y y = new Y();<br /> Class clObj;<br /> clObj = x.getClass(); // get Class reference<br /> System.out.println("x is object of type: " +<br /> clObj.getName());<br /> }<br /> }<br /> clObj = y.getClass(); // get Class reference<br /> System.out.println("y is object of type: " +<br /> clObj.getName());<br /> clObj = clObj.getSuperclass();<br /> System.out.println("y's superclass is " +<br /> clObj.getName());<br /> The output from this program is shown here:</div> <div>462 Java™ 2: The Complete Reference<br /> The output from the program is shown here:<br /> J.W. West<br /> 11 Oak Ave<br /> Urbana IL 61801<br /> Ralph Baker<br /> 1142 Maple Lane<br /> Mahomet IL 61853<br /> Tom Carlton<br /> 867 Elm St<br /> Champaign IL 61820<br /> Aside from storing a user-defined class in a collection, another important thing to<br /> notice about the preceding program is that it is quite short. When you consider that it<br /> sets up a linked list that can store, retrieve, and process mailing addresses in about 50<br /> lines of code, the power of the collections framework begins to become apparent. As<br /> most readers know, if all of this functionality had to be coded manually, the program<br /> would be several times longer. Collections offer off-the-shelf solutions to a wide variety<br /> of programming problems. You should use them whenever the situation presents itself.<br /> The RandomAccess Interface<br /> Java 2, version 1.4 adds the RandomAccess interface. This interface contains no members.<br /> However, by implementing this interface, a collection signals that it supports efficient<br /> random access to its elements. Although a collection might support random access, it<br /> might not do so efficiently. By checking for the RandomAccess interface, client code<br /> can determine at run time whether a collection is suitable for certain types of random<br /> access operations—especially as they apply to large collections. (You can use instanceof<br /> to determine if a class implements an interface.) RandomAccess is implemented by<br /> ArrayList and by the legacy Vector class.<br /> Working with Maps<br /> A map is an object that stores associations between keys and values, or key/value pairs.<br /> Given a key, you can find its value. Both keys and values are objects. The keys must be<br /> unique, but the values may be duplicated. Some maps can accept a null key and null<br /> values, others cannot.<br /> The Map Interfaces<br /> Because the map interfaces define the character and nature of maps, this discussion of<br /> maps begins with them. The following interfaces support maps:</div> <div>216 Java™ 2: The Complete Reference<br /> types of objects. In this case, if an object is derived from Figure, then its area can be<br /> obtained by calling area( ). The interface to this operation is the same no matter what<br /> type of figure is being used.<br /> Using Abstract Classes<br /> There are situations in which you will want to define a superclass that declares the<br /> structure of a given abstraction without providing a complete implementation of every<br /> method. That is, sometimes you will want to create a superclass that only defines a<br /> generalized form that will be shared by all of its subclasses, leaving it to each subclass<br /> to fill in the details. Such a class determines the nature of the methods that the<br /> subclasses must implement. One way this situation can occur is when a superclass<br /> is unable to create a meaningful implementation for a method. This is the case with<br /> the class Figure used in the preceding example. The definition of area( ) is simply a<br /> placeholder. It will not compute and display the area of any type of object.<br /> As you will see as you create your own class libraries, it is not uncommon for a<br /> method to have no meaningful definition in the context of its superclass. You can<br /> handle this situation two ways. One way, as shown in the previous example, is to<br /> simply have it report a warning message. While this approach can be useful in certain<br /> situations—such as debugging—it is not usually appropriate. You may have methods<br /> which must be overridden by the subclass in order for the subclass to have any meaning.<br /> Consider the class Triangle. It has no meaning if area( ) is not defined. In this case, you<br /> want some way to ensure that a subclass does, indeed, override all necessary methods.<br /> Java’s solution to this problem is the abstract method.<br /> You can require that certain methods be overridden by subclasses by specifying<br /> the abstract type modifier. These methods are sometimes referred to as subclasser<br /> responsibility because they have no implementation specified in the superclass. Thus,<br /> a subclass must override them—it cannot simply use the version defined in the<br /> superclass. To declare an abstract method, use this general form:<br /> abstract type name(parameter-list);<br /> As you can see, no method body is present.<br /> Any class that contains one or more abstract methods must also be declared<br /> abstract. To declare a class abstract, you simply use the abstract keyword in front of the<br /> class keyword at the beginning of the class declaration. There can be no objects of an<br /> abstract class. That is, an abstract class cannot be directly instantiated with the new<br /> operator. Such objects would be useless, because an abstract class is not fully defined.<br /> Also, you cannot declare abstract constructors, or abstract static methods. Any subclass<br /> of an abstract class must either implement all of the abstract methods in the superclass,<br /> or be itself declared abstract.<br /> Here is a simple example of a class with an abstract method, followed by a class<br /> which implements that method:</div> <div>636 Java™ 2: The Complete Reference<br /> Simple Applet Display Methods<br /> As we’ve mentioned, applets are displayed in a window and they use the AWT to<br /> perform input and output. Although we will examine the methods, procedures, and<br /> techniques necessary to fully handle the AWT windowed environment in subsequent<br /> chapters, a few are described here, because we will use them to write sample applets.<br /> As we described in Chapter 12, to output a string to an applet, use drawString( ),<br /> which is a member of the Graphics class. Typically, it is called from within either<br /> update( ) or paint( ). It has the following general form:<br /> void drawString(String message, int x, int y)<br /> Here, message is the string to be output beginning at x,y. In a Java window, the<br /> upper-left corner is location 0,0. The drawString( ) method will not recognize newline<br /> characters. If you want to start a line of text on another line, you must do so manually,<br /> specifying the precise X,Y location where you want the line to begin. (As you will see in<br /> later chapters, there are techniques that make this process easy.)<br /> To set the background color of an applet’s window, use setBackground( ).Toset the<br /> foreground color (the color in which text is shown, for example), use setForeground( ).<br /> These methods are defined by Component, and they have the following general forms:<br /> void setBackground(Color newColor)<br /> void setForeground(Color newColor)<br /> Here, newColor specifies the new color. The class Color defines the constants shown<br /> here that can be used to specify colors:<br /> Color.black<br /> Color.blue<br /> Color.cyan<br /> Color.darkGray<br /> Color.gray<br /> Color.green<br /> Color.lightGray<br /> Color.magenta<br /> Color.orange<br /> Color.pink<br /> Color.red<br /> Color.white<br /> Color.yellow<br /> For example, this sets the background color to green and the text color to red:<br /> setBackground(Color.green);<br /> setForeground(Color.red);</div> <div>THE JAVA LIBRARY<br /> Chapter 23: Images 829<br /> }<br /> return a.createImage(new FilteredImageSource(in.getSource(), this));<br /> }<br /> public int filterRGB(int x, int y, int rgb) {<br /> int r = (rgb >> 16) & 0xff;<br /> int g = (rgb >> 8) & 0xff;<br /> int b = rgb & 0xff;<br /> int k = (int) (.56 * g + .33 * r + .11 * b);<br /> return (0xff000000 | k << 16 | k << 8 | k);<br /> }<br /> Invert.java<br /> The Invert filter is also quite simple. It takes apart the red, green, and blue channels<br /> and then inverts them by subtracting them from 255. These inverted values are packed<br /> back into a pixel value and returned.<br /> import java.applet.*;<br /> import java.awt.*;<br /> import java.awt.image.*;<br /> class Invert extends RGBImageFilter implements PlugInFilter {<br /> public Image filter(Applet a, Image in) {<br /> return a.createImage(new FilteredImageSource(in.getSource(), this));<br /> }<br /> public int filterRGB(int x, int y, int rgb) {<br /> int r = 0xff - (rgb >> 16) & 0xff;<br /> int g = 0xff - (rgb >> 8) & 0xff;<br /> int b = 0xff - rgb & 0xff;<br /> return (0xff000000 | r << 16 | g << 8 | b);<br /> }<br /> }<br /> Figure 23-9 shows the image after it has been run through the Invert filter.<br /> Contrast.java<br /> The Contrast filter is very similar to Grayscale, except its override of filterRGB( ) is<br /> slightly more complicated. The algorithm it uses for contrast enhancement takes the<br /> red, green, and blue values separately and boosts them by 1.2 times if they are already<br /> brighter than 128. If they are below 128, then they are divided by 1.2. The boosted<br /> values are properly clamped at 255 by the multclamp( ) method.</div> <div>152 Java™ 2: The Complete Reference<br /> or how the data is actually managed within the class. In a sense, a class is like a “data<br /> engine.” No knowledge of what goes on inside the engine is required to use the engine<br /> through its controls. In fact, since the details are hidden, its inner workings can be<br /> changed as needed. As long as your code uses the class through its methods, internal<br /> details can change without causing side effects outside the class.<br /> To see a practical application of the preceding discussion, let’s develop one of the<br /> archetypal examples of encapsulation: the stack. A stack stores data using first-in, last-out<br /> ordering. That is, a stack is like a stack of plates on a table—the first plate put down<br /> on the table is the last plate to be used. Stacks are controlled through two operations<br /> traditionally called push and pop. To put an item on top of the stack, you will use push.<br /> To take an item off the stack, you will use pop. As you will see, it is easy to encapsulate<br /> the entire stack mechanism.<br /> Here is a class called Stack that implements a stack for integers:<br /> // This class defines an integer stack that can hold 10 values.<br /> class Stack {<br /> int stck[] = new int[10];<br /> int tos;<br /> }<br /> // Initialize top-of-stack<br /> Stack() {<br /> tos = -1;<br /> }<br /> // Push an item onto the stack<br /> void push(int item) {<br /> if(tos==9)<br /> System.out.println("Stack is full.");<br /> else<br /> stck[++tos] = item;<br /> }<br /> // Pop an item from the stack<br /> int pop() {<br /> if(tos < 0) {<br /> System.out.println("Stack underflow.");<br /> return 0;<br /> }<br /> else<br /> return stck[tos--];<br /> }</div> <div>THE JAVA LIBRARY<br /> Chapter 15: java.util Part 1: The Collections Framework 497<br /> }<br /> }<br /> // Deposit 1,000 into John Doe's account<br /> bal = ((Double)balance.get("John Doe")).doubleValue();<br /> balance.put("John Doe", new Double(bal+1000));<br /> System.out.println("John Doe's new balance: " +<br /> balance.get("John Doe"));<br /> The output from this program is shown here:<br /> Todd Hall: 99.22<br /> Ralph Smith: -19.08<br /> John Doe: 3434.34<br /> Jane Baker: 1378.0<br /> Tom Smith: 123.22<br /> John Doe’s new balance: 4434.34<br /> One important point: like the map classes, Hashtable does not directly support<br /> iterators. Thus, the preceding program uses an enumeration to display the contents<br /> of balance. However, you can obtain set-views of the hash table, which permits the<br /> use of iterators. To do so, you simply use one of the collection-view methods defined<br /> by Map, such as entrySet( ) or keySet( ). For example, you can obtain a set-view of the<br /> keys and iterate through them. Here is a reworked version of the program that shows<br /> this technique:<br /> // Use iterators with a Hashtable.<br /> import java.util.*;<br /> class HTDemo2 {<br /> public static void main(String args[]) {<br /> Hashtable balance = new Hashtable();<br /> String str;<br /> double bal;<br /> balance.put("John Doe", new Double(3434.34));<br /> balance.put("Tom Smith", new Double(123.22));<br /> balance.put("Jane Baker", new Double(1378.00));<br /> balance.put("Todd Hall", new Double(99.22));<br /> balance.put("Ralph Smith", new Double(-19.08));<br /> // show all balances in hashtable</div> <div>1028 Java™ 2: The Complete Reference<br /> }<br /> }<br /> try { Thread.sleep(100); } catch (InterruptedException e) {}<br /> createCellFromWorkPixels(c);<br /> column_width += WIDTH_INCREMENT;<br /> }<br /> work_pixels = null;<br /> void NextCell() {<br /> int old_column_width = MAX_COLUMN_WIDTH - column_width;<br /> for(int p = pixels_per_cell - cell_w; p >= 0; p -= cell_w) {<br /> for (int x = 0; x < rightmost_columns_x_start; x +=<br /> MAX_COLUMN_WIDTH) {<br /> System.arraycopy(next_pixels, x + p, work_pixels,<br /> old_column_width + x + p, column_width);<br /> }<br /> if(old_column_width <= rightmost_columns_max_width) {<br /> System.arraycopy(next_pixels, rightmost_columns_x_start + p,<br /> work_pixels, rightmost_columns_x_start +<br /> old_column_width + p - 1,<br /> rightmost_columns_max_width -<br /> old_column_width + 1);<br /> }<br /> }<br /> }<br /> Here is what the column transition looks like before, during, and after:</div> <div>Copyright © 2002 by The McGraw-HIll Companies, Inc. All rights reserved. Manufactured in the United States of<br /> America. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be<br /> reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior<br /> written permission of the publisher.<br /> 0-07-222858-X<br /> The material in this eBook also appears in the print version of this title: 0-07-222420-7<br /> All trademarks are trademarks of their respective owners. Rather than put a trademark symbol after every occurrence<br /> of a trademarked name, we use names in an editorial fashion only, and to the benefit of the trademark<br /> owner, with no intention of infringement of the trademark. 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Neither McGraw-Hill nor its licensors shall be liable to you or anyone else for<br /> any inaccuracy, error or omission, regardless of cause, in the work or for any damages resulting therefrom.<br /> McGraw-Hill has no responsibility for the content of any information accessed through the work. Under no circumstances<br /> shall McGraw-Hill and/or its licensors be liable for any indirect, incidental, special, punitive, consequential<br /> or similar damages that result from the use of or inability to use the work, even if any of them has been<br /> advised of the possibility of such damages. This limitation of liability shall apply to any claim or cause whatsoever<br /> whether such claim or cause arises in contract, tort or otherwise.<br /> DOI: 10.1036/007222858X</div> <div>Contents<br /> xi<br /> Creating a Multilevel Hierarchy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203<br /> When Constructors Are Called . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207<br /> Method Overriding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208<br /> Dynamic Method Dispatch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211<br /> Why Overridden Methods? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213<br /> Applying Method Overriding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214<br /> Using Abstract Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216<br /> Using final with Inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219<br /> Using final to Prevent Overriding . . . . . . . . . . . . . . . . . . . . . . . . . . 219<br /> Using final to Prevent Inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . 220<br /> The Object Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220<br /> 9 Packages and Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223<br /> Packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224<br /> Defining a Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225<br /> Finding Packages and CLASSPATH . . . . . . . . . . . . . . . . . . . . . . . . 226<br /> A Short Package Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226<br /> Access Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227<br /> An Access Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229<br /> Importing Packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232<br /> Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235<br /> Defining an Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235<br /> Implementing Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236<br /> Applying Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239<br /> Variables in Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243<br /> Interfaces Can Be Extended . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246<br /> 10 Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249<br /> Exception-Handling Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250<br /> Exception Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251<br /> Uncaught Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251<br /> Using try and catch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253<br /> Displaying a Description of an Exception . . . . . . . . . . . . . . . . . . . . 254<br /> Multiple catch Clauses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255<br /> Nested try Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257<br /> throw . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260<br /> throws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261<br /> finally . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263<br /> Java’s Built-in Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265<br /> Creating Your Own Exception Subclasses . . . . . . . . . . . . . . . . . . . . . . . . . . . 267<br /> Chained Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269<br /> Using Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271<br /> 11 Multithreaded Programming . . . . . . . . . . . . . . . . . . . . . . . . . . 273<br /> The Java Thread Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275<br /> Thread Priorities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275<br /> Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276</div> <div>THE JAVA LIBRARY<br /> Chapter 22: Using AWT Controls, Layout Managers, and Menus 763<br /> Here is sample output from the TextAreaDemo applet:<br /> Understanding Layout Managers<br /> All of the components that we have shown so far have been positioned by the default<br /> layout manager. As we mentioned at the beginning of this chapter, a layout manager<br /> automatically arranges your controls within a window by using some type of algorithm.<br /> If you have programmed for other GUI environments, such as Windows, then you are<br /> accustomed to laying out your controls by hand. While it is possible to lay out Java<br /> controls by hand, too, you generally won’t want to, for two main reasons. First, it is very<br /> tedious to manually lay out a large number of components. Second, sometimes the width<br /> and height information is not yet available when you need to arrange some control, because<br /> the native toolkit components haven’t been realized. This is a chicken-and-egg situation;<br /> it is pretty confusing to figure out when it is okay to use the size of a given component to<br /> position it relative to another.<br /> Each Container object has a layout manager associated with it. A layout manager<br /> is an instance of any class that implements the LayoutManager interface. The layout<br /> manager is set by the setLayout( ) method. If no call to setLayout( ) is made, then the<br /> default layout manager is used. Whenever a container is resized (or sized for the first<br /> time), the layout manager is used to position each of the components within it.<br /> The setLayout( ) method has the following general form:<br /> void setLayout(LayoutManager layoutObj)</div> <div>206 Java™ 2: The Complete Reference<br /> new Shipment(10, 20, 15, 10, 3.41);<br /> Shipment shipment2 =<br /> new Shipment(2, 3, 4, 0.76, 1.28);<br /> double vol;<br /> vol = shipment1.volume();<br /> System.out.println("Volume of shipment1 is " + vol);<br /> System.out.println("Weight of shipment1 is "<br /> + shipment1.weight);<br /> System.out.println("Shipping cost: $" + shipment1.cost);<br /> System.out.println();<br /> }<br /> }<br /> vol = shipment2.volume();<br /> System.out.println("Volume of shipment2 is " + vol);<br /> System.out.println("Weight of shipment2 is "<br /> + shipment2.weight);<br /> System.out.println("Shipping cost: $" + shipment2.cost);<br /> The output of this program is shown here:<br /> Volume of shipment1 is 3000.0<br /> Weight of shipment1 is 10.0<br /> Shipping cost: $3.41<br /> Volume of shipment2 is 24.0<br /> Weight of shipment2 is 0.76<br /> Shipping cost: $1.28<br /> Because of inheritance, Shipment can make use of the previously defined classes of<br /> Box and BoxWeight, adding only the extra information it needs for its own, specific<br /> application. This is part of the value of inheritance; it allows the reuse of code.<br /> This example illustrates one other important point: super( ) always refers to the<br /> constructor in the closest superclass. The super( ) in Shipment calls the constructor<br /> in BoxWeight. The super( ) in BoxWeight calls the constructor in Box. In a class<br /> hierarchy, if a superclass constructor requires parameters, then all subclasses must pass<br /> those parameters “up the line.” This is true whether or not a subclass needs parameters<br /> of its own.</div> <div>xxviii Java™ 2: The Complete Reference<br /> For Further Study<br /> Java 2: The Complete Reference is your gateway to the Herb Schildt series of programming<br /> books. Here are some others that you will find of interest:<br /> To learn more about Java programming, we recommend the following:<br /> Java 2: A Beginner's Guide<br /> Java 2 Programmer's Reference<br /> To learn about C++, you will find these books especially helpful:<br /> C++: The Complete Reference<br /> C++: A Beginner's Guide<br /> Teach Yourself C++<br /> C++ From the Ground Up<br /> STL Programming From the Ground Up<br /> To learn about C#, we suggest the following Schildt books:<br /> C#: A Beginner's Guide<br /> C#: The Complete Reference<br /> If you want to learn more about the C language, the foundation of all modern<br /> programming, then the following titles will be of interest:<br /> C: The Complete Reference<br /> Teach Yourself C<br /> When you need solid answers, fast, turn to Herbert Schildt,<br /> the recognized authority on programming.</div> <div>THE JAVA LIBRARY<br /> Chapter 24: New I/O, Regular Expressions, and Other Packages 875<br /> The third source file, AddServer.java, contains the main program for the server<br /> machine. Its primary function is to update the RMI registry on that machine. This is<br /> done by using the rebind( ) method of the Naming class (found in java.rmi). That<br /> method associates a name with an object reference. The first argument to the rebind( )<br /> method is a string that names the server as “AddServer”. Its second argument is a<br /> reference to an instance of AddServerImpl.<br /> import java.net.*;<br /> import java.rmi.*;<br /> public class AddServer {<br /> public static void main(String args[]) {<br /> try {<br /> AddServerImpl addServerImpl = new AddServerImpl();<br /> Naming.rebind("AddServer", addServerImpl);<br /> }<br /> catch(Exception e) {<br /> System.out.println("Exception: " + e);<br /> }<br /> }<br /> }<br /> The fourth source file, AddClient.java, implements the client side of this<br /> distributed application. AddClient.java requires three command line arguments. The<br /> first is the IP address or name of the server machine. The second and third arguments<br /> are the two numbers that are to be summed.<br /> The application begins by forming a string that follows the URL syntax. This URL<br /> uses the rmi protocol. The string includes the IP address or name of the server and the<br /> string “AddServer”. The program then invokes the lookup( ) method of the Naming<br /> class. This method accepts one argument, the rmi URL, and returns a reference to an<br /> object of type AddServerIntf. All remote method invocations can then be directed to<br /> this object.<br /> The program continues by displaying its arguments and then invokes the remote<br /> add( ) method. The sum is returned from this method and is then printed.<br /> import java.rmi.*;<br /> public class AddClient {<br /> public static void main(String args[]) {<br /> try {<br /> String addServerURL = "rmi://" + args[0] + "/AddServer";<br /> AddServerIntf addServerIntf =<br /> (AddServerIntf)Naming.lookup(addServerURL);<br /> System.out.println("The first number is: " + args[1]);</div> <div>APPLYING JAVA<br /> Chapter 32: Scrabblet: A Multiplayer Word Game 1083<br /> available players, so must we call server.delete( ). We take the first turn by setting<br /> ourturn to true.<br /> // our challenge was accepted.<br /> void accept(String id, int seed) {<br /> ourturn = true;<br /> others_name = getName(id);<br /> server.delete();<br /> start_Game(seed);<br /> }<br /> chat( )<br /> The chat( ) method is called by the server whenever the opponent types in his or her<br /> chat window. In this implementation, the method simply shows the chat message in<br /> the browser’s status message. In the future, it might be nice to log these into a<br /> TextArea.<br /> void chat(String id, String s) {<br /> showStatus(others_name + ": " + s);<br /> }<br /> move( )<br /> The move( ) method is called once for each tile your opponent plays. It looks through<br /> the letters saved in theirs to find the one used. If the square is already occupied, the tile<br /> is returned to the player’s tray. Otherwise, the opponent’s letter is moved onto the<br /> board permanently. Next, the tile is replaced in theirs by bag.takeOut( ). If the bag is<br /> empty, a status message appears. The board is repainted to show the new tiles on it.<br /> Note that no scoring is done based on the placement of these tiles. The applet waits<br /> until turn( ) is called to give the score.<br /> // the other guy moved, and placed 'letter' at (x, y).<br /> void move(String letter, int x, int y) {<br /> for (int i = 0; i < 7; i++) {<br /> if (theirs[i] != null && theirs[i].getSymbol().equals(letter)) {<br /> Letter already = board.getLetter(x, y);<br /> if (already != null) {<br /> board.moveLetter(already, 15, 15); // on the tray.<br /> }<br /> board.moveLetter(theirs[i], x, y);</div> <div>THE JAVA LIBRARY<br /> Chapter 17: Input/Output: Exploring java.io 555<br /> Filtered Byte Streams<br /> Filtered streams are simply wrappers around underlying input or output streams that<br /> transparently provide some extended level of functionality. These streams are typically<br /> accessed by methods that are expecting a generic stream, which is a superclass of the<br /> filtered streams. Typical extensions are buffering, character translation, and raw data<br /> translation. The filtered byte streams are FilterInputStream and FilterOutputStream.<br /> Their constructors are shown here:<br /> FilterOutputStream(OutputStream os)<br /> FilterInputStream(InputStream is)<br /> The methods provided in these classes are identical to those in InputStream and<br /> OutputStream.<br /> Buffered Byte Streams<br /> For the byte-oriented streams, a buffered stream extends a filtered stream class by attaching a<br /> memory buffer to the I/O streams. This buffer allows Java to do I/O operations on more<br /> than a byte at a time, hence increasing performance. Because the buffer is available,<br /> skipping, marking, and resetting of the stream becomes possible. The buffered byte stream<br /> classes are BufferedInputStream and BufferedOutputStream. PushbackInputStream also<br /> implements a buffered stream.<br /> BufferedInputStream<br /> Buffering I/O is a very common performance optimization. Java’s BufferedInputStream<br /> class allows you to “wrap” any InputStream into a buffered stream and achieve this<br /> performance improvement.<br /> BufferedInputStream has two constructors:<br /> BufferedInputStream(InputStream inputStream)<br /> BufferedInputStream(InputStream inputStream, int bufSize)<br /> The first form creates a buffered stream using a default buffer size. In the second, the<br /> size of the buffer is passed in bufSize. Use of sizes that are multiples of memory page,<br /> disk block, and so on can have a significant positive impact on performance. This is,<br /> however, implementation-dependent. An optimal buffer size is generally dependent on<br /> the host operating system, the amount of memory available, and how the machine is<br /> configured. To make good use of buffering doesn’t necessarily require quite this degree<br /> of sophistication. A good guess for a size is around 8,192 bytes, and attaching even a<br /> rather small buffer to an I/O stream is always a good idea. That way, the low-level<br /> system can read blocks of data from the disk or network and store the results in your<br /> buffer. Thus, even if you are reading the data a byte at a time out of the InputStream,<br /> you will be manipulating fast memory over 99.9 percent of the time.</div> <div>Chapter 26<br /> A Tour of Swing<br /> 921</div> <div>498 Java™ 2: The Complete Reference<br /> Set set = balance.keySet(); // get set-view of keys<br /> // get iterator<br /> Iterator itr = set.iterator();<br /> while(itr.hasNext()) {<br /> str = (String) itr.next();<br /> System.out.println(str + ": " +<br /> balance.get(str));<br /> }<br /> System.out.println();<br /> }<br /> }<br /> // Deposit 1,000 into John Doe's account<br /> bal = ((Double)balance.get("John Doe")).doubleValue();<br /> balance.put("John Doe", new Double(bal+1000));<br /> System.out.println("John Doe's new balance: " +<br /> balance.get("John Doe"));<br /> Properties<br /> Properties is a subclass of Hashtable.Itisused to maintain lists of values in which the<br /> key is a String and the value is also a String. The Properties class is used by many other<br /> Java classes. For example, it is the type of object returned by System.getProperties( )<br /> when obtaining environmental values.<br /> Properties defines the following instance variable:<br /> Properties defaults;<br /> This variable holds a default property list associated with a Properties object.<br /> Properties defines these constructors:<br /> Properties( )<br /> Properties(Properties propDefault)<br /> The first version creates a Properties object that has no default values. The second<br /> creates an object that uses propDefault for its default values. In both cases, the property<br /> list is empty.<br /> In addition to the methods that Properties inherits from Hashtable, Properties<br /> defines the methods listed in Table 15-14. Properties also contains one deprecated<br /> method: save( ). This was replaced by store( ) because save( ) did not handle errors<br /> correctly.</div> <div>THE JAVA LIBRARY<br /> Chapter 24: New I/O, Regular Expressions, and Other Packages 849<br /> All buffers support various get( ) and put( ) methods, which allow you to get data<br /> from a buffer or put data into a buffer. For example, Table 24-3 shows the get( ) and<br /> Method<br /> abstract byte get( )<br /> ByteBuffer get(byte vals[ ] )<br /> ByteBuffer get(byte vals[ ], int start,<br /> int num)<br /> abstract byte get(int idx)<br /> abstract ByteBuffer put(byte b)<br /> final ByteBuffer put(byte vals[ ] )<br /> ByteBuffer put(byte vals[ ], int start,<br /> int num)<br /> ByteBuffer put(ByteBuffer bb)<br /> abstract ByteBuffer put(int idx, byte b)<br /> Description<br /> Returns the byte at the current position.<br /> Copies the invoking buffer into the array<br /> referred to by vals. Returns a reference to<br /> the buffer.<br /> Copies num elements from the invoking<br /> buffer into the array referred to by vals,<br /> beginning at the index specified by start.<br /> Returns a reference to the buffer. If there<br /> are not num elements remaining in the<br /> buffer, a BufferUnderflowException is<br /> thrown.<br /> Returns the byte at the index specified by<br /> idx within the invoking buffer.<br /> Copies b into the invoking buffer at the<br /> current position. Returns a reference to<br /> the buffer.<br /> Copies all elements of vals into the<br /> invoking buffer, beginning at the current<br /> position. Returns a reference to the buffer.<br /> Copies num elements from vals,<br /> beginning at start, into the invoking<br /> buffer. Returns a reference to the buffer. If<br /> the buffer cannot hold all of the elements,<br /> a BufferOverflowException is thrown.<br /> Copies the elements in bb to the invoking<br /> buffer, beginning at the current position.<br /> If the buffer cannot hold all of the<br /> elements, a BufferOverflowException is<br /> thrown. Returns a reference to the buffer.<br /> Copies b into the invoking buffer at the<br /> location specified by idx. Returns a<br /> reference to the buffer.<br /> Table 24-3.<br /> The get( ) and put( ) methods defined for ByteBuffer</div> <div>THE JAVA LIBRARY<br /> Chapter 18: Networking 615<br /> }<br /> fmt02d(tzhour) + fmt02d(tzmin) +<br /> "] \"" +<br /> cmd + " " +<br /> url + " HTTP/1.0\" " +<br /> code + " " +<br /> size + "\n");<br /> hits_served++;<br /> bytes_served += size;<br /> private void writeString(OutputStream out, String s)<br /> throws IOException {<br /> out.write(toBytes(s));<br /> }<br /> private void writeUCE(OutputStream out, UrlCacheEntry uce)<br /> throws IOException {<br /> HttpResponse hr = new HttpResponse(200, "OK", uce.mh);<br /> writeString(out, hr.toString());<br /> out.write(uce.data, 0, uce.length);<br /> logEntry("GET", uce.url, 200, uce.length);<br /> }<br /> private boolean serveFromCache(OutputStream out, String url)<br /> throws IOException {<br /> UrlCacheEntry uce;<br /> if ((uce = (UrlCacheEntry)cache.get(url)) != null) {<br /> writeUCE(out, uce);<br /> hits_to_cache++;<br /> return true;<br /> }<br /> return false;<br /> }<br /> private UrlCacheEntry loadFile(InputStream in, String url,<br /> MimeHeader mh)<br /> throws IOException {<br /> UrlCacheEntry uce;<br /> byte file_buf[] = new byte[buffer_size];<br /> uce = new UrlCacheEntry(url, mh);</div> <div>THE JAVA LIBRARY<br /> Chapter 24: New I/O, Regular Expressions, and Other Packages 881<br /> The argument formatString describes how date and time information is displayed. An<br /> example of its use is given here:<br /> SimpleDateFormat sdf = SimpleDateFormat("dd MMM yyyy hh:mm:ss zzz");<br /> The symbols used in the formatting string determine the information that is displayed.<br /> Table 24-6 lists these symbols and gives a description of each.<br /> In most cases, the number of times a symbol is repeated determines how that data<br /> is presented. Text information is displayed in an abbreviated form if the pattern letter<br /> is repeated less than four times. Otherwise, the unabbreviated form is used. For<br /> Symbol Description<br /> a<br /> AM or PM<br /> d Day of month (1–31)<br /> h Hour in AM/PM (1–12)<br /> k Hour in day (1–24)<br /> m Minute in hour (0–59)<br /> s Second in minute (0–59)<br /> w Week of year (1–52)<br /> y<br /> Year<br /> z<br /> Time zone<br /> D Day of year (1–366)<br /> E<br /> Day of week (for example, Thursday)<br /> F<br /> Day of week in month<br /> G<br /> Era (that is, AD or BC)<br /> H Hour in day (0–23)<br /> K Hour in AM/PM (0–11)<br /> M<br /> Month<br /> S<br /> Millisecond in second<br /> W Week of month (1–5)<br /> Z<br /> Time zone in RFC822 format<br /> Table 24-6.<br /> Formatting String Symbols for SimpleDateFormat</div> <div>THE JAVA LIBRARY<br /> Chapter 21: Introducing the AWT: Working with Windows, Graphics, and Text 707<br /> void fillRoundRect(int top, int left, int width, int height,<br /> int xDiam, int yDiam)<br /> A rounded rectangle has rounded corners. The upper-left corner of the rectangle<br /> is at top,left. The dimensions of the rectangle are specified by width and height. The<br /> diameter of the rounding arc along the X axis is specified by xDiam. The diameter of<br /> the rounding arc along the Y axis is specified by yDiam.<br /> The following applet draws several rectangles:<br /> // Draw rectangles<br /> import java.awt.*;<br /> import java.applet.*;<br /> /*<br /> <applet code="Rectangles" width=300 height=200><br /> </applet><br /> */<br /> public class Rectangles extends Applet {<br /> public void paint(Graphics g) {<br /> g.drawRect(10, 10, 60, 50);<br /> g.fillRect(100, 10, 60, 50);<br /> g.drawRoundRect(190, 10, 60, 50, 15, 15);<br /> g.fillRoundRect(70, 90, 140, 100, 30, 40);<br /> }<br /> }<br /> Sample output from this program is shown here:</div> <div>THE JAVA LIBRARY<br /> Chapter 15: java.util Part 1: The Collections Framework 471<br /> The first form constructs a default LinkedHashMap. The second form initializes<br /> the LinkedHashMap with the elements from m. The third form initializes the capacity.<br /> The fourth form initializes both capacity and fill ratio. The meaning of capacity and fill<br /> ratio are the same as for HashMap. The last form allows you to specify whether the<br /> elements will be stored in the linked list by insertion order, or by order of last access. If<br /> Order is true, then access order is used. If Order is false, then insertion order is used.<br /> LinkedHashMap adds only one method to those defined by HashMap. This<br /> method is removeEldestEntry( ) and it is shown here.<br /> protected boolean removeEldestEntry(Map.Entry e)<br /> This method is called by put( ) and putAll( ). The oldest entry is passed in e.Bydefault, this<br /> method returns false and does nothing. However, if you override this method, then you<br /> can have the LinkedHashMap remove the oldest entry in the map. To do this, have your<br /> override return true.Tokeep the oldest entry, return false.<br /> The IdentityHashMap Class<br /> Java 2, version 1.4 adds the IdentityHashMap class. This class implements AbstractMap.<br /> It is similar to HashMap except that it uses reference equality when comparing elements.<br /> The Java 2 documentation explicitly states that IdentityHashMap is not for general use.<br /> Comparators<br /> Both TreeSet and TreeMap store elements in sorted order. However, it is the<br /> comparator that defines precisely what “sorted order” means. By default, these classes<br /> store their elements by using what Java refers to as “natural ordering,” which is<br /> usually the ordering that you would expect. (A before B, 1 before 2, and so forth.) If<br /> you want to order elements a different way, then specify a Comparator object when<br /> you construct the set or map. Doing so gives you the ability to govern precisely how<br /> elements are stored within sorted collections and maps.<br /> The Comparator interface defines two methods: compare( ) and equals( ). The<br /> compare( ) method, shown here, compares two elements for order:<br /> int compare(Object obj1, Object obj2)<br /> obj1 and obj2 are the objects to be compared. This method returns zero if the objects are<br /> equal. It returns a positive value if obj1 is greater than obj2. Otherwise, a negative value<br /> is returned. The method can throw a ClassCastException if the types of the objects are<br /> not compatible for comparison. By overriding compare( ), you can alter the way that<br /> objects are ordered. For example, to sort in reverse order, you can create a comparator<br /> that reverses the outcome of a comparison.</div> <div>254 Java™ 2: The Complete Reference<br /> A try and its catch statement form a unit. The scope of the catch clause is restricted<br /> to those statements specified by the immediately preceding try statement. A catch<br /> statement cannot catch an exception thrown by another try statement (except in the<br /> case of nested try statements, described shortly). The statements that are protected by<br /> try must be surrounded by curly braces. (That is, they must be within a block.) You<br /> cannot use try on a single statement.<br /> The goal of most well-constructed catch clauses should be to resolve the<br /> exceptional condition and then continue on as if the error had never happened.<br /> For example, in the next program each iteration of the for loop obtains two random<br /> integers. Those two integers are divided by each other, and the result is used to divide<br /> the value 12345. The final result is put into a. If either division operation causes a<br /> divide-by-zero error, it is caught, the value of a is set to zero, and the program<br /> continues.<br /> // Handle an exception and move on.<br /> import java.util.Random;<br /> class HandleError {<br /> public static void main(String args[]) {<br /> int a=0, b=0, c=0;<br /> Random r = new Random();<br /> }<br /> }<br /> for(int i=0; i<32000; i++) {<br /> try {<br /> b = r.nextInt();<br /> c = r.nextInt();<br /> a = 12345 / (b/c);<br /> } catch (ArithmeticException e) {<br /> System.out.println("Division by zero.");<br /> a = 0; // set a to zero and continue<br /> }<br /> System.out.println("a: " + a);<br /> }<br /> Displaying a Description of an Exception<br /> Throwable overrides the toString( ) method (defined by Object) so that it returns a<br /> string containing a description of the exception. You can display this description in a<br /> println( ) statement by simply passing the exception as an argument. For example, the<br /> catch block in the preceding program can be rewritten like this:</div> <div>THE JAVA LIBRARY<br /> Chapter 20: Event Handling 657<br /> used by the delegation event model. Its getID( ) method can be used to determine the<br /> type of the event. The signature of this method is shown here:<br /> int getID( )<br /> Additional details about AWTEvent are provided at the end of Chapter 22. At this<br /> point, it is important to know only that all of the other classes discussed in this section<br /> are subclasses of AWTEvent.<br /> To summarize:<br /> ■ EventObject is a superclass of all events.<br /> ■ AWTEvent is a superclass of all AWT events that are handled by the delegation<br /> event model.<br /> The package java.awt.event defines several types of events that are generated by<br /> various user interface elements. Table 20-1 enumerates the most important of these event<br /> classes and provides a brief description of when they are generated. The most commonly<br /> used constructors and methods in each class are described in the following sections.<br /> Event Class<br /> ActionEvent<br /> AdjustmentEvent<br /> ComponentEvent<br /> ContainerEvent<br /> FocusEvent<br /> InputEvent<br /> ItemEvent<br /> Description<br /> Generated when a button is pressed, a list item is<br /> double-clicked, or a menu item is selected.<br /> Generated when a scroll bar is manipulated.<br /> Generated when a component is hidden, moved, resized,<br /> or becomes visible.<br /> Generated when a component is added to or removed<br /> from a container.<br /> Generated when a component gains or loses<br /> keyboard focus.<br /> Abstract super class for all component input event classes.<br /> Generated when a check box or list item is clicked; also<br /> occurs when a choice selection is made or a checkable<br /> menu item is selected or deselected.<br /> Table 20-1.<br /> Main Event Classes in java.awt.event</div> <div>118 Java™ 2: The Complete Reference<br /> }<br /> // ...<br /> if(interrupted()) done = true;<br /> In this example, the for loop continues to run until the boolean variable done is set<br /> to true. It does not test the value of i.<br /> Here is another interesting for loop variation. Either the initialization or the<br /> iteration expression or both may be absent, as in this next program:<br /> // Parts of the for loop can be empty.<br /> class ForVar {<br /> public static void main(String args[]) {<br /> int i;<br /> boolean done = false;<br /> }<br /> }<br /> i = 0;<br /> for( ; !done; ) {<br /> System.out.println("i is " + i);<br /> if(i == 10) done = true;<br /> i++;<br /> }<br /> Here, the initialization and iteration expressions have been moved out of the for. Thus,<br /> parts of the for are empty. While this is of no value in this simple example—indeed, it<br /> would be considered quite poor style—there can be times when this type of approach<br /> makes sense. For example, if the initial condition is set through a complex expression<br /> elsewhere in the program or if the loop control variable changes in a nonsequential<br /> manner determined by actions that occur within the body of the loop, it may be<br /> appropriate to leave these parts of the for empty.<br /> Here is one more for loop variation. You can intentionally create an infinite loop<br /> (a loop that never terminates) if you leave all three parts of the for empty. For example:<br /> for( ; ; ) {<br /> // ...<br /> }<br /> This loop will run forever, because there is no condition under which it will terminate.<br /> Although there are some programs, such as operating system command processors,</div> <div>850 Java™ 2: The Complete Reference<br /> put( ) methods defined by ByteBuffer. (The other buffer classes have similar methods.)<br /> All buffer classes also support methods that perform various buffer operations. For<br /> example, you can allocate a buffer manually using allocate( ). You can wrap an array<br /> inside a buffer using wrap( ). You can create a subsequence of a buffer using slice( ).<br /> Channels<br /> Channels are defined in java.nio.channels.Achannel represents an open connection to an<br /> I/O source or destination. You obtain a channel by calling getChannel( ) on an object that<br /> supports channels. Java 2, version 1.4 added getChannel( ) to the following I/O classes.<br /> FileInputStream FileOutputStream RandomAccessFile<br /> Socket ServerSocket DatagramSocket<br /> Thus, to obtain a channel, you first obtain an object of one of these classes and then call<br /> getChannel( ) on that object.<br /> The specific type of channel returned depends upon the type of object getChannel( )<br /> is called on. For example, when called on a FileInputStream, FileOuputStream, or<br /> RandomAccessFile, getChannel( ) returns a channel of type FileChannel. When called<br /> on a Socket, getChannel( ) returns a SocketChannel.<br /> Channels such as FileChannel and SocketChannel support various read( ) and<br /> write( ) methods that enable you to perform I/O operations through the channel. For<br /> example, here are a few of the read( ) and write( ) methods defined for FileChannel.<br /> All can throw an IOException.<br /> Method<br /> abstract int read(ByteBuffer bb)<br /> abstract int read(ByteBuffer bb,<br /> long start)<br /> abstract int write(ByteBuffer bb)<br /> abstract int write(ByteBuffer bb,<br /> long start)<br /> Description<br /> Reads bytes from the invoking channel into bb<br /> until the buffer is full, or there is no more input.<br /> Returns the number of bytes actually read.<br /> Beginning at the file location specified by start,<br /> reads bytes from the invoking channel into<br /> bb until the buffer is full, or there is no more<br /> input. The current position is unchanged.<br /> Returns the number of bytes actually read,<br /> or –1 if start is beyond the end of the file.<br /> Writes the contents of bb to the invoking<br /> channel, starting at the current position.<br /> Returns the number of bytes written.<br /> Beginning at the file location specified by<br /> start, writes the contents of bb to the invoking<br /> channel. The current position is unchanged.<br /> Returns the number of bytes written.</div> <div>THE JAVA LIBRARY<br /> Chapter 19: The Applet Class 651<br /> at the specified URL. The method showDocument(URL, where) displays the specified<br /> document at the specified location within the browser window. Valid arguments for<br /> where are “_self” (show in current frame), “_parent” (show in parent frame), “_top”<br /> (show in topmost frame), and “_blank” (show in new browser window). You can also<br /> specify a name, which causes the document to be shown in a new browser window by<br /> that name.<br /> The following applet demonstrates AppletContext and showDocument( ).<br /> Upon execution, it obtains the current applet context and uses that context to<br /> transfer control to a file called Test.html. This file must be in the same directory<br /> as the applet. Test.html can contain any valid hypertext that you like.<br /> /* Using an applet context, getCodeBase(),<br /> and showDocument() to display an HTML file.<br /> */<br /> import java.awt.*;<br /> import java.applet.*;<br /> import java.net.*;<br /> /*<br /> <applet code="ACDemo" width=300 height=50><br /> </applet><br /> */<br /> public class ACDemo extends Applet{<br /> public void start() {<br /> AppletContext ac = getAppletContext();<br /> URL url = getCodeBase(); // get url of this applet<br /> }<br /> }<br /> try {<br /> ac.showDocument(new URL(url+"Test.html"));<br /> } catch(MalformedURLException e) {<br /> showStatus("URL not found");<br /> }<br /> The AudioClip Interface<br /> The AudioClip interface defines these methods: play( ) (play a clip from the<br /> beginning), stop( ) (stop playing the clip), and loop( ) (play the loop continuously).<br /> After you have loaded an audio clip using getAudioClip( ), you can use these methods<br /> to play it.</div> <div>302 Java™ 2: The Complete Reference<br /> }<br /> }<br /> System.out.println("Press Control-C to stop.");<br /> Inside get( ), wait( ) is called. This causes its execution to suspend until the Producer<br /> notifies you that some data is ready. When this happens, execution inside get( )<br /> resumes. After the data has been obtained, get( ) calls notify( ). This tells Producer that<br /> it is okay to put more data in the queue. Inside put( ), wait( ) suspends execution until<br /> the Consumer has removed the item from the queue. When execution resumes, the<br /> next item of data is put in the queue, and notify( ) is called. This tells the Consumer<br /> that it should now remove it.<br /> Here is some output from this program, which shows the clean synchronous behavior:<br /> Put: 1<br /> Got: 1<br /> Put: 2<br /> Got: 2<br /> Put: 3<br /> Got: 3<br /> Put: 4<br /> Got: 4<br /> Put: 5<br /> Got: 5<br /> Deadlock<br /> A special type of error that you need to avoid that relates specifically to multitasking<br /> is deadlock, which occurs when two threads have a circular dependency on a pair of<br /> synchronized objects. For example, suppose one thread enters the monitor on object X<br /> and another thread enters the monitor on object Y. If the thread in X tries to call any<br /> synchronized method on Y, it will block as expected. However, if the thread in Y, in<br /> turn, tries to call any synchronized method on X, the thread waits forever, because to<br /> access X, it would have to release its own lock on Y so that the first thread could<br /> complete. Deadlock is a difficult error to debug for two reasons:<br /> ■ In general, it occurs only rarely, when the two threads time-slice in just the<br /> right way.<br /> ■ It may involve more than two threads and two synchronized objects. (That is,<br /> deadlock can occur through a more convoluted sequence of events than just<br /> described.)</div> <div>1108 Java™ 2: The Complete Reference<br /> // find the center of the tile<br /> x += dx + lw / 2;<br /> y += dy + lh / 2;<br /> // find the tile index<br /> x = (x - lm) / (lw + lt);<br /> y = (y - tm) / (lh + lt);<br /> moveLetter(pick, x, y);<br /> }<br /> }<br /> pick = null;<br /> repaint();<br /> dragLetter( )<br /> The dragLetter( ) method is handled differently than the other mouse-related events.<br /> This is mainly due to performance considerations. The goal is to have as smooth an<br /> interaction with the user as possible. dragLetter( ) goes to some length to compute the<br /> bounding box of where the tile was before this drag plus where it is now. It then<br /> directly calls paint(getGraphics( )). This is nonstandard Java applet programming, but<br /> it performs much more reliably.<br /> private void dragLetter(int x, int y) {<br /> if (pick != null) {<br /> int ox = pick.x;<br /> int oy = pick.y;<br /> pick.move(x + dx, y + dy);<br /> x0 = Math.min(ox, pick.x);<br /> y0 = Math.min(oy, pick.y);<br /> w0 = pick.w + Math.abs(ox - pick.x);<br /> h0 = pick.h + Math.abs(oy - pick.y);<br /> paint(getGraphics());<br /> }<br /> }<br /> mousePressed( )<br /> In the following code fragment, notice that MyMouseAdapter is an inner class that<br /> extends MouseAdapter. It overrides the mousePressed( ) and mouseReleased( )<br /> methods.</div> <div>THE JAVA LIBRARY<br /> Chapter 17: Input/Output: Exploring java.io 559<br /> }<br /> }<br /> if ((c = f.read()) == '=')<br /> System.out.print(".eq.");<br /> else {<br /> System.out.print("<-");<br /> f.unread(c);<br /> }<br /> break;<br /> default:<br /> System.out.print((char) c);<br /> break;<br /> }<br /> }<br /> Here is the output for this example. Notice that = = was replaced by “.eq.” and = was<br /> replaced by “<–”.<br /> if (a .eq. 4) a <- 0;<br /> PushbackInputStream has the side effect of invalidating the mark( ) or reset( )<br /> methods of the InputStream used to create it. Use markSupported( ) to check any<br /> stream on which you are going to use mark( )/reset( ).<br /> SequenceInputStream<br /> The SequenceInputStream class allows you to concatenate multiple InputStreams.<br /> The construction of a SequenceInputStream is different from any other InputStream.<br /> A SequenceInputStream constructor uses either a pair of InputStreams or an<br /> Enumeration of InputStreams as its argument:<br /> SequenceInputStream(InputStream first, InputStream second)<br /> SequenceInputStream(Enumeration streamEnum)<br /> Operationally, the class fulfills read requests from the first InputStream until it runs<br /> out and then switches over to the second one. In the case of an Enumeration, it will<br /> continue through all of the InputStreams until the end of the last one is reached.<br /> Here is a simple example that uses a SequenceInputStream to output the contents<br /> of two files:<br /> // Demonstrate sequenced input.<br /> import java.io.*;<br /> import java.util.*;</div> <div>974 Java™ 2: The Complete Reference<br /> <option value="Blue">Blue</option><br /> </select><br /> <br><br><br /> <input type=submit value="Submit"><br /> </form><br /> </body><br /> </html><br /> The source code for ColorPostServlet.java is shown in the following listing. The<br /> doPost( ) method is overridden to process any HTTP POST requests that are sent to<br /> this servlet. It uses the getParameter( ) method of HttpServletRequest to obtain the<br /> selection that was made by the user. A response is then formulated.<br /> import java.io.*;<br /> import javax.servlet.*;<br /> import javax.servlet.http.*;<br /> public class ColorPostServlet extends HttpServlet {<br /> public void doPost(HttpServletRequest request,<br /> HttpServletResponse response)<br /> throws ServletException, IOException {<br /> }<br /> }<br /> String color = request.getParameter("color");<br /> response.setContentType("text/html");<br /> PrintWriter pw = response.getWriter();<br /> pw.println("<B>The selected color is: ");<br /> pw.println(color);<br /> pw.close();<br /> Compile the servlet and perform the same steps as described in the previous<br /> section to test it.<br /> Note: Parameters for an HTTP POST request are not included as part of the URL that<br /> is sent to the Web server. In this example, the URL sent from the browser to the server is:<br /> http://localhost:8080/examples/servlet/ColorGetServlet<br /> The parameter names and values are sent in the body of the HTTP request.</div> <div>912 Java™ 2: The Complete Reference<br /> Figure 25-6.<br /> The Bean Builder Windows<br /> called the design window (or, designer for short), is the window in which you will<br /> assemble various components into an application.<br /> In general, to build an application, you will select items from a palette and<br /> instantiate them on the designer, setting their properties as necessary by using the<br /> Property Inspector window. Once you have assembled the components, you will wire<br /> them together by dragging a line from one to another. In the process, you will define<br /> the input and output methods that will be called, and what action causes them to be<br /> called. For example, you might wire a push button to a text field, specifying that when<br /> the push button is pressed, the text field will be cleared.</div> <div>886 Java™ 2: The Complete Reference<br /> This chapter provides an overview of an exciting technology that is at the forefront<br /> of Java programming: Java Beans. Beans are important, because they allow you to<br /> build complex systems from software components. These components may be<br /> provided by you or supplied by one or more different vendors. Java Beans defines an<br /> architecture that specifies how these building blocks can operate together.<br /> To better understand the value of Beans, consider the following. Hardware designers<br /> have a wide variety of components that can be integrated together to construct a system.<br /> Resistors, capacitors, and inductors are examples of simple building blocks. Integrated<br /> circuits provide more advanced functionality. All of these different parts can be reused.<br /> It is not necessary or possible to rebuild these capabilities each time a new system is<br /> needed. Also, the same pieces can be used in different types of circuits. This is possible<br /> because the behavior of these components is understood and documented.<br /> Unfortunately, the software industry has not been as successful in achieving the<br /> benefits of reusability and interoperability. Large applications grow in complexity and<br /> become very difficult to maintain and enhance. Part of the problem is that, until recently,<br /> there has not been a standard, portable way to write a software component. To achieve<br /> the benefits of component software, a component architecture is needed that allows<br /> programs to be assembled from software building blocks, perhaps provided by different<br /> vendors. It must also be possible for a designer to select a component, understand its<br /> capabilities, and incorporate it into an application. When a new version of a component<br /> becomes available, it should be easy to incorporate this functionality into existing code.<br /> Fortunately, Java Beans provides just such an architecture.<br /> What Is a Java Bean?<br /> A Java Bean is a software component that has been designed to be reusable in a variety<br /> of different environments. There is no restriction on the capability of a Bean. It may<br /> perform a simple function, such as checking the spelling of a document, or a complex<br /> function, such as forecasting the performance of a stock portfolio. A Bean may be<br /> visible to an end user. One example of this is a button on a graphical user interface.<br /> A Bean may also be invisible to a user. Software to decode a stream of multimedia<br /> information in real time is an example of this type of building block. Finally, a Bean<br /> may be designed to work autonomously on a user’s workstation or to work in<br /> cooperation with a set of other distributed components. Software to generate a pie<br /> chart from a set of data points is an example of a Bean that can execute locally.<br /> However, a Bean that provides real-time price information from a stock or<br /> commodities exchange would need to work in cooperation with other distributed<br /> software to obtain its data.<br /> You will see shortly what specific changes a software developer must make to a<br /> class so that it is usable as a Java Bean. However, one of the goals of the Java designers<br /> was to make it easy to use this technology. Therefore, the code changes are minimal.</div> <div>52 Java™ 2: The Complete Reference<br /> String Literals<br /> String literals in Java are specified like they are in most other languages—by enclosing<br /> a sequence of characters between a pair of double quotes. Examples of string literals are<br /> “Hello World”<br /> “two\nlines”<br /> “\”This is in quotes\””<br /> The escape sequences and octal/hexadecimal notations that were defined for<br /> character literals work the same way inside of string literals. One important thing to<br /> note about Java strings is that they must begin and end on the same line. There is no<br /> line-continuation escape sequence as there is in other languages.<br /> As you may know, in some other languages, including C/C++, strings are implemented<br /> as arrays of characters. However, this is not the case in Java. Strings are actually object<br /> types. As you will see later in this book, because Java implements strings as objects, Java<br /> includes extensive string-handling capabilities that are both powerful and easy to use.<br /> Variables<br /> The variable is the basic unit of storage in a Java program. A variable is defined by<br /> the combination of an identifier, a type, and an optional initializer. In addition, all<br /> variables have a scope, which defines their visibility, and a lifetime. These elements<br /> are examined next.<br /> Declaring a Variable<br /> In Java, all variables must be declared before they can be used. The basic form of<br /> a variable declaration is shown here:<br /> type identifier [ = value][, identifier [= value] ...] ;<br /> The type is one of Java’s atomic types, or the name of a class or interface. (Class and<br /> interface types are discussed later in Part I of this book.) The identifier is the name of the<br /> variable. You can initialize the variable by specifying an equal sign and a value. Keep<br /> in mind that the initialization expression must result in a value of the same (or compatible)<br /> type as that specified for the variable. To declare more than one variable of the<br /> specified type, use a comma-separated list.</div> <div>THE JAVA LIBRARY<br /> Chapter 18: Networking 623<br /> }<br /> }<br /> else {<br /> stop();<br /> }<br /> public void clear_log(String msg) {<br /> m_log.setText(msg + "\n");<br /> }<br /> }<br /> public void log(String msg) {<br /> m_log.append(msg);<br /> status.setText(m_httpd.hits_served + " hits (" +<br /> (m_httpd.bytes_served / 1024) + "K), " +<br /> m_httpd.files_in_cache + " cached files (" +<br /> (m_httpd.bytes_in_cache / 1024) + "K), " +<br /> m_httpd.hits_to_cache + " cached hits");<br /> status.setSize(status.getPreferredSize());<br /> }<br /> In the files httpd.java and HTTP.java, the code is built assuming that the document<br /> root is “c:\www”. You may need to change this value for your configuration. Because<br /> this applet writes to a log file, it can work only if it is trusted. For example, an applet is<br /> trusted if it is accessible from the user’s class path.<br /> Datagrams<br /> For most of your internetworking needs, you will be happy with TCP/IP-style<br /> networking. It provides a serialized, predictable, reliable stream of packet data. This is<br /> not without its cost, however. TCP includes many complicated algorithms for dealing<br /> with congestion control on crowded networks, as well as pessimistic expectations<br /> about packet loss. This leads to a somewhat inefficient way to transport data.<br /> Datagrams provide an alternative.<br /> Datagrams are bundles of information passed between machines. They are<br /> somewhat like a hard throw from a well-trained but blindfolded catcher to the third<br /> baseman. Once the datagram has been released to its intended target, there is no<br /> assurance that it will arrive or even that someone will be there to catch it. Likewise,<br /> when the datagram is received, there is no assurance that it hasn’t been damaged in<br /> transit or that whoever sent it is still there to receive a response.</div> <div>426 Java™ 2: The Complete Reference<br /> Method<br /> static void sleep(long milliseconds)<br /> throws InterruptedException<br /> static void sleep(long milliseconds,<br /> int nanoseconds)<br /> throws InterruptedException<br /> void start( )<br /> String toString( )<br /> static void yield( )<br /> Description<br /> Suspends execution of the<br /> thread for the specified<br /> number of milliseconds.<br /> Suspends execution of the thread for<br /> the specified number of milliseconds<br /> plus nanoseconds.<br /> Starts execution of the thread.<br /> Returns the string equivalent of<br /> a thread.<br /> The calling thread yields the CPU to<br /> another thread.<br /> Table 14-16.<br /> The Methods Defined by Thread (continued)<br /> ThreadGroup<br /> ThreadGroup creates a group of threads. It defines these two constructors:<br /> ThreadGroup(String groupName)<br /> ThreadGroup(ThreadGroup parentOb, String groupName)<br /> For both forms, groupName specifies the name of the thread group. The first version<br /> creates a new group that has the current thread as its parent. In the second form, the<br /> parent is specified by parentOb.<br /> The methods defined by ThreadGroup are shown in Table 14-17. In versions of Java<br /> prior to 2, ThreadGroup also included the methods stop( ), suspend( ), and resume( ).<br /> These have been deprecated by Java 2 because they were inherently unstable.<br /> Thread groups offer a convenient way to manage groups of threads as a unit. This<br /> is particularly valuable in situations in which you want to suspend and resume a<br /> number of related threads. For example, imagine a program in which one set of threads<br /> is used for printing a document, another set is used to display the document on the<br /> screen, and another set saves the document to a disk file. If printing is aborted, you<br /> will want an easy way to stop all threads related to printing. Thread groups offer this</div> <div>596 Java™ 2: The Complete Reference<br /> Java 2, version 1.4 added the getChannel( ) method to Socket. This method returns<br /> a channel connected to the Socket object. Channels are used by the new I/O classes<br /> contained in java.nio. (See Chapter 24.)<br /> Whois<br /> The very simple example that follows opens a connection to a “whois” port on the<br /> InterNIC server, sends the command-line argument down the socket, and then prints the<br /> data that is returned. InterNIC will try to look up the argument as a registered Internet<br /> domain name, then send back the IP address and contact information for that site.<br /> //Demonstrate Sockets.<br /> import java.net.*;<br /> import java.io.*;<br /> class Whois {<br /> public static void main(String args[]) throws Exception {<br /> int c;<br /> Socket s = new Socket("internic.net", 43);<br /> InputStream in = s.getInputStream();<br /> OutputStream out = s.getOutputStream();<br /> String str = (args.length == 0 ? "osborne.com" : args[0]) + "\n";<br /> byte buf[] = str.getBytes();<br /> out.write(buf);<br /> while ((c = in.read()) != -1) {<br /> System.out.print((char) c);<br /> }<br /> s.close();<br /> }<br /> }<br /> If, for example, you obtained information about osborne.com, you’d get something<br /> similar to the following:<br /> Whois Server Version 1.3<br /> Domain names in the .com, .net, and .org domains can now be registered<br /> with many different competing registrars. Go to http://www.internic.net<br /> for detailed information.<br /> Domain Name: OSBORNE.COM<br /> Registrar: NETWORK SOLUTIONS, INC.<br /> Whois Server: whois.networksolutions.com<br /> Referral URL: http://www.networksolutions.com<br /> Name Server: NS1.EPPG.COM<br /> Name Server: NS2.EPPG.COM</div> <div>800 Java™ 2: The Complete Reference<br /> This chapter examines the AWT’s Image class and the java.awt.image package.<br /> Together, they provide support for imaging (the display and manipulation of<br /> graphical images). An image is simply a rectangular graphical object. Images are<br /> a key component of web design. In fact, the inclusion of the <img> tag in the Mosaic<br /> browser at NCSA (National Center for Supercomputer Applications) is what caused<br /> the Web to begin to grow explosively in 1993. This tag was used to include an image<br /> inline with the flow of hypertext. Java expands upon this basic concept, allowing<br /> images to be managed under program control. Because of its importance, Java provides<br /> extensive support for imaging.<br /> Images are objects of the Image class, which is part of the java.awt package. Images<br /> are manipulated using the classes found in the java.awt.image package. There are a<br /> large number of imaging classes and interfaces defined by java.awt.image and it is not<br /> possible to examine them all. Instead, we will focus on those that form the foundation<br /> of imaging. Here are the java.awt.image classes discussed in this chapter:<br /> CropImageFilter<br /> FilteredImageSource<br /> ImageFilter<br /> MemoryImageSource<br /> PixelGrabber<br /> RGBImageFilter<br /> These are the interfaces that we will use.<br /> ImageConsumer ImageObserver ImageProducer<br /> Also examined is the MediaTracker class, which is part of java.awt.<br /> File Formats<br /> Originally, web images could only be in GIF format. The GIF image format was created<br /> by CompuServe in 1987 to make it possible for images to be viewed while online, so it<br /> was well suited to the Internet. GIF images can have only up to 256 colors each. This<br /> limitation caused the major browser vendors to add support for JPEG images in 1995.<br /> The JPEG format was created by a group of photographic experts to store full-colorspectrum,<br /> continuous-tone images. These images, when properly created, can be of<br /> much higher fidelity as well as more highly compressed than a GIF encoding of the<br /> same source image. In almost all cases, you will never care or notice which format is<br /> being used in your programs. The Java image classes abstract the differences behind a<br /> clean interface.</div> <div>440 Java™ 2: The Complete Reference<br /> The java.util package contains one of Java’s most powerful subsystems: collections.<br /> Collections were added by the initial release of Java 2, and enhanced by Java 2,<br /> version 1.4. A collection is a group of objects. The addition of collections caused<br /> fundamental alterations in the structure and architecture of many elements in java.util.<br /> It also expanded the domain of tasks to which the package can be applied. Collections<br /> are a state-of-the-art technology that merits close attention by all Java programmers.<br /> In addition to collections, java.util contains a wide assortment of classes and<br /> interfaces that support a broad range of functionality. These classes and interfaces are<br /> used throughout the core Java packages and, of course, are also available for use in<br /> programs that you write. Their applications include generating pseudorandom numbers,<br /> manipulating date and time, observing events, manipulating sets of bits, and tokenizing<br /> strings. Because of its many features, java.util is one of Java’s most widely used packages.<br /> The java.util classes are listed here.<br /> AbstractCollection (Java 2) EventObject PropertyResourceBundle<br /> AbstractList (Java 2) GregorianCalendar Random<br /> AbstractMap (Java 2) HashMap (Java 2) ResourceBundle<br /> AbstractSequentialList (Java 2) HashSet (Java 2) SimpleTimeZone<br /> AbstractSet (Java 2) Hashtable Stack<br /> ArrayList (Java 2) IdentityHashMap (Java 2, v1.4) StringTokenizer<br /> Arrays (Java 2) LinkedHashMap (Java 2, v1.4) Timer (Java 2, v1.3)<br /> BitSet LinkedHashSet (Java 2, v1.4) TimerTask (Java 2, v1.3)<br /> Calendar LinkedList (Java 2) TimeZone<br /> Collections (Java 2) ListResourceBundle TreeMap (Java 2)<br /> Currency (Java 2, v1.4) Locale TreeSet (Java 2)<br /> Date Observable Vector<br /> Dictionary Properties WeakHashMap (Java 2)<br /> EventListenerProxy (Java 2, v1.4) PropertyPermission (Java 2)<br /> java.util defines the following interfaces. Notice that most were added by Java 2.<br /> Collection (Java 2) List (Java 2) RandomAccess (Java 2, v1.4)<br /> Comparator (Java 2) ListIterator (Java 2) Set (Java 2)<br /> Enumeration Map (Java 2) SortedMap (Java 2)<br /> EventListener Map.Entry (Java 2) SortedSet (Java 2)<br /> Iterator (Java 2)<br /> Observer<br /> </div> <div>90 Java™ 2: The Complete Reference<br /> The following program creates a few integer variables and then uses the shorthand<br /> form of bitwise operator assignments to manipulate the variables:<br /> class OpBitEquals {<br /> public static void main(String args[]) {<br /> int a = 1;<br /> int b = 2;<br /> int c = 3;<br /> }<br /> }<br /> a |= 4;<br /> b >>= 1;<br /> c <<= 1;<br /> a ^= c;<br /> System.out.println("a = " + a);<br /> System.out.println("b = " + b);<br /> System.out.println("c = " + c);<br /> The output of this program is shown here:<br /> a = 3<br /> b = 1<br /> c = 6<br /> Relational Operators<br /> The relational operators determine the relationship that one operand has to the other.<br /> Specifically, they determine equality and ordering. The relational operators are<br /> shown here:<br /> Operator<br /> Result<br /> == Equal to<br /> != Not equal to<br /> > Greater than</div> <div>THE JAVA LIBRARY<br /> Chapter 14: Exploring java.lang 381<br /> passed by value to methods and cannot be directly passed by reference. Also, there is<br /> no way for two methods to refer to the same instance of an int. At times, you will need<br /> to create an object representation for one of these simple types. For example, there are<br /> enumeration classes discussed in Chapter 15 that deal only with objects; to store a<br /> simple type in one of these classes, you need to wrap the simple type in a class. To<br /> address this need, Java provides classes that correspond to each of the simple types. In<br /> essence, these classes encapsulate, or wrap, the simple types within a class. Thus, they<br /> are commonly referred to as type wrappers.<br /> Number<br /> The abstract class Number defines a superclass that is implemented by the classes that<br /> wrap the numeric types byte, short, int, long, float, and double. Number has abstract<br /> methods that return the value of the object in each of the different number formats.<br /> That is, doubleValue( ) returns the value as a double, floatValue( ) returns the value<br /> as a float, and so on. These methods are shown here:<br /> byte byteValue( )<br /> double doubleValue( )<br /> float floatValue( )<br /> int intValue( )<br /> long longValue( )<br /> short shortValue( )<br /> The values returned by these methods can be rounded.<br /> Number has six concrete subclasses that hold explicit values of each numeric type:<br /> Double, Float, Byte, Short, Integer, and Long.<br /> Double and Float<br /> Double and Float are wrappers for floating-point values of type double and float,<br /> respectively. The constructors for Float are shown here:<br /> Float(double num)<br /> Float(float num)<br /> Float(String str) throws NumberFormatException<br /> As you can see, Float objects can be constructed with values of type float or double.<br /> They can also be constructed from the string representation of a floating-point number.<br /> The constructors for Double are shown here:<br /> Double(double num)<br /> Double(String str) throws NumberFormatException<br /> Double objects can be constructed with a double value or a string containing a<br /> floating-point value.</div> <div>THE JAVA LANGUAGE<br /> Chapter 7: A Closer Look at Methods and Classes 181<br /> // push some numbers onto the stack<br /> for(int i=0; i<5; i++) mystack1.push(i);<br /> for(int i=0; i<8; i++) mystack2.push(i);<br /> // pop those numbers off the stack<br /> System.out.println("Stack in mystack1:");<br /> for(int i=0; i<5; i++)<br /> System.out.println(mystack1.pop());<br /> }<br /> }<br /> System.out.println("Stack in mystack2:");<br /> for(int i=0; i<8; i++)<br /> System.out.println(mystack2.pop());<br /> Notice that the program creates two stacks: one five elements deep and the other<br /> eight elements deep. As you can see, the fact that arrays maintain their own length<br /> information makes it easy to create stacks of any size.<br /> Introducing Nested and Inner Classes<br /> It is possible to define a class within another class; such classes are known as nested classes.<br /> The scope of a nested class is bounded by the scope of its enclosing class. Thus, if class B is<br /> defined within class A, then B is known to A, but not outside of A. A nested class has access<br /> to the members, including private members, of the class in which it is nested. However, the<br /> enclosing class does not have access to the members of the nested class.<br /> There are two types of nested classes: static and non-static.Astatic nested class is one<br /> which has the static modifier applied. Because it is static, it must access the members of<br /> its enclosing class through an object. That is, it cannot refer to members of its enclosing<br /> class directly. Because of this restriction, static nested classes are seldom used.<br /> The most important type of nested class is the inner class. An inner class is a<br /> non-static nested class. It has access to all of the variables and methods of its outer class<br /> and may refer to them directly in the same way that other non-static members of the<br /> outer class do. Thus, an inner class is fully within the scope of its enclosing class.<br /> The following program illustrates how to define and use an inner class. The class<br /> named Outer has one instance variable named outer_x, one instance method named<br /> test( ), and defines one inner class called Inner.<br /> // Demonstrate an inner class.<br /> class Outer {<br /> int outer_x = 100;</div> <div>THE JAVA LIBRARY<br /> Chapter 20: Event Handling 683<br /> through the stored applet reference. In other words, showStatus( ) is invoked relative to<br /> the applet reference stored by MyMouseAdapter.<br /> // This applet does NOT use an inner class.<br /> import java.applet.*;<br /> import java.awt.event.*;<br /> /*<br /> <applet code="MousePressedDemo" width=200 height=100><br /> </applet><br /> */<br /> public class MousePressedDemo extends Applet {<br /> public void init() {<br /> addMouseListener(new MyMouseAdapter(this));<br /> }<br /> }<br /> class MyMouseAdapter extends MouseAdapter {<br /> MousePressedDemo mousePressedDemo;<br /> public MyMouseAdapter(MousePressedDemo mousePressedDemo) {<br /> this.mousePressedDemo = mousePressedDemo;<br /> }<br /> public void mousePressed(MouseEvent me) {<br /> mousePressedDemo.showStatus("Mouse Pressed.");<br /> }<br /> }<br /> The following listing shows how the preceding program can be improved<br /> by using an inner class. Here, InnerClassDemo is a top-level class that extends<br /> Applet. MyMouseAdapter is an inner class that extends MouseAdapter. Because<br /> MyMouseAdapter is defined within the scope of InnerClassDemo,ithas access to all of<br /> the variables and methods within the scope of that class. Therefore, the mousePressed( )<br /> method can call the showStatus( ) method directly. It no longer needs to do this via a<br /> stored reference to the applet. Thus, it is no longer necessary to pass MyMouseAdapter( )<br /> a reference to the invoking object.<br /> // Inner class demo.<br /> import java.applet.*;<br /> import java.awt.event.*;<br /> /*<br /> <applet code="InnerClassDemo" width=200 height=100><br /> </applet><br /> */</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 27: Servlets 959<br /> Method<br /> String getRemoteAddr( )<br /> String getRemoteHost( )<br /> String getScheme( )<br /> String getServerName( )<br /> int getServerPort( )<br /> Description<br /> Returns the string equivalent of the<br /> client IP address.<br /> Returns the string equivalent of the<br /> client host name.<br /> Returns the transmission scheme of<br /> the URL used for the request (for<br /> example, “http”, “ftp”).<br /> Returns the name of the server.<br /> Returns the port number.<br /> Table 27-3.<br /> Various Methods Defined by ServletRequest (continued)<br /> Method<br /> String getCharacterEncoding( )<br /> ServletOutputStream<br /> getOutputStream( )<br /> throws IOException<br /> PrintWriter getWriter( )<br /> throws IOException<br /> void setContentLength(int size)<br /> void setContentType(String type)<br /> Description<br /> Returns the character encoding for the<br /> response.<br /> Returns a ServletOutputStream that can be<br /> used to write binary data to the response.<br /> An IllegalStateException is thrown if<br /> getWriter( ) has already been invoked for<br /> this request.<br /> Returns a PrintWriter that can be used<br /> to write character data to the response.<br /> An IllegalStateException is thrown if<br /> getOutputStream( ) has already been<br /> invoked for this request.<br /> Sets the content length for the response to size.<br /> Sets the content type for the response to type.<br /> Table 27-4.<br /> Various Methods Defined by ServletResponse</div> <div>THE JAVA LANGUAGE<br /> Chapter 12: I/O, Applets, and Other Topics 327<br /> For example, to copy a file called FIRST.TXT<br /> to a file called SECOND.TXT, use the following<br /> command line.<br /> */<br /> java CopyFile FIRST.TXT SECOND.TXT<br /> import java.io.*;<br /> class CopyFile {<br /> public static void main(String args[])<br /> throws IOException<br /> {<br /> int i;<br /> FileInputStream fin;<br /> FileOutputStream fout;<br /> try {<br /> // open input file<br /> try {<br /> fin = new FileInputStream(args[0]);<br /> } catch(FileNotFoundException e) {<br /> System.out.println("Input File Not Found");<br /> return;<br /> }<br /> // open output file<br /> try {<br /> fout = new FileOutputStream(args[1]);<br /> } catch(FileNotFoundException e) {<br /> System.out.println("Error Opening Output File");<br /> return;<br /> }<br /> } catch(ArrayIndexOutOfBoundsException e) {<br /> System.out.println("Usage: CopyFile From To");<br /> return;<br /> }<br /> // Copy File<br /> try {<br /> do {<br /> i = fin.read();</div> <div>THE JAVA LANGUAGE<br /> Chapter 11: Multithreaded Programming 283<br /> // Create a second thread by extending Thread<br /> class NewThread extends Thread {<br /> }<br /> NewThread() {<br /> // Create a new, second thread<br /> super("Demo Thread");<br /> System.out.println("Child thread: " + this);<br /> start(); // Start the thread<br /> }<br /> // This is the entry point for the second thread.<br /> public void run() {<br /> try {<br /> for(int i = 5; i > 0; i--) {<br /> System.out.println("Child Thread: " + i);<br /> Thread.sleep(500);<br /> }<br /> } catch (InterruptedException e) {<br /> System.out.println("Child interrupted.");<br /> }<br /> System.out.println("Exiting child thread.");<br /> }<br /> class ExtendThread {<br /> public static void main(String args[]) {<br /> new NewThread(); // create a new thread<br /> }<br /> }<br /> try {<br /> for(int i = 5; i > 0; i--) {<br /> System.out.println("Main Thread: " + i);<br /> Thread.sleep(1000);<br /> }<br /> } catch (InterruptedException e) {<br /> System.out.println("Main thread interrupted.");<br /> }<br /> System.out.println("Main thread exiting.");</div> <div>314 Java™ 2: The Complete Reference<br /> This chapter introduces two of Java’s most important packages: io and applet. The<br /> io package supports Java’s basic I/O (input/output) system, including file I/O.<br /> The applet package supports applets. Support for both I/O and applets comes<br /> from Java’s core API libraries, not from language keywords. For this reason, an<br /> in-depth discussion of these topics is found in Part II of this book, which examines<br /> Java’s API classes. This chapter discusses the foundation of these two subsystems, so<br /> that you can see how they are integrated into the Java language and how they fit into<br /> the larger context of the Java programming and execution environment. This chapter<br /> also examines the last of Java’s keywords: transient, volatile, instanceof, native,<br /> strictfp, and assert.<br /> I/O Basics<br /> As you may have noticed while reading the preceding 11 chapters, not much use has<br /> been made of I/O in the example programs. In fact, aside from print( ) and println( ),<br /> none of the I/O methods have been used significantly. The reason is simple: most real<br /> applications of Java are not text-based, console programs. Rather, they are graphically<br /> oriented applets that rely upon Java’s Abstract Window Toolkit (AWT) for interaction<br /> with the user. Although text-based programs are excellent as teaching examples, they<br /> do not constitute an important use for Java in the real world. Also, Java’s support for<br /> console I/O is limited and somewhat awkward to use—even in simple example<br /> programs. Text-based console I/O is just not very important to Java programming.<br /> The preceding paragraph notwithstanding, Java does provide strong, flexible<br /> support for I/O as it relates to files and networks. Java’s I/O system is cohesive and<br /> consistent. In fact, once you understand its fundamentals, the rest of the I/O system is<br /> easy to master.<br /> Streams<br /> Java programs perform I/O through streams. A stream is an abstraction that either<br /> produces or consumes information. A stream is linked to a physical device by the Java<br /> I/O system. All streams behave in the same manner, even if the actual physical devices<br /> to which they are linked differ. Thus, the same I/O classes and methods can be applied<br /> to any type of device. This means that an input stream can abstract many different<br /> kinds of input: from a disk file, a keyboard, or a network socket. Likewise, an output<br /> stream may refer to the console, a disk file, or a network connection. Streams are a<br /> clean way to deal with input/output without having every part of your code<br /> understand the difference between a keyboard and a network, for example. Java<br /> implements streams within class hierarchies defined in the java.io package.<br /> If you are familiar with C/C++/C#, then you are already familiar with the concept of the<br /> stream. Java’s approach to streams is loosely the same.</div> <div>1066 Java™ 2: The Complete Reference<br /> }<br /> private void rehash() {<br /> int newcapacity = capacity * 2 + 1;<br /> Object newvals[] = new Object[newcapacity];<br /> int newkeys[] = new int[newcapacity];<br /> for (int i = 0; i < capacity; i++) {<br /> Object o = vals[i];<br /> if (o != null) {<br /> int k = keys[i];<br /> int newi = (k & 0x7fffffff) % newcapacity;<br /> while (newvals[newi] != null)<br /> newi = (newi + 1) % newcapacity;<br /> newkeys[newi] = k;<br /> newvals[newi] = o;<br /> }<br /> }<br /> capacity = newcapacity;<br /> keys = newkeys;<br /> vals = newvals;<br /> }<br /> public void put(int k, Object o) {<br /> int i = (k & 0x7fffffff) % capacity;<br /> while (vals[i] != null && k != keys[i]) // hash collision.<br /> i = (i + 1) % capacity;<br /> if (vals[i] == null)<br /> size++;<br /> keys[i] = k;<br /> vals[i] = o;<br /> if (size > (int)(capacity * load))<br /> rehash();<br /> }<br /> public final Object get(int k) {<br /> int i = (k & 0x7fffffff) % capacity;<br /> while (vals[i] != null && k != keys[i]) // hash miss<br /> i = (i + 1) % capacity;<br /> return vals[i];<br /> }</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 28: Migrating from C++ to Java 991<br /> Much C++ code is sprinkled with obscure, difficult to understand pointer expressions.<br /> While these expressions do tend to increase speed of execution, they are one of the<br /> most troubling issues associated with the maintenance of C++ programs. They will also<br /> present difficulty when you convert the code to Java. When you are confronted with a<br /> complex pointer expression, it is sometimes useful to begin by breaking it into its<br /> subexpressions so that its exact operation becomes clear.<br /> C++ Reference Parameters Versus Java<br /> Reference Parameters<br /> In the preceding section, you saw an example of a C++ program that used a pointer<br /> parameter. In Java, this became a reference parameter. Of course, C++ also supports<br /> reference parameters. As mentioned, most pointer parameters found in C++ code<br /> are simply holdovers from C. Nearly all new C++ code will use reference parameters<br /> when a function needs access to the argument, itself. (In essence, pointer parameters,<br /> although still common, are actually anachronisms in most C++ code.) Since both Java<br /> and C++ support reference parameters, you might think that the conversion of a C++<br /> function that uses reference parameters to a Java method would involve few changes.<br /> Unfortunately, this is not always the case. To understand why, let’s convert the<br /> following C++ program, which swaps the contents of two Coord objects using<br /> reference parameters:<br /> // Swap coordinates -- C++ version.<br /> #include <iostream><br /> using namespace std;<br /> class Coord {<br /> public:<br /> int x;<br /> int y;<br /> };<br /> // Swap contents of two Coord objects.<br /> void swap(Coord &a, Coord &b) {<br /> Coord temp;<br /> }<br /> // swap contents of objects<br /> temp = a;<br /> a = b;<br /> b = temp;</div> <div>376 Java™ 2: The Complete Reference<br /> StringBuffer Methods Added by Java 2, Version 1.4<br /> Java 2, version 1.4 added several new methods to StringBuffer. They are summarized<br /> in the following table.<br /> Method<br /> CharSequence<br /> subSequence(int startIndex,<br /> int stopIndex)<br /> int indexOf(String str)<br /> int indexOf(String str, int startIndex)<br /> int lastIndexOf(String str)<br /> int lastIndexOf(String str, int startIndex)<br /> Description<br /> Returns a substring of the invoking<br /> string, beginning at startIndex and<br /> stopping at stopIndex. This method is<br /> required by the CharSequence interface,<br /> which is now implemented by<br /> StringBuffer.<br /> Searches the invoking StringBuffer for<br /> the first occurrence of str. Returns the<br /> index of the match, or –1 if no match is<br /> found.<br /> Searches the invoking StringBuffer for<br /> the first occurrence of str, beginning at<br /> startIndex. Returns the index of the<br /> match, or –1 if no match is found.<br /> Searches the invoking StringBuffer for<br /> the last occurrence of str. Returns the<br /> index of the match, or –1 if no match is<br /> found.<br /> Searches the invoking StringBuffer for<br /> the last occurrence of str, beginning at<br /> startIndex. Returns the index of the<br /> match, or –1 if no match is found.<br /> Aside from subSequence( ), which implements a method required by the<br /> CharSequence interface, the other methods allow a StringBuffer to be searched for an<br /> occurrence of a String. The following program demonstrates indexOf( ) and<br /> lastIndexOf( ).<br /> class IndexOfDemo {<br /> public static void main(String args[]) {<br /> StringBuffer sb = new StringBuffer("one two one");<br /> int i;</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 26: A Tour of Swing 937<br /> import javax.swing.*;<br /> /*<br /> <applet code="JTabbedPaneDemo" width=400 height=100><br /> </applet><br /> */<br /> public class JTabbedPaneDemo extends JApplet {<br /> public void init() {<br /> }<br /> }<br /> JTabbedPane jtp = new JTabbedPane();<br /> jtp.addTab("Cities", new CitiesPanel());<br /> jtp.addTab("Colors", new ColorsPanel());<br /> jtp.addTab("Flavors", new FlavorsPanel());<br /> getContentPane().add(jtp);<br /> class CitiesPanel extends JPanel {<br /> public CitiesPanel() {<br /> }<br /> }<br /> JButton b1 = new JButton("New York");<br /> add(b1);<br /> JButton b2 = new JButton("London");<br /> add(b2);<br /> JButton b3 = new JButton("Hong Kong");<br /> add(b3);<br /> JButton b4 = new JButton("Tokyo");<br /> add(b4);<br /> class ColorsPanel extends JPanel {<br /> public ColorsPanel() {</div> <div>THE JAVA LANGUAGE<br /> Chapter 6: Introducing Classes 137<br /> Assigning Object Reference Variables<br /> Object reference variables act differently than you might expect when an assignment<br /> takes place. For example, what do you think the following fragment does?<br /> Box b1 = new Box();<br /> Box b2 = b1;<br /> You might think that b2 is being assigned a reference to a copy of the object referred<br /> to by b1. That is, you might think that b1 and b2 refer to separate and distinct objects.<br /> However, this would be wrong. Instead, after this fragment executes, b1 and b2 will<br /> both refer to the same object. The assignment of b1 to b2 did not allocate any memory<br /> or copy any part of the original object. It simply makes b2 refer to the same object as<br /> does b1. Thus, any changes made to the object through b2 will affect the object to<br /> which b1 is referring, since they are the same object.<br /> This situation is depicted here:<br /> Although b1 and b2 both refer to the same object, they are not linked in any other<br /> way. For example, a subsequent assignment to b1 will simply unhook b1 from the<br /> original object without affecting the object or affecting b2. For example:<br /> Box b1 = new Box();<br /> Box b2 = b1;<br /> // ...<br /> b1 = null;<br /> Here, b1 has been set to null, but b2 still points to the original object.<br /> When you assign one object reference variable to another object reference variable, you<br /> are not creating a copy of the object, you are only making a copy of the reference.</div> <div>328 Java™ 2: The Complete Reference<br /> if(i != -1) fout.write(i);<br /> } while(i != -1);<br /> } catch(IOException e) {<br /> System.out.println("File Error");<br /> }<br /> }<br /> }<br /> fin.close();<br /> fout.close();<br /> Notice the way that potential I/O errors are handled in this program and in the<br /> preceding ShowFile program. Unlike some other computer languages, including C<br /> and C++, which use error codes to report file errors, Java uses its exception handling<br /> mechanism. Not only does this make file handling cleaner, but it also enables Java to<br /> easily differentiate the end-of-file condition from file errors when input is being<br /> performed. In C/C++, many input functions return the same value when an error<br /> occurs and when the end of the file is reached. (That is, in C/C++, an EOF condition<br /> often is mapped to the same value as an input error.) This usually means that the<br /> programmer must include extra program statements to determine which event actually<br /> occurred. In Java, errors are passed to your program via exceptions, not by values<br /> returned by read( ). Thus, when read( ) returns –1, it means only one thing: the end of<br /> the file has been encountered.<br /> Applet Fundamentals<br /> All of the preceding examples in this book have been Java applications. However,<br /> applications constitute only one class of Java programs. Another type of program is the<br /> applet. As mentioned in Chapter 1, applets are small applications that are accessed on an<br /> Internet server, transported over the Internet, automatically installed, and run as part of a<br /> Web document. After an applet arrives on the client, it has limited access to resources, so<br /> that it can produce an arbitrary multimedia user interface and run complex computations<br /> without introducing the risk of viruses or breaching data integrity.<br /> Many of the issues connected with the creation and use of applets are found in Part<br /> II, when the applet package is examined. However, the fundamentals connected to the<br /> creation of an applet are presented here, because applets are not structured in the same<br /> way as the programs that have been used thus far. As you will see, applets differ from<br /> applications in several key areas.<br /> Let’s begin with the simple applet shown here:</div> <div>THE JAVA LIBRARY<br /> Chapter 22: Using AWT Controls, Layout Managers, and Menus 775<br /> }<br /> cardLO.show(osCards, "Windows");<br /> }<br /> else {<br /> cardLO.show(osCards, "Other");<br /> }<br /> }<br /> Following is the output generated by the CardLayoutDemo applet. Each card is activated<br /> by pushing its button. You can also cycle through the cards by clicking the mouse.<br /> Menu Bars and Menus<br /> A top-level window can have a menu bar associated with it. A menu bar displays<br /> a list of top-level menu choices. Each choice is associated with a drop-down menu.<br /> This concept is implemented in Java by the following classes: MenuBar, Menu, and<br /> MenuItem. In general, a menu bar contains one or more Menu objects. Each Menu<br /> object contains a list of MenuItem objects. Each MenuItem object represents something<br /> that can be selected by the user. Since Menu is a subclass of MenuItem, a hierarchy of<br /> nested submenus can be created. It is also possible to include checkable menu items.<br /> These are menu options of type CheckboxMenuItem and will have a check mark next<br /> to them when they are selected.</div> <div>94 Java™ 2: The Complete Reference<br /> operator results in false when A is false, no matter what B is. If you use the || and<br /> && forms, rather than the | and & forms of these operators, Java will not bother to<br /> evaluate the right-hand operand when the outcome of the expression can be determined<br /> by the left operand alone. This is very useful when the right-hand operand depends on<br /> the left one being true or false in order to function properly. For example, the following<br /> code fragment shows how you can take advantage of short-circuit logical evaluation to<br /> be sure that a division operation will be valid before evaluating it:<br /> if (denom != 0 && num / denom > 10)<br /> Since the short-circuit form of AND (&&) is used, there is no risk of causing a<br /> run-time exception when denom is zero. If this line of code were written using the<br /> single & version of AND, both sides would have to be evaluated, causing a run-time<br /> exception when denom is zero.<br /> It is standard practice to use the short-circuit forms of AND and OR in cases<br /> involving Boolean logic, leaving the single-character versions exclusively for bitwise<br /> operations. However, there are exceptions to this rule. For example, consider the<br /> following statement:<br /> if(c==1 & e++ < 100) d = 100;<br /> Here, using a single & ensures that the increment operation will be applied to e whether<br /> c is equal to 1 or not.<br /> The Assignment Operator<br /> You have been using the assignment operator since Chapter 2. Now it is time to take<br /> a formal look at it. The assignment operator is the single equal sign, =. The assignment<br /> operator works in Java much as it does in any other computer language. It has this<br /> general form:<br /> var = expression;<br /> Here, the type of var must be compatible with the type of expression.<br /> The assignment operator does have one interesting attribute that you may not be<br /> familiar with: it allows you to create a chain of assignments. For example, consider<br /> this fragment:</div> <div>456 Java™ 2: The Complete Reference<br /> }<br /> System.out.println(hs);<br /> }<br /> The following is the output from this program:<br /> [A, F, E, D, C, B]<br /> As explained, the elements are not stored in sorted order, and the precise output may vary.<br /> The LinkedHashSet Class<br /> Java 2, version 1.4 adds the LinkedHashSet class. This class extends HashSet, but adds<br /> no members of its own. LinkedHashSet maintains a linked list of the entries in the set,<br /> in the order in which they were inserted. This allows insertion-order iteration over the<br /> set. That is, when cycling through a LinkedHashSet using an iterator, the elements will<br /> be returned in the order in which they were inserted. This is also the order in which<br /> they are contained in the string returned by toString( ) when called on a LinkedHashSet<br /> object. To see the effect of LinkedHashSet, try substituting LinkedHashSet For HashSet<br /> in the preceding program. The output will be<br /> [B, A, D, E, C, F]<br /> which is the order in which the elements were inserted.<br /> The TreeSet Class<br /> TreeSet provides an implementation of the Set interface that uses a tree for storage.<br /> Objects are stored in sorted, ascending order. Access and retrieval times are quite fast,<br /> which makes TreeSet an excellent choice when storing large amounts of sorted<br /> information that must be found quickly.<br /> The following constructors are defined:<br /> TreeSet( )<br /> TreeSet(Collection c)<br /> TreeSet(Comparator comp)<br /> TreeSet(SortedSet ss)<br /> The first form constructs an empty tree set that will be sorted in ascending order<br /> according to the natural order of its elements. The second form builds a tree set that<br /> contains the elements of c. The third form constructs an empty tree set that will be<br /> sorted according to the comparator specified by comp. (Comparators are described later<br /> in this chapter.) The fourth form builds a tree set that contains the elements of ss.</div> <div>298 Java™ 2: The Complete Reference<br /> These methods are declared within Object, as shown here:<br /> final void wait( ) throws InterruptedException<br /> final void notify( )<br /> final void notifyAll( )<br /> Additional forms of wait( ) exist that allow you to specify a period of time to wait.<br /> The following sample program incorrectly implements a simple form of the<br /> producer/consumer problem. It consists of four classes: Q, the queue that you’re<br /> trying to synchronize; Producer, the threaded object that is producing queue entries;<br /> Consumer, the threaded object that is consuming queue entries; and PC, the tiny<br /> class that creates the single Q, Producer, and Consumer.<br /> // An incorrect implementation of a producer and consumer.<br /> class Q {<br /> int n;<br /> }<br /> synchronized int get() {<br /> System.out.println("Got: " + n);<br /> return n;<br /> }<br /> synchronized void put(int n) {<br /> this.n = n;<br /> System.out.println("Put: " + n);<br /> }<br /> class Producer implements Runnable {<br /> Q q;<br /> Producer(Q q) {<br /> this.q = q;<br /> new Thread(this, "Producer").start();<br /> }<br /> public void run() {<br /> int i = 0;<br /> while(true) {<br /> q.put(i++);</div> <div>THE JAVA LANGUAGE<br /> Chapter 2: An Overview of Java 37<br /> As you will see later in this book, blocks of code have additional properties and<br /> uses. However, the main reason for their existence is to create logically inseparable<br /> units of code.<br /> Lexical Issues<br /> Now that you have seen several short Java programs, it is time to more formally<br /> describe the atomic elements of Java. Java programs are a collection of whitespace,<br /> identifiers, comments, literals, operators, separators, and keywords. The operators<br /> are described in the next chapter. The others are described next.<br /> Whitespace<br /> Java is a free-form language. This means that you do not need to follow any special<br /> indentation rules. For example, the Example program could have been written all on<br /> one line or in any other strange way you felt like typing it, as long as there was at least<br /> one whitespace character between each token that was not already delineated by an<br /> operator or separator. In Java, whitespace is a space, tab, or newline.<br /> Identifiers<br /> Identifiers are used for class names, method names, and variable names. An identifier<br /> may be any descriptive sequence of uppercase and lowercase letters, numbers, or the<br /> underscore and dollar-sign characters. They must not begin with a number, lest they be<br /> confused with a numeric literal. Again, Java is case-sensitive, so VALUE is a different<br /> identifier than Value. Some examples of valid identifiers are:<br /> AvgTemp count a4 $test this_is_ok<br /> Invalid variable names include:<br /> 2count high-temp Not/ok<br /> Literals<br /> A constant value in Java is created by using a literal representation of it. For example,<br /> here are some literals:<br /> 100 98.6 ‘X’ “This is a test”<br /> Left to right, the first literal specifies an integer, the next is a floating-point value, the<br /> third is a character constant, and the last is a string. A literal can be used anywhere<br /> a value of its type is allowed.</div> <div>658 Java™ 2: The Complete Reference<br /> Event Class<br /> KeyEvent<br /> MouseEvent<br /> MouseWheelEvent<br /> TextEvent<br /> WindowEvent<br /> Description<br /> Generated when input is received from the keyboard.<br /> Generated when the mouse is dragged, moved, clicked,<br /> pressed, or released; also generated when the mouse enters<br /> or exits a component.<br /> Generated when the mouse wheel is moved. (Added by<br /> Java 2, version 1.4)<br /> Generated when the value of a text area or text field is<br /> changed.<br /> Generated when a window is activated, closed, deactivated,<br /> deiconified, iconified, opened, or quit.<br /> Table 20-1.<br /> Main Event Classes in java.awt.event (continued)<br /> The ActionEvent Class<br /> An ActionEvent is generated when a button is pressed, a list item is double-clicked,<br /> or a menu item is selected. The ActionEvent class defines four integer constants that<br /> can be used to identify any modifiers associated with an action event: ALT_MASK,<br /> CTRL_MASK, META_MASK, and SHIFT_MASK. In addition, there is an integer<br /> constant, ACTION_PERFORMED, which can be used to identify action events.<br /> ActionEvent has these three constructors:<br /> ActionEvent(Object src, int type, String cmd)<br /> ActionEvent(Object src, int type, String cmd, int modifiers)<br /> ActionEvent(Object src, int type, String cmd, long when, int modifiers)<br /> Here, src is a reference to the object that generated this event. The type of the event<br /> is specified by type, and its command string is cmd. The argument modifiers indicates<br /> which modifier keys (ALT, CTRL, META, and/or SHIFT) were pressed when the event<br /> was generated. The when parameter specifies when the event occurred. The third<br /> constructor was added by Java 2, version 1.4.<br /> You can obtain the command name for the invoking ActionEvent object by using<br /> the getActionCommand( ) method, shown here:<br /> String getActionCommand( )<br /> For example, when a button is pressed, an action event is generated that has a command<br /> name equal to the label on that button.<br /> The getModifiers( ) method returns a value that indicates which modifier keys<br /> (ALT, CTRL, META, and/or SHIFT) were pressed when the event was generated. Its form<br /> is shown here:</div> <div>48 Java™ 2: The Complete Reference<br /> This program displays the following output:<br /> ch1 and ch2: X Y<br /> Notice that ch1 is assigned the value 88, which is the ASCII (and Unicode) value that<br /> corresponds to the letter X. As mentioned, the ASCII character set occupies the first<br /> 127 values in the Unicode character set. For this reason, all the “old tricks” that you<br /> have used with characters in the past will work in Java, too.<br /> Even though chars are not integers, in many cases you can operate on them as if<br /> they were integers. This allows you to add two characters together, or to increment<br /> the value of a character variable. For example, consider the following program:<br /> // char variables behave like integers.<br /> class CharDemo2 {<br /> public static void main(String args[]) {<br /> char ch1;<br /> ch1 = 'X';<br /> System.out.println("ch1 contains " + ch1);<br /> }<br /> }<br /> ch1++; // increment ch1<br /> System.out.println("ch1 is now " + ch1);<br /> The output generated by this program is shown here:<br /> ch1 contains X<br /> ch1 is now Y<br /> In the program, ch1 is first given the value X. Next, ch1 is incremented. This results in<br /> ch1 containing Y, the next character in the ASCII (and Unicode) sequence.<br /> Booleans<br /> Java has a simple type, called boolean, for logical values. It can have only one of two<br /> possible values, true or false. This is the type returned by all relational operators, such<br /> as a < b. boolean is also the type required by the conditional expressions that govern the<br /> control statements such as if and for.<br /> Here is a program that demonstrates the boolean type:</div> <div>632 Java™ 2: The Complete Reference<br /> Applet Architecture<br /> An applet is a window-based program. As such, its architecture is different from the<br /> so-called normal, console-based programs shown in the first part of this book. If you<br /> are familiar with Windows programming, you will be right at home writing applets.<br /> If not, then there are a few key concepts you must understand.<br /> First, applets are event driven. Although we won’t examine event handling until<br /> the following chapter, it is important to understand in a general way how the<br /> event-driven architecture impacts the design of an applet. An applet resembles a set<br /> of interrupt service routines. Here is how the process works. An applet waits until an<br /> event occurs. The AWT notifies the applet about an event by calling an event handler<br /> that has been provided by the applet. Once this happens, the applet must take<br /> appropriate action and then quickly return control to the AWT. This is a crucial point.<br /> For the most part, your applet should not enter a “mode” of operation in which it<br /> maintains control for an extended period. Instead, it must perform specific actions<br /> in response to events and then return control to the AWT run-time system. In those<br /> situations in which your applet needs to perform a repetitive task on its own (for<br /> example, displaying a scrolling message across its window), you must start an<br /> additional thread of execution. (You will see an example later in this chapter.)<br /> Second, the user initiates interaction with an applet—not the other way around. As<br /> you know, in a nonwindowed program, when the program needs input, it will prompt<br /> the user and then call some input method, such as readLine( ). This is not the way it<br /> works in an applet. Instead, the user interacts with the applet as he or she wants, when<br /> he or she wants. These interactions are sent to the applet as events to which the applet<br /> must respond. For example, when the user clicks a mouse inside the applet’s window,<br /> a mouse-clicked event is generated. If the user presses a key while the applet’s window<br /> has input focus, a keypress event is generated. As you will see in later chapters, applets<br /> can contain various controls, such as push buttons and check boxes. When the user<br /> interacts with one of these controls, an event is generated.<br /> While the architecture of an applet is not as easy to understand as that of a<br /> console-based program, Java’s AWT makes it as simple as possible. If you have<br /> written programs for Windows, you know how intimidating that environment can<br /> be. Fortunately, Java’s AWT provides a much cleaner approach that is more<br /> quickly mastered.<br /> An Applet Skeleton<br /> All but the most trivial applets override a set of methods that provides the basic<br /> mechanism by which the browser or applet viewer interfaces to the applet and controls<br /> its execution. Four of these methods—init( ), start( ), stop( ), and destroy( )—are<br /> defined by Applet. Another, paint( ), is defined by the AWT Component class. Default<br /> implementations for all of these methods are provided. Applets do not need to<br /> override those methods they do not use. However, only very simple applets will not</div> <div>774 Java™ 2: The Complete Reference<br /> }<br /> winPan.add(Win98);<br /> winPan.add(winNT);<br /> // Add other OS check boxes to a panel<br /> Panel otherPan = new Panel();<br /> otherPan.add(solaris);<br /> otherPan.add(mac);<br /> // add panels to card deck panel<br /> osCards.add(winPan, "Windows");<br /> osCards.add(otherPan, "Other");<br /> // add cards to main applet panel<br /> add(osCards);<br /> // register to receive action events<br /> Win.addActionListener(this);<br /> Other.addActionListener(this);<br /> // register mouse events<br /> addMouseListener(this);<br /> // Cycle through panels.<br /> public void mousePressed(MouseEvent me) {<br /> cardLO.next(osCards);<br /> }<br /> // Provide empty implementations for the other MouseListener methods.<br /> public void mouseClicked(MouseEvent me) {<br /> }<br /> public void mouseEntered(MouseEvent me) {<br /> }<br /> public void mouseExited(MouseEvent me) {<br /> }<br /> public void mouseReleased(MouseEvent me) {<br /> }<br /> public void actionPerformed(ActionEvent ae) {<br /> if(ae.getSource() == Win) {</div> <div>22 Java™ 2: The Complete Reference<br /> Inheritance interacts with encapsulation as well. If a given class encapsulates some<br /> attributes, then any subclass will have the same attributes plus any that it adds as part<br /> of its specialization (see Figure 2-2). This is a key concept which lets object-oriented<br /> programs grow in complexity linearly rather than geometrically. A new subclass inherits<br /> all of the attributes of all of its ancestors. It does not have unpredictable interactions<br /> with the majority of the rest of the code in the system.<br /> Polymorphism<br /> Polymorphism (from the Greek, meaning “many forms”) is a feature that allows one<br /> interface to be used for a general class of actions. The specific action is determined by<br /> the exact nature of the situation. Consider a stack (which is a last-in, first-out list). You<br /> might have a program that requires three types of stacks. One stack is used for integer<br /> values, one for floating-point values, and one for characters. The algorithm that<br /> implements each stack is the same, even though the data being stored differs. In a non–<br /> object-oriented language, you would be required to create three different sets of stack<br /> routines, with each set using different names. However, because of polymorphism, in<br /> Java you can specify a general set of stack routines that all share the same names.<br /> More generally, the concept of polymorphism is often expressed by the phrase “one<br /> interface, multiple methods.” This means that it is possible to design a generic interface<br /> to a group of related activities. This helps reduce complexity by allowing the same<br /> interface to be used to specify a general class of action. It is the compiler’s job to select the<br /> specific action (that is, method) as it applies to each situation. You, the programmer, do<br /> not need to make this selection manually. You need only remember and utilize the<br /> general interface.</div> <div>THE JAVA LANGUAGE<br /> Chapter 8: Inheritance 215<br /> }<br /> Triangle(double a, double b) {<br /> super(a, b);<br /> }<br /> // override area for right triangle<br /> double area() {<br /> System.out.println("Inside Area for Triangle.");<br /> return dim1 * dim2 / 2;<br /> }<br /> class FindAreas {<br /> public static void main(String args[]) {<br /> Figure f = new Figure(10, 10);<br /> Rectangle r = new Rectangle(9, 5);<br /> Triangle t = new Triangle(10, 8);<br /> Figure figref;<br /> figref = r;<br /> System.out.println("Area is " + figref.area());<br /> figref = t;<br /> System.out.println("Area is " + figref.area());<br /> }<br /> }<br /> figref = f;<br /> System.out.println("Area is " + figref.area());<br /> The output from the program is shown here:<br /> Inside Area for Rectangle.<br /> Area is 45<br /> Inside Area for Triangle.<br /> Area is 40<br /> Area for Figure is undefined.<br /> Area is 0<br /> Through the dual mechanisms of inheritance and run-time polymorphism, it is<br /> possible to define one consistent interface that is used by several different, yet related,</div> <div>36 Java™ 2: The Complete Reference<br /> public static void main(String args[]) {<br /> int x, y;<br /> y = 20;<br /> }<br /> }<br /> // the target of this loop is a block<br /> for(x = 0; x<10; x++) {<br /> System.out.println("This is x: " + x);<br /> System.out.println("This is y: " + y);<br /> y = y - 2;<br /> }<br /> The output generated by this program is shown here:<br /> This is x: 0<br /> This is y: 20<br /> This is x: 1<br /> This is y: 18<br /> This is x: 2<br /> This is y: 16<br /> This is x: 3<br /> This is y: 14<br /> This is x: 4<br /> This is y: 12<br /> This is x: 5<br /> This is y: 10<br /> This is x: 6<br /> This is y: 8<br /> This is x: 7<br /> This is y: 6<br /> This is x: 8<br /> This is y: 4<br /> This is x: 9<br /> This is y: 2<br /> In this case, the target of the for loop is a block of code and not just a single statement.<br /> Thus, each time the loop iterates, the three statements inside the block will be executed.<br /> This fact is, of course, evidenced by the output generated by the program.</div> <div>868 Java™ 2: The Complete Reference<br /> For example, the following program finds tokens that are separated by spaces,<br /> commas, periods, and exclamation points.<br /> // Use split().<br /> import java.util.regex.*;<br /> class RegExpr9 {<br /> public static void main(String args[]) {<br /> // Match lowercase words.<br /> Pattern pat = Pattern.compile("[ ,.!]");<br /> String strs[] = pat.split("one two,alpha9 12!done.");<br /> for(int i=0; i < strs.length; i++)<br /> System.out.println("Next token: " + strs[i]);<br /> }<br /> }<br /> The output is shown here:<br /> Next token: one<br /> Next token: two<br /> Next token: alpha9<br /> Next token: 12<br /> Next token: done<br /> As the output shows, the input sequence is reduced to its individual tokens. Notice that<br /> the delimiters are not included.<br /> Two Pattern-Matching Options<br /> Although the pattern-matching techniques described in the foregoing offer the greatest<br /> flexibility and power, there are two alternatives which you might find useful in some<br /> circumstances. If you only need to perform a one-time pattern match, you can use the<br /> matches( ) method defined by Pattern. It is shown here:<br /> static boolean matches(String pattern, CharSequence str)</div> <div>592 Java™ 2: The Complete Reference<br /> families. TCP is used for reliable stream-based I/O across the network. UDP supports<br /> a simpler, hence faster, point-to-point datagram-oriented model.<br /> The Networking Classes and Interfaces<br /> The classes contained in the java.net package are listed here:<br /> Authenticator (Java 2) InetSocketAddress (Java 2, v1.4) SocketImpl<br /> ContentHandler JarURLConnection (Java 2) SocketPermission<br /> DatagramPacket MulticastSocket URI (Java 2, v1.4)<br /> DatagramSocket NetPermission URL<br /> DatagramSocketImpl NetworkInterface (Java 2, v1.4) URLClassLoader (Java 2)<br /> HttpURLConnection PasswordAuthentication (Java 2) URLConnection<br /> InetAddress ServerSocket URLDecoder (Java 2)<br /> Inet4Address (Java 2, v1.4) Socket URLEncoder<br /> Inet6Address (Java 2, v1.4) SocketAddress (Java 2, v1.4) URLStreamHandler<br /> As you can see, several new classes were added by Java 2, version 1.4. Some of<br /> these are to support the new IPv6 addressing scheme. Others provide some added<br /> flexibility to the original java.net package. Java 2, version 1.4 also added functionality,<br /> such as support for the new I/O classes, to several of the preexisting networking<br /> classes. Most of the additions made by Java 2, version 1.4 are beyond the scope of this<br /> chapter, but three new classes, Inet4Address, Inet6Address, and URI, are briefly<br /> discussed at the end. The java.net package’s interfaces are listed here:<br /> ContentHandlerFactory SocketImplFactory URLStreamHandlerFactory<br /> FileNameMap SocketOptions DatagramSocketImplFactory<br /> (added by Java 2, v1.3)<br /> In the sections that follow, we will examine the main networking classes and show<br /> several examples that apply them.<br /> InetAddress<br /> Whether you are making a phone call, sending mail, or establishing a connection across<br /> the Internet, addresses are fundamental. The InetAddress class is used to encapsulate<br /> both the numerical IP address we discussed earlier and the domain name for that<br /> address. You interact with this class by using the name of an IP host, which is more<br /> convenient and understandable than its IP address. The InetAddress class hides the<br /> number inside. As of Java 2, version 1.4, InetAddress can handle both IPv4 and IPv6<br /> addresses. This discussion assumes IPv4.</div> <div>THE JAVA LIBRARY<br /> Chapter 23: Images 805<br /> The Applet class has an implementation of the imageUpdate( ) method for the<br /> ImageObserver interface that is used to repaint images as they are loaded. You can<br /> override this method in your class to change that behavior.<br /> Here is a simple example of an imageUpdate( ) method:<br /> public boolean imageUpdate(Image img, int flags,<br /> int x, int y, int w, int h) {<br /> if ((flags & ALLBITS) == 0) {<br /> System.out.println("Still processing the image.");<br /> return true;<br /> } else {<br /> System.out.println("Done processing the image.");<br /> return false;<br /> }<br /> }<br /> ImageObserver Example<br /> Now let’s look at a practical example that overrides imageUpdate( ) to make a version of<br /> the SimpleImageLoad applet that doesn’t flicker as much. The default implementation<br /> of imageUpdate( ) in Applet has several problems. First, it repaints the entire image each<br /> time any new data arrives. This causes flashing between the background color and the<br /> image. Second, it uses a feature of Applet.repaint( ) to cause the system to only repaint<br /> the image every tenth of a second or so. This causes a jerky, uneven feel as the image is<br /> painting. Finally, the default implementation knows nothing about images that may fail<br /> to load properly. Many beginning Java programmers are frustrated by the fact that<br /> getImage( ) always succeeds even when the image specified does not exist. You don’t<br /> find out about missing images until imageUpdate( ) occurs. If you use the default<br /> implementation of imageUpdate( ), then you’ll never know what happened. Your<br /> paint( ) method will simply do nothing when you call g.drawImage( ).<br /> The example that follows fixes all three of these problems in ten lines of code. First,<br /> it eliminates the flickering with two small changes. It overrides update( ) so that it calls<br /> paint( ) without painting the background color first. The background is set via<br /> setBackground( ) in init( ), so the initial color is painted just once. Also, it uses a<br /> version of repaint( ) that specifies the rectangle in which to paint. The system will set<br /> the clipping area such that nothing outside of this rectangle is painted. This reduces<br /> repaint flicker and improves performance.<br /> Second, it eliminates the jerky, uneven display of the incoming image by painting<br /> every time it receives an update. These updates occur on a scan line-by-scan line basis,<br /> so an image that is 100 pixels tall will be “repainted” 100 times as it loads. Note that<br /> this is not the fastest way to display an image, just the smoothest.</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 26: A Tour of Swing 943<br /> 1. Create a JTree object.<br /> 2. Create a JScrollPane object. (The arguments to the constructor specify the tree<br /> and the policies for vertical and horizontal scroll bars.)<br /> 3. Add the tree to the scroll pane.<br /> 4. Add the scroll pane to the content pane of the applet.<br /> The following example illustrates how to create a tree and recognize mouse clicks on<br /> it. The init( ) method gets the content pane for the applet. A DefaultMutableTreeNode<br /> object labeled “Options” is created. This is the top node of the tree hierarchy. Additional<br /> tree nodes are then created, and the add( ) method is called to connect these nodes to<br /> the tree. A reference to the top node in the tree is provided as the argument to the<br /> JTree constructor. The tree is then provided as the argument to the JScrollPane<br /> constructor. This scroll pane is then added to the applet. Next, a text field is created<br /> and added to the applet. Information about mouse click events is presented in this text<br /> field. To receive mouse events from the tree, the addMouseListener( ) method of the<br /> JTree object is called. The argument to this method is an anonymous inner class that<br /> extends MouseAdapter and overrides the mouseClicked( ) method.<br /> The doMouseClicked( ) method processes mouse clicks. It calls<br /> getPathForLocation( ) to translate the coordinates of the mouse click into a TreePath<br /> object. If the mouse is clicked at a point that does not cause a node selection, the return<br /> value from this method is null. Otherwise, the tree path can be converted to a string<br /> and presented in the text field.<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import javax.swing.*;<br /> import javax.swing.tree.*;<br /> /*<br /> <applet code="JTreeEvents" width=400 height=200><br /> </applet><br /> */<br /> public class JTreeEvents extends JApplet {<br /> JTree tree;<br /> JTextField jtf;<br /> public void init() {</div> <div>THE JAVA LIBRARY<br /> Chapter 22: Using AWT Controls, Layout Managers, and Menus 791<br /> The eventMask argument is a bit mask that defines the events to be delivered to this<br /> component. The AWTEvent class defines int constants for making this mask. Several<br /> are shown here:<br /> ACTION_EVENT_MASK<br /> ADJUSTMENT_EVENT_MASK<br /> COMPONENT_EVENT_MASK<br /> CONTAINER_EVENT_MASK<br /> FOCUS_EVENT_MASK<br /> INPUT_METHOD_EVENT_MASK<br /> ITEM_EVENT_MASK<br /> KEY_EVENT_MASK<br /> MOUSE_EVENT_MASK<br /> MOUSE_MOTION_EVENT_MASK<br /> MOUSE_WHEEL_EVENT_MASK<br /> TEXT_EVENT_MASK<br /> WINDOW_EVENT_MASK<br /> You must also override the appropriate method from one of your superclasses in<br /> order to process the event. Table 22-1 lists the methods most commonly used and the<br /> classes that provide them.<br /> The following sections provide simple programs that show how to extend several<br /> AWT components.<br /> Class<br /> Processing Methods<br /> Button processActionEvent( )<br /> Checkbox processItemEvent( )<br /> CheckboxMenuItem processItemEvent( )<br /> Choice processItemEvent( )<br /> Component processComponentEvent( ), processFocusEvent( ),<br /> processKeyEvent( ), processMouseEvent( ),<br /> processMouseMotionEvent( ), processMouseWheelEvent ( )<br /> List processActionEvent( ), processItemEvent( )<br /> MenuItem processActionEvent( )<br /> Scrollbar processAdjustmentEvent( )<br /> TextComponent processTextEvent( )<br /> Table 22-1.<br /> Event Processing Methods</div> <div>THE JAVA LIBRARY<br /> Chapter 13: String Handling 373<br /> immutable. Thankfully, Java hides most of the complexity of conversion between<br /> Strings and StringBuffers. Actually, many programmers will never feel the need to<br /> use StringBuffer directly and will be able to express most operations in terms of the<br /> + operator on String variables.<br /> insert( )<br /> The insert( ) method inserts one string into another. It is overloaded to accept values of<br /> all the simple types, plus Strings and Objects. Like append( ), it calls String.valueOf( )<br /> to obtain the string representation of the value it is called with. This string is then<br /> inserted into the invoking StringBuffer object. These are a few of its forms:<br /> StringBuffer insert(int index, String str)<br /> StringBuffer insert(int index, char ch)<br /> StringBuffer insert(int index, Object obj)<br /> Here, index specifies the index at which point the string will be inserted into the<br /> invoking StringBuffer object.<br /> The following sample program inserts “like” between “I” and “Java”:<br /> // Demonstrate insert().<br /> class insertDemo {<br /> public static void main(String args[]) {<br /> StringBuffer sb = new StringBuffer("I Java!");<br /> }<br /> }<br /> sb.insert(2, "like ");<br /> System.out.println(sb);<br /> The output of this example is shown here:<br /> I like Java!<br /> reverse( )<br /> You can reverse the characters within a StringBuffer object using reverse( ), shown here:<br /> StringBuffer reverse( )<br /> This method returns the reversed object on which it was called. The following program<br /> demonstrates reverse( ):<br /> // Using reverse() to reverse a StringBuffer.<br /> class ReverseDemo {</div> <div>THE JAVA LIBRARY<br /> Chapter 21: Introducing the AWT: Working with Windows, Graphics, and Text 717<br /> }<br /> }<br /> g.drawLine(chsX, chsY-10, chsX, chsY+10);<br /> g.setPaintMode();<br /> Sample output from this program is shown here:<br /> Working with Fonts<br /> The AWT supports multiple type fonts. Fonts have emerged from the domain of<br /> traditional typesetting to become an important part of computer-generated documents<br /> and displays. The AWT provides flexibility by abstracting font-manipulation<br /> operations and allowing for dynamic selection of fonts.<br /> Beginning with Java 2, fonts have a family name, a logical font name, and a face<br /> name. The family name is the general name of the font, such as Courier. The logical name<br /> specifies a category of font, such as Monospaced. The face name specifies a specific font,<br /> such as Courier Italic.<br /> Fonts are encapsulated by the Font class. Several of the methods defined by Font<br /> are listed in Table 21-2.<br /> The Font class defines these variables:<br /> Variable<br /> String name<br /> float pointSize<br /> int size<br /> int style<br /> Meaning<br /> Name of the font<br /> Size of the font in points<br /> Size of the font in points<br /> Font style</div> <div>APPLYING JAVA<br /> Chapter 32: Scrabblet: A Multiplayer Word Game 1127<br /> ClientConnection.java<br /> This class is the mirror image of ServerConnection in the applet. One of these is<br /> created for each client. Its job is to manage all of the I/O to and from a client. The<br /> private instance variables hold all of the states about this client. The Socket is stored in<br /> sock. The buffered reader and output streams are stored in in and out. The host name<br /> of the client machine is kept in host. A reference to the Server instance that created this<br /> client is held in server. The name of the player on this client is stored in name, while<br /> the player’s automatically assigned ID number is held in id. The busy Boolean variable<br /> stores whether or not this client is actively engaged in a game.<br /> import java.net.*;<br /> import java.io.*;<br /> import java.util.*;<br /> class ClientConnection implements Runnable {<br /> private Socket sock;<br /> private BufferedReader in;<br /> private OutputStream out;<br /> private String host;<br /> private Server server;<br /> private static final String CRLF = "\r\n";<br /> private String name = null; // for humans<br /> private String id;<br /> private boolean busy = false;<br /> ClientConnection( )<br /> The constructor saves the reference to the server and socket and remembers the unique<br /> ID. We wrap an InputStreamReader and a BufferedReader around the input so that it<br /> can call readLine( ) on it. Then it writes the id back to the client to let it know what<br /> number it is. Finally, it creates and starts a new Thread to handle this connection.<br /> public ClientConnection(Server srv, Socket s, int i) {<br /> try {<br /> server = srv;<br /> sock = s;<br /> in = new BufferedReader(new<br /> InputStreamReader(s.getInputStream()));</div> <div>526 Java™ 2: The Complete Reference<br /> // Demonstrate random Gaussian values.<br /> import java.util.Random;<br /> class RandDemo {<br /> public static void main(String args[]) {<br /> Random r = new Random();<br /> double val;<br /> double sum = 0;<br /> int bell[] = new int[10];<br /> for(int i=0; i<100; i++) {<br /> val = r.nextGaussian();<br /> sum += val;<br /> double t = -2;<br /> for(int x=0; x<10; x++, t += 0.5)<br /> if(val < t) {<br /> bell[x]++;<br /> break;<br /> }<br /> }<br /> System.out.println("Average of values: " +<br /> (sum/100));<br /> }<br /> }<br /> // display bell curve, sideways<br /> for(int i=0; i<10; i++) {<br /> for(int x=bell[i]; x>0; x--)<br /> System.out.print("*");<br /> System.out.println();<br /> }<br /> Here is a sample program run. As you can see, a bell-like distribution of numbers<br /> is obtained.<br /> Average of values: 0.0702235271133344<br /> **<br /> *******<br /> ******<br /> ***************<br /> ******************<br /> *****************<br /> *************<br /> **********<br /> ********<br /> ***</div> <div>1086 Java™ 2: The Complete Reference<br /> }<br /> }<br /> Letter l = bag.takeOut();<br /> board.addLetter(l);<br /> private void theypick() {<br /> for (int i = 0; i < 7; i++) {<br /> Letter l = bag.takeOut();<br /> theirs[i] = l;<br /> }<br /> }<br /> start_Game( )<br /> In single-player mode, start_Game( ) pops up the splash screen in a Frame window.<br /> It then creates a playing board, passing in no parameters to the constructor, which<br /> indicates single-player mode.<br /> In head-to-head mode, we remove the selection list components and add the chat<br /> window to the applet. We then add the board and Done button to the applet. Next, we<br /> create the bag, and if it is ourturn, wepick( ) is first, then theypick( ). In the case where<br /> we don’t have the first turn, we disable the board and the Done button, and theypick( )<br /> is first. We then force the board to repaint, which initializes it.<br /> private void start_Game(int seed) {<br /> if (single) {<br /> Frame popup = new Frame("Scrabblet");<br /> popup.setSize(400, 300);<br /> popup.add("Center", ican);<br /> popup.setResizable(false);<br /> popup.show();<br /> board = new Board();<br /> showStatus("no server found, playing solo");<br /> ourturn = true;<br /> } else {<br /> remove(idList);<br /> remove(challenge);<br /> board = new Board(name, others_name);<br /> chat = new TextField();<br /> chat.addActionListener(this);<br /> add("North", chat);</div> <div>THE JAVA LIBRARY<br /> Chapter 17: Input/Output: Exploring java.io 557<br /> }<br /> }<br /> case ' ':<br /> if (marked) {<br /> marked = false;<br /> f.reset();<br /> System.out.print("&");<br /> } else<br /> System.out.print((char) c);<br /> break;<br /> default:<br /> if (!marked)<br /> System.out.print((char) c);<br /> break;<br /> }<br /> }<br /> Notice that this example uses mark(32), which preserves the mark for the next 32 bytes<br /> read (which is enough for all entity references). Here is the output produced by this<br /> program:<br /> This is a (c) copyright symbol but this is © not.<br /> Use of mark( ) is restricted to access within the buffer. This means that you can only<br /> specify a parameter to mark( ) that is smaller than the buffer size of the stream.<br /> BufferedOutputStream<br /> A BufferedOutputStream is similar to any OutputStream with the exception of an<br /> added flush( ) method that is used to ensure that data buffers are physically written to<br /> the actual output device. Since the point of a BufferedOutputStream is to improve<br /> performance by reducing the number of times the system actually writes data, you may<br /> need to call flush( ) to cause any data that is in the buffer to get written.<br /> Unlike buffered input, buffering output does not provide additional functionality.<br /> Buffers for output in Java are there to increase performance. Here are the two available<br /> constructors:<br /> BufferedOutputStream(OutputStream outputStream)<br /> BufferedOutputStream(OutputStream outputStream, int bufSize)<br /> The first form creates a buffered stream using a buffer of 512 bytes. In the second form,<br /> the size of the buffer is passed in bufSize.</div> <div>Chapter 5<br /> Control Statements<br /> 99</div> <div>Contents<br /> xv<br /> Storing User-Defined Classes in Collections . . . . . . . . . . . . . . . . . . . . . . . . . 460<br /> The RandomAccess Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462<br /> Working with Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462<br /> The Map Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462<br /> The Map Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466<br /> Comparators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471<br /> Using a Comparator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472<br /> The Collection Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475<br /> Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 480<br /> The Legacy Classes and Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484<br /> The Enumeration Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484<br /> Vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485<br /> Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490<br /> Dictionary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492<br /> Hashtable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494<br /> Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 498<br /> Using store( ) and load( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502<br /> Collections Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504<br /> 16 java.util Part 2: More Utility Classes . . . . . . . . . . . . . . . . . . . . 505<br /> StringTokenizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506<br /> BitSet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508<br /> Date . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 512<br /> Date Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514<br /> Calendar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514<br /> GregorianCalendar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519<br /> TimeZone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521<br /> SimpleTimeZone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522<br /> Locale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 523<br /> Random . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524<br /> Observable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 527<br /> The Observer Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 528<br /> An Observer Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 528<br /> Timer and TimerTask . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 531<br /> Currency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534<br /> The java.util.zip Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536<br /> The java.util.jar Package . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536<br /> 17 Input/Output: Exploring java.io . . . . . . . . . . . . . . . . . . . . . . . 537<br /> The Java I/O Classes and Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 538<br /> File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 539<br /> Directories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 542<br /> Using FilenameFilter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 543<br /> The listFiles( ) Alternative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 544<br /> Creating Directories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545<br /> The Stream Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545<br /> The Byte Streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 546</div> <div>THE JAVA LIBRARY<br /> Chapter 23: Images 825<br /> /*<br /> * <applet code=ImageFilterDemo width=350 height=450><br /> * <param name=img value=vincent.jpg><br /> * <param name=filters value="Grayscale+Invert+Contrast+Blur+ Sharpen"><br /> * </applet><br /> */<br /> import java.applet.*;<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import java.util.*;<br /> public class ImageFilterDemo extends Applet implements ActionListener {<br /> Image img;<br /> PlugInFilter pif;<br /> Image fimg;<br /> Image curImg;<br /> LoadedImage lim;<br /> Label lab;<br /> Button reset;<br /> public void init() {<br /> setLayout(new BorderLayout());<br /> Panel p = new Panel();<br /> add(p, BorderLayout.SOUTH);<br /> reset = new Button("Reset");<br /> reset.addActionListener(this);<br /> p.add(reset);<br /> StringTokenizer st = new StringTokenizer(getParameter("filters"), "+");<br /> while(st.hasMoreTokens()) {<br /> Button b = new Button(st.nextToken());<br /> b.addActionListener(this);<br /> p.add(b);<br /> }<br /> lab = new Label("");<br /> add(lab, BorderLayout.NORTH);<br /> img = getImage(getDocumentBase(), getParameter("img"));<br /> lim = new LoadedImage(img);</div> <div>488 Java™ 2: The Complete Reference<br /> Method<br /> int size( )<br /> String toString( )<br /> void trimToSize( )<br /> Description<br /> Returns the number of elements<br /> currently in the vector.<br /> Returns the string equivalent of<br /> the vector.<br /> Sets the vector’s capacity equal to<br /> the number of elements that it<br /> currently holds.<br /> Table 15-10.<br /> The Methods Defined by Vector (continued)<br /> Because Vector implements List, you can use a vector just like you use an ArrayList<br /> instance. You can also manipulate one using its legacy methods. For example, after you<br /> instantiate a Vector, you can add an element to it by calling addElement( ). To obtain<br /> the element at a specific location, call elementAt( ). To obtain the first element in the<br /> vector, call firstElement( ). To retrieve the last element, call lastElement( ). You can<br /> obtain the index of an element by using indexOf( ) and lastIndexOf( ). To remove an<br /> element, call removeElement( ) or removeElementAt( ).<br /> The following program uses a vector to store various types of numeric objects. It<br /> demonstrates several of the legacy methods defined by Vector. It also demonstrates the<br /> Enumeration interface.<br /> // Demonstrate various Vector operations.<br /> import java.util.*;<br /> class VectorDemo {<br /> public static void main(String args[]) {<br /> // initial size is 3, increment is 2<br /> Vector v = new Vector(3, 2);<br /> System.out.println("Initial size: " + v.size());<br /> System.out.println("Initial capacity: " +<br /> v.capacity());</div> <div>1030 Java™ 2: The Complete Reference<br /> createRandomArray( )<br /> The createRandomArray( ) static method creates the two-dimensional random array.<br /> It takes two parameters that describe the size of the applet. It is highly optimized,<br /> because originally it was too slow. It includes its own random-number generator that is<br /> very fast, but with a short cycle. Because of this, it is fairly complicated and beyond the<br /> scope of this book. The basic idea is that Java’s built-in random-number generator is<br /> better at generating truly random distribution, but it is too slow for this application.<br /> Plus, the user will not notice exactly how random this transition is, so Robert’s<br /> home-grown random-number generator is sufficient.<br /> init( )<br /> The init( ) method for this transition starts like all other transitions, with a call to the<br /> base class’ init( ) method. Then, like some other transitions, it copies all of the old<br /> billboard’s pixels into the work_pixels array.<br /> The two-dimensional random array is pulled out of the object_table for an applet<br /> of this size. If it does not exist yet, it is created and stored in the object_table. With the<br /> random array in hand, the method just loops through each cell and each index in the<br /> random array, copying pixels from the next billboard into the work pixels.<br /> The Code<br /> Here is the source code for the FadeTransition class:<br /> import java.awt.*;<br /> import java.awt.image.*;<br /> public class FadeTransition extends BillTransition {<br /> private static final int CELLS = 7;<br /> private static final int MULTIPLIER = 0x5D1E2F;<br /> private static short[][] createRandomArray(int number_pixels,<br /> int cell_h) {<br /> int total_cells = CELLS + 1;<br /> int new_pixels_per_cell = number_pixels / total_cells;<br /> short[][] random = new short[total_cells][new_pixels_per_cell];<br /> int random_count[] = new int[total_cells];<br /> for(int s = 0; s < total_cells; ++s) {<br /> random_count[s] = 0;<br /> }<br /> int cell;<br /> int rounded_new_pixels_per_cell =<br /> new_pixels_per_cell * total_cells;</div> <div>354 Java™ 2: The Complete Reference<br /> By overriding toString( ) for classes that you create, you allow them to be fully<br /> integrated into Java’s programming environment. For example, they can be used in<br /> print( ) and println( ) statements and in concatenation expressions. The following<br /> program demonstrates this by overriding toString( ) for the Box class:<br /> // Override toString() for Box class.<br /> class Box {<br /> double width;<br /> double height;<br /> double depth;<br /> }<br /> Box(double w, double h, double d) {<br /> width = w;<br /> height = h;<br /> depth = d;<br /> }<br /> public String toString() {<br /> return "Dimensions are " + width + " by " +<br /> depth + " by " + height + ".";<br /> }<br /> class toStringDemo {<br /> public static void main(String args[]) {<br /> Box b = new Box(10, 12, 14);<br /> String s = "Box b: " + b; // concatenate Box object<br /> }<br /> }<br /> System.out.println(b); // convert Box to string<br /> System.out.println(s);<br /> The output of this program is shown here:<br /> Dimensions are 10.0 by 14.0 by 12.0<br /> Box b: Dimensions are 10.0 by 14.0 by 12.0<br /> As you can see, Box’s toString( ) method is automatically invoked when a Box<br /> object is used in a concatenation expression or in a call to println( ).</div> <div>148 Java™ 2: The Complete Reference<br /> }<br /> // This is the constructor for Box.<br /> Box(double w, double h, double d) {<br /> width = w;<br /> height = h;<br /> depth = d;<br /> }<br /> // compute and return volume<br /> double volume() {<br /> return width * height * depth;<br /> }<br /> class BoxDemo7 {<br /> public static void main(String args[]) {<br /> // declare, allocate, and initialize Box objects<br /> Box mybox1 = new Box(10, 20, 15);<br /> Box mybox2 = new Box(3, 6, 9);<br /> double vol;<br /> // get volume of first box<br /> vol = mybox1.volume();<br /> System.out.println("Volume is " + vol);<br /> }<br /> }<br /> // get volume of second box<br /> vol = mybox2.volume();<br /> System.out.println("Volume is " + vol);<br /> The output from this program is shown here:<br /> Volume is 3000.0<br /> Volume is 162.0<br /> As you can see, each object is initialized as specified in the parameters to its<br /> constructor. For example, in the following line,</div> <div>THE JAVA LIBRARY<br /> Chapter 14: Exploring java.lang 417<br /> Method<br /> Field[ ] getFields( )<br /> throws SecurityException<br /> Class[ ] getInterfaces( )<br /> Method[ ] getMethods( )<br /> throws SecurityException<br /> String getName( )<br /> ProtectionDomain getProtectionDomain( )<br /> Class getSuperclass( )<br /> boolean isInterface( )<br /> Object newInstance( )<br /> throws IllegalAccessException,<br /> InstantiationException<br /> String toString( )<br /> Description<br /> Returns a Field object for all the<br /> public fields of this class.<br /> When invoked on an object, this<br /> method returns an array of the<br /> interfaces implemented by the class<br /> type of the object. When invoked on<br /> an interface, this method returns<br /> an array of interfaces extended by<br /> the interface.<br /> Returns a Method object for all the<br /> public methods of this class.<br /> Returns the complete name<br /> of the class or interface of the<br /> invoking object.<br /> Returns the protection domain<br /> associated with the invoking object.<br /> (Added by Java 2)<br /> Returns the superclass of the<br /> invoking object. The return value<br /> is null if the invoking object is of<br /> type Object.<br /> Returns true if the invoking object<br /> is an interface. Otherwise, it<br /> returns false.<br /> Creates a new instance (i.e., a new<br /> object) that is of the same type as<br /> the invoking object. This is<br /> equivalent to using new with the<br /> class’ default constructor. The new<br /> object is returned.<br /> Returns the string representation of<br /> the invoking object or interface.<br /> Table 14-13.<br /> Some Methods Defined by Class (continued)</div> <div>626 Java™ 2: The Complete Reference<br /> }<br /> }<br /> }<br /> ds = new DatagramSocket(clientPort);<br /> TheClient();<br /> This sample program is restricted by the DatagramSocket constructor to running<br /> between two ports on the local machine. To use the program, run<br /> java WriteServer<br /> in one window; this will be the client. Then run<br /> java WriteServer 1<br /> This will be the server. Anything that is typed in the server window will be sent to the<br /> client window after a newline is received.<br /> This example requires that your computer be connected to the Internet.<br /> Inet4Address and Inet6Address<br /> As mentioned at the start of this chapter, Java 2, version 1.4 added support for IPv6<br /> addresses. Because of this, two new subclasses of InetAddress were created:<br /> Inet4Address and Inet6Address. Inet4Address represents a traditional style, IPv4<br /> address. Inet6Address encapsulates a new-style IPv6 address. Because they are<br /> subclasses of InetAddress, an InetAddress reference can refer to either. This is one<br /> way that Java was able to add IPv6 functionality without breaking existing code or<br /> adding many more classes. For the most part, you can simply use InetAddress when<br /> working with IP addresses because it can accommodate both styles.<br /> The URI Class<br /> Java 2, version 1.4 added the URI class, which encapsulates a Uniform Resource<br /> Identifier. URIs are similar to URLs. In fact, URLs constitute a subset of URIs. A URI<br /> represents a standard way to identify a resource. A URL also describes how to<br /> access the resource.</div> <div>THE JAVA LIBRARY<br /> Chapter 16: java.util Part 2: More Utility Classes 535<br /> c = Currency.getInstance(Locale.US);<br /> }<br /> }<br /> System.out.println("Symbol: " + c.getSymbol());<br /> System.out.println("Default fractional digits: " +<br /> c.getDefaultFractionDigits());<br /> The output is shown here.<br /> Symbol: $<br /> Default fractional digits: 2<br /> Method<br /> Description<br /> String getCurrencyCode( ) Returns the code (as defined by ISO 4217)<br /> that describes the invoking currency.<br /> int getDefaultFractionDigits( )<br /> static Currency<br /> getInstance(Locale localeObj)<br /> static Currency<br /> getInstance(String code)<br /> Returns the number of digits after the<br /> decimal point that are normally used by<br /> the invoking currency. For example, there<br /> are 2 fractional digits normally used for<br /> dollars.<br /> Returns a Currency object for the locale<br /> specified by localeObj.<br /> Returns a Currency object associated<br /> with the currency code passed in code.<br /> String getSymbol( ) Returns the currency symbol (such as $)<br /> for the invoking object.<br /> String getSymbol(Locale localeObj) Returns the currency symbol (such as $)<br /> for the locale passed in localeObj.<br /> String toString( )<br /> Returns the currency code for the<br /> invoking object.<br /> Table 16-10.<br /> The Methods Defined by Currency</div> <div>926 Java™ 2: The Complete Reference<br /> of its subclasses is JTextField, which allows you to edit one line of text. Some of its<br /> constructors are shown here:<br /> JTextField( )<br /> JTextField(int cols)<br /> JTextField(String s, int cols)<br /> JTextField(String s)<br /> Here, s is the string to be presented, and cols is the number of columns in the text field.<br /> The following example illustrates how to create a text field. The applet begins by<br /> getting its content pane, and then a flow layout is assigned as its layout manager. Next,<br /> a JTextField object is created and is added to the content pane.<br /> import java.awt.*;<br /> import javax.swing.*;<br /> /*<br /> <applet code="JTextFieldDemo" width=300 height=50><br /> </applet><br /> */<br /> public class JTextFieldDemo extends JApplet {<br /> JTextField jtf;<br /> public void init() {<br /> // Get content pane<br /> Container contentPane = getContentPane();<br /> contentPane.setLayout(new FlowLayout());<br /> }<br /> }<br /> // Add text field to content pane<br /> jtf = new JTextField(15);<br /> contentPane.add(jtf);<br /> Output from this applet is shown here:</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 26: A Tour of Swing 945<br /> // Add text field to applet<br /> jtf = new JTextField("", 20);<br /> contentPane.add(jtf, BorderLayout.SOUTH);<br /> // Anonymous inner class to handle mouse clicks<br /> tree.addMouseListener(new MouseAdapter() {<br /> public void mouseClicked(MouseEvent me) {<br /> doMouseClicked(me);<br /> }<br /> });<br /> }<br /> void doMouseClicked(MouseEvent me) {<br /> TreePath tp = tree.getPathForLocation(me.getX(), me.getY());<br /> if(tp != null)<br /> jtf.setText(tp.toString());<br /> else<br /> jtf.setText("");<br /> }<br /> }<br /> Output from this applet is shown here:</div> <div>528 Java™ 2: The Complete Reference<br /> Notice that notifyObservers( ) has two forms: one that takes an argument and<br /> one that does not. If you call notifyObservers( ) with an argument, this object is<br /> passed to the observer’s update( ) method as its second parameter. Otherwise, null<br /> is passed to update( ). You can use the second parameter for passing any type of<br /> object that is appropriate for your application.<br /> The Observer Interface<br /> To observe an observable object, you must implement the Observer interface.<br /> This interface defines only the one method shown here:<br /> void update(Observable observOb, Object arg)<br /> Here, observOb is the object being observed, and arg is the value passed by<br /> notifyObservers( ). The update( ) method is called when a change in the<br /> observed object takes place.<br /> An Observer Example<br /> Here is an example that demonstrates an observable object. It creates an observer class,<br /> called Watcher, that implements the Observer interface. The class being monitored is<br /> called BeingWatched. It extends Observable. Inside BeingWatched is the method<br /> counter( ), which simply counts down from a specified value. It uses sleep( ) to wait a<br /> tenth of a second between counts. Each time the count changes, notifyObservers( ) is<br /> called with the current count passed as its argument. This causes the update( ) method<br /> inside Watcher to be called, which displays the current count. Inside main( ), a<br /> Watcher and a BeingWatched object, called observing and observed, respectively, are<br /> created. Then, observing is added to the list of observers for observed. This means that<br /> observing.update( ) will be called each time counter( ) calls notifyObservers( ).<br /> /* Demonstrate the Observable class and the<br /> Observer interface.<br /> */<br /> import java.util.*;<br /> // This is the observing class.<br /> class Watcher implements Observer {<br /> public void update(Observable obj, Object arg) {<br /> System.out.println("update() called, count is " +<br /> ((Integer)arg).intValue());<br /> }<br /> }</div> <div>Chapter 31<br /> The Lavatron Applet:<br /> A Sports Arena Display<br /> 1057</div> <div>270 Java™ 2: The Complete Reference<br /> In the first form, causeExc is the exception that causes the current exception. That is,<br /> causeExc is the underlying reason that an exception occurred. The second form allows<br /> you to specify a description at the same time that you specify a cause exception. These<br /> two constructors have also been added to the Error, Exception, and RuntimeException<br /> classes.<br /> The chained exception methods added to Throwable are getCause( ) and initCause( ).<br /> These methods are shown in Table 10-3, and are repeated here for the sake of discussion.<br /> Throwable getCause( )<br /> Throwable initCause(Throwable causeExc)<br /> The getCause( ) method returns the exception that underlies the current exception.<br /> If there is no underlying exception, null is returned. The initCause( ) method associates<br /> causeExc with the invoking exception and returns a reference to the exception. Thus, you<br /> can associate a cause with an exception after the exception has been created. However, the<br /> cause exception can be set only once. Thus, you can call initCause( ) only once for each<br /> exception object. Furthermore, if the cause exception was set by a constructor, then you<br /> can’t set it again using initCause( ).<br /> In general, initCause( ) is used to set a cause for legacy exception classes which<br /> don’t support the two additional constructors described earlier. At the time of this<br /> writing, most of Java’s built-in exceptions, such as ArithmeticException, do not define<br /> the additional constructors. Thus, you will use initCause( ) if you need to add an<br /> exception chain to these exceptions. When creating your own exception classes you<br /> will want to add the two chained-exception constructors if you will be using your<br /> exceptions in situations in which layered exceptions are possible.<br /> Here is an example that illustrates the mechanics of handling chained exceptions.<br /> // Demonstrate exception chaining.<br /> class ChainExcDemo {<br /> static void demoproc() {<br /> // create an exception<br /> NullPointerException e =<br /> new NullPointerException("top layer");<br /> // add a cause<br /> e.initCause(new ArithmeticException("cause"));<br /> }<br /> throw e;<br /> public static void main(String args[]) {<br /> try {<br /> demoproc();</div> <div>APPLYING JAVA<br /> Chapter 32: Scrabblet: A Multiplayer Word Game 1095<br /> }<br /> vertical = atplay[1].x == x;<br /> if (!horizontal && !vertical) // diagonal...<br /> return null;<br /> for (int i = 2; i < ntiles; i++) {<br /> if (horizontal && atplay[i].y != y<br /> || vertical && atplay[i].x != x)<br /> return null;<br /> }<br /> Next, it looks at each tile to be sure that at least one of them is touching an existing<br /> tile on one of its four sides. A special case is made for the beginning of the game: if the<br /> center tile is covered and more than one tile is played, it is legal.<br /> // make sure that at least one played tile is<br /> // touching at least one existing tile.<br /> boolean attached = false;<br /> for (int i = 0; i < ntiles; i++) {<br /> Point p = atplay[i].recall();<br /> int x = p.x;<br /> int y = p.y;<br /> if ((x == 7 && y == 7 && ntiles > 1) ||<br /> existingLetterAt(x-1, y) || existingLetterAt(x+1, y) ||<br /> existingLetterAt(x, y-1) || existingLetterAt(x, y+1)) {<br /> attached = true;<br /> break;<br /> }<br /> }<br /> if (!attached) {<br /> return null;<br /> }<br /> This next loop iterates over every letter in the main word, (i == –1), then comes<br /> back again for each letter (i == 0..ntiles), which might also create a word orthogonal to<br /> the main direction, which is managed via horizontal.<br /> // we use -1 to mean check the major direction first<br /> // then 0..ntiles checks for words orthogonal to it.<br /> for (int i = -1; i < ntiles; i++) {<br /> Point p = atplay[i==-1?0:i].recall(); // where is it?</div> <div>THE JAVA LANGUAGE<br /> Chapter 8: Inheritance 203<br /> This program displays the following:<br /> i in superclass: 1<br /> i in subclass: 2<br /> Although the instance variable i in B hides the i in A, super allows access to the i<br /> defined in the superclass. As you will see, super can also be used to call methods that<br /> are hidden by a subclass.<br /> Creating a Multilevel Hierarchy<br /> Up to this point, we have been using simple class hierarchies that consist of only a<br /> superclass and a subclass. However, you can build hierarchies that contain as many<br /> layers of inheritance as you like. As mentioned, it is perfectly acceptable to use a<br /> subclass as a superclass of another. For example, given three classes called A, B,<br /> and C, C can be a subclass of B, which is a subclass of A. When this type of situation<br /> occurs, each subclass inherits all of the traits found in all of its superclasses. In this<br /> case, C inherits all aspects of B and A. To see how a multilevel hierarchy can be useful,<br /> consider the following program. In it, the subclass BoxWeight is used as a superclass to<br /> create the subclass called Shipment. Shipment inherits all of the traits of BoxWeight<br /> and Box, and adds a field called cost, which holds the cost of shipping such a parcel.<br /> // Extend BoxWeight to include shipping costs.<br /> // Start with Box.<br /> class Box {<br /> private double width;<br /> private double height;<br /> private double depth;<br /> // construct clone of an object<br /> Box(Box ob) { // pass object to constructor<br /> width = ob.width;<br /> height = ob.height;<br /> depth = ob.depth;<br /> }<br /> // constructor used when all dimensions specified<br /> Box(double w, double h, double d) {<br /> width = w;<br /> height = h;</div> <div>244 Java™ 2: The Complete Reference<br /> constant variables into the class name space as final variables. The next example uses<br /> this technique to implement an automated “decision maker”:<br /> import java.util.Random;<br /> interface SharedConstants {<br /> int NO = 0;<br /> int YES = 1;<br /> int MAYBE = 2;<br /> int LATER = 3;<br /> int SOON = 4;<br /> int NEVER = 5;<br /> }<br /> class Question implements SharedConstants {<br /> Random rand = new Random();<br /> int ask() {<br /> int prob = (int) (100 * rand.nextDouble());<br /> if (prob < 30)<br /> return NO; // 30%<br /> else if (prob < 60)<br /> return YES; // 30%<br /> else if (prob < 75)<br /> return LATER; // 15%<br /> else if (prob < 98)<br /> return SOON; // 13%<br /> }<br /> }<br /> else<br /> return NEVER; // 2%<br /> class AskMe implements SharedConstants {<br /> static void answer(int result) {<br /> switch(result) {<br /> case NO:<br /> System.out.println("No");<br /> break;<br /> case YES:<br /> System.out.println("Yes");</div> <div>THE JAVA LIBRARY<br /> Chapter 24: New I/O, Regular Expressions, and Other Packages 879<br /> The argument is a Date object that is to be displayed. The method returns a string<br /> containing the formatted information.<br /> The following listing illustrates how to format date information. It begins by<br /> creating a Date object. This captures the current date and time information. Then it<br /> outputs the date information by using different styles and locales.<br /> // Demonstrate date formats.<br /> import java.text.*;<br /> import java.util.*;<br /> public class DateFormatDemo {<br /> public static void main(String args[]) {<br /> Date date = new Date();<br /> DateFormat df;<br /> df = DateFormat.getDateInstance(DateFormat.SHORT, Locale.JAPAN);<br /> System.out.println("Japan: " + df.format(date));<br /> df = DateFormat.getDateInstance(DateFormat.MEDIUM, Locale.KOREA);<br /> System.out.println("Korea: " + df.format(date));<br /> df = DateFormat.getDateInstance(DateFormat.LONG, Locale.UK);<br /> System.out.println("United Kingdom: " + df.format(date));<br /> }<br /> }<br /> df = DateFormat.getDateInstance(DateFormat.FULL, Locale.US);<br /> System.out.println("United States: " + df.format(date));<br /> Sample output from this program is shown here:<br /> Japan: 02/05/08<br /> Korea: 2002-05-08<br /> United Kingdom: 08 May 2002<br /> United States: Wednesday, May 8, 2002<br /> The getTimeInstance( ) method returns an instance of DateFormat that can format<br /> time information. It is available in these versions:<br /> static final DateFormat getTimeInstance( )<br /> static final DateFormat getTimeInstance(int style)<br /> static final DateFormat getTimeInstance(int style, Locale locale)</div> <div>264 Java™ 2: The Complete Reference<br /> System.out.println("procB's finally");<br /> }<br /> }<br /> // Execute a try block normally.<br /> static void procC() {<br /> try {<br /> System.out.println("inside procC");<br /> } finally {<br /> System.out.println("procC's finally");<br /> }<br /> }<br /> }<br /> public static void main(String args[]) {<br /> try {<br /> procA();<br /> } catch (Exception e) {<br /> System.out.println("Exception caught");<br /> }<br /> procB();<br /> procC();<br /> }<br /> In this example, procA( ) prematurely breaks out of the try by throwing an<br /> exception. The finally clause is executed on the way out. procB( )’s try statement is<br /> exited via a return statement. The finally clause is executed before procB( ) returns. In<br /> procC( ), the try statement executes normally, without error. However, the finally<br /> block is still executed.<br /> If a finally block is associated with a try, the finally block will be executed upon<br /> conclusion of the try.<br /> Here is the output generated by the preceding program:<br /> inside procA<br /> procA’s finally<br /> Exception caught<br /> inside procB<br /> procB’s finally<br /> inside procC<br /> procC’s finally</div> <div>THE JAVA LANGUAGE<br /> Chapter 4: Operators 87<br /> Each time you shift a value to the right, it divides that value by two—and discards<br /> any remainder. You can take advantage of this for high-performance integer division<br /> by 2. Of course, you must be sure that you are not shifting any bits off the right end.<br /> When you are shifting right, the top (leftmost) bits exposed by the right shift are<br /> filled in with the previous contents of the top bit. This is called sign extension and serves<br /> to preserve the sign of negative numbers when you shift them right. For example, –8<br /> >> 1 is –4, which, in binary, is<br /> 11111000 –8<br /> >>1<br /> 11111100 –4<br /> It is interesting to note that if you shift –1 right, the result always remains –1, since<br /> sign extension keeps bringing in more ones in the high-order bits.<br /> Sometimes it is not desirable to sign-extend values when you are shifting them to<br /> the right. For example, the following program converts a byte value to its hexadecimal string<br /> representation. Notice that the shifted value is masked by ANDing it with 0x0f to discard<br /> any sign-extended bits so that the value can be used as an index into the array of hexadecimal<br /> characters.<br /> // Masking sign extension.<br /> class HexByte {<br /> static public void main(String args[]) {<br /> char hex[] = {<br /> '0', '1', '2', '3', '4', '5', '6', '7',<br /> '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'<br /> };<br /> byte b = (byte) 0xf1;<br /> }<br /> System.out.println("b = 0x" + hex[(b >> 4) & 0x0f] + hex[b & 0x0f]);<br /> }<br /> Here is the output of this program:<br /> b = 0xf1<br /> The Unsigned Right Shift<br /> As you have just seen, the >> operator automatically fills the high-order bit with its<br /> previous contents each time a shift occurs. This preserves the sign of the value. However,</div> <div>THE JAVA LIBRARY<br /> Chapter 14: Exploring java.lang 387<br /> Byte, Short, Integer, and Long<br /> The Byte, Short, Integer, and Long classes are wrappers for byte, short, int, and long<br /> integer types, respectively. Their constructors are shown here:<br /> Byte(byte num)<br /> Byte(String str) throws NumberFormatException<br /> Short(short num)<br /> Short(String str) throws NumberFormatException<br /> Integer(int num)<br /> Integer(String str) throws NumberFormatException<br /> Long(long num)<br /> Long(String str) throws NumberFormatException<br /> As you can see, these objects can be constructed from numeric values or from strings<br /> that contain valid whole number values.<br /> The methods defined by these classes are shown in Tables 14-3 through 14-6. As<br /> you can see, they define methods for parsing integers from strings and converting<br /> strings back into integers. Variants of these methods allow you to specify the radix,<br /> or numeric base, for conversion. Common radixes are 2 for binary, 8 for octal, 10 for<br /> decimal, and 16 for hexadecimal.<br /> The following constants are defined:<br /> MIN_VALUE<br /> MAX_VALUE<br /> TYPE<br /> Minimum value<br /> Maximum value<br /> The Class object for byte, short, int, or long<br /> Method<br /> byte byteValue( )<br /> int compareTo(Byte b)<br /> Description<br /> Returns the value of the invoking<br /> object as a byte.<br /> Compares the numerical value of<br /> the invoking object with that of b.<br /> Returns 0 if the values are equal.<br /> Returns a negative value if the<br /> invoking object has a lower value.<br /> Returns a positive value if the<br /> invoking object has a greater value.<br /> (Added by Java 2)<br /> Table 14-3.<br /> The Methods Defined by Byte</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 28: Migrating from C++ to Java 985<br /> ■ Java contains a built-in string type called String. String is somewhat similar<br /> to the standard string class type provided by C++. Of course, in C++ string is<br /> only available if you include its class declarations in your program. It is not a<br /> built-in type.<br /> Features That Differ<br /> There are some features common to both C++ and Java that each language handles a<br /> bit differently:<br /> ■ While both C++ and Java support a Boolean data type, Java does not implement<br /> true and false in the same way as C++. In C++, true is any nonzero value. False<br /> is zero. In Java, true and false are predefined literals, and these are the only<br /> values that a boolean expression may have. While C++ also defines true and<br /> false, which may be assigned to a bool variable, C++ automatically converts<br /> nonzero values into true and zero values into false. This does not occur in Java.<br /> ■ When you create a C++ class, the access specifiers apply to groups of<br /> statements. In Java, access specifiers apply only to the declarations that they<br /> immediately precede.<br /> ■ C++ supports exception handling that is fairly similar to Java’s. However,<br /> in C++ there is no requirement that a thrown exception be caught.<br /> With these additions, deletions, and differences as a backdrop, the rest of this<br /> chapter will look closely at a few of the key issues that you must deal with when<br /> converting code from C++ to Java.<br /> Eliminating Pointers<br /> When you convert a C++ program into Java, perhaps the greatest number of changes<br /> will be caused by pointers. Most C++ code is heavily dependent upon pointers for its<br /> operation. You can’t program anything very significant in C++ without using a pointer.<br /> There are four general categories of pointer usage that you will encounter in<br /> C++ code:<br /> ■ As parameters to functions. Although C++ supports the reference parameter,<br /> there is a large base of legacy code that was originally written in C. C does not<br /> support reference parameters. In C, if a function needs to change the value of an<br /> argument, it is necessary to explicitly pass a pointer to that argument. Therefore,<br /> it is still common to find pointer parameters used in C++ code that was originally<br /> ported from C. Also, in some cases the same function library will need to be<br /> shared by both C and C++ code, which prevents the use of reference parameters.</div> <div>958 Java™ 2: The Complete Reference<br /> Method<br /> Object getAttribute(String attr)<br /> String getCharacterEncoding( )<br /> int getContentLength( )<br /> String getContentType( )<br /> ServletInputStream getInputStream( )<br /> throws IOException<br /> String getParameter(String pname)<br /> Enumeration getParameterNames( )<br /> String[ ] getParameterValues(String name )<br /> String getProtocol( )<br /> BufferedReader getReader( )<br /> throws IOException<br /> Description<br /> Returns the value of the attribute<br /> named attr.<br /> Returns the character encoding of<br /> the request.<br /> Returns the size of the request. The<br /> value –1 is returned if the size is<br /> unavailable.<br /> Returns the type of the request. A<br /> null value is returned if the type<br /> cannot be determined.<br /> Returns a ServletInputStream<br /> that can be used to read binary<br /> data from the request. An<br /> IllegalStateException is thrown<br /> if getReader( ) has already been<br /> invoked for this request.<br /> Returns the value of the parameter<br /> named pname.<br /> Returns an enumeration of the<br /> parameter names for this request.<br /> Returns an array containing values<br /> associated with the parameter<br /> specified by name.<br /> Returns a description of the<br /> protocol.<br /> Returns a buffered reader that<br /> can be used to read text from the<br /> request. An IllegalStateException<br /> is thrown if getInputStream( ) has<br /> already been invoked for this<br /> request.<br /> Table 27-3.<br /> Various Methods Defined by ServletRequest</div> <div>THE JAVA LIBRARY<br /> Chapter 13: String Handling 369<br /> Notice that several of these methods work with regular expressions. Support for<br /> regular expression processing was added by Java 2, version 1.4 and is described in<br /> Chapter 24.<br /> StringBuffer<br /> StringBuffer is a peer class of String that provides much of the functionality of strings.<br /> As you know, String represents fixed-length, immutable character sequences. In contrast,<br /> StringBuffer represents growable and writeable character sequences. StringBuffer<br /> may have characters and substrings inserted in the middle or appended to the end.<br /> StringBuffer will automatically grow to make room for such additions and often has<br /> more characters preallocated than are actually needed, to allow room for growth. Java<br /> uses both classes heavily, but many programmers deal only with String and let Java<br /> manipulate StringBuffers behind the scenes by using the overloaded + operator.<br /> StringBuffer Constructors<br /> StringBuffer defines these three constructors:<br /> StringBuffer( )<br /> StringBuffer(int size)<br /> StringBuffer(String str)<br /> The default constructor (the one with no parameters) reserves room for 16<br /> characters without reallocation. The second version accepts an integer argument that<br /> explicitly sets the size of the buffer. The third version accepts a String argument that<br /> sets the initial contents of the StringBuffer object and reserves room for 16 more<br /> characters without reallocation. StringBuffer allocates room for 16 additional<br /> characters when no specific buffer length is requested, because reallocation is a costly<br /> process in terms of time. Also, frequent reallocations can fragment memory. By<br /> allocating room for a few extra characters, StringBuffer reduces the number of<br /> reallocations that take place.<br /> length( ) and capacity( )<br /> The current length of a StringBuffer can be found via the length( ) method, while the<br /> total allocated capacity can be found through the capacity( ) method. They have the<br /> following general forms:<br /> int length( )<br /> int capacity( )</div> <div>Appendix A: Using Java’s Documentation Comments 1135<br /> As you can see, all document tags begin with an at sign (@). You may also use<br /> other, standard HTML tags in a documentation comment. However, some tags, such as<br /> headings, should not be used, because they disrupt the look of the HTML file produced<br /> by javadoc.<br /> You can use documentation comments to document classes, interfaces, fields,<br /> constructors, and methods. In all cases, the documentation comment must immediately<br /> precede the item being documented. When you are documenting a variable, the<br /> documentation tags you can use are @see, @since, @serial, @serialField, {@value},<br /> and @deprecated. For classes, you can use @see, @author, @since, @deprecated, and<br /> @version. Methods can be documented with @see, @return, @param, @since,<br /> @deprecated, @throws, @serialData, {@inheritDoc}, and @exception. A {@link},<br /> {@docRoot}, or {@linkplain} tag can be used anywhere. Each tag is examined next.<br /> @author<br /> The @author tag documents the author of a class. It has the following syntax:<br /> @author description<br /> Here, description will usually be the name of the person who wrote the class. The<br /> @author tag can be used only in documentation for a class. You may need to specify<br /> the -author option when executing javadoc in order for the @author field to be<br /> included in the HTML documentation.<br /> @deprecated<br /> The @deprecated tag specifies that a class or a member is deprecated. It is recommended<br /> that you include @see or {@link} tags to inform the programmer about available<br /> alternatives. The syntax is the following:<br /> @deprecated description<br /> Here, description is the message that describes the deprecation. Information specified by<br /> the @deprecated tag is recognized by the compiler and is included in the .class file that<br /> is generated. Therefore, the programmer can be given this information when compiling<br /> Java source files. The @deprecated tag can be used in documentation for variables,<br /> methods, and classes.<br /> {@docRoot}<br /> {@docRoot} specifies the path to the root directory of the current documentation.<br /> @exception<br /> The @exception tag describes an exception to a method. It has the following syntax:<br /> @exception exception-name explanation</div> <div>218 Java™ 2: The Complete Reference<br /> }<br /> double dim1;<br /> double dim2;<br /> Figure(double a, double b) {<br /> dim1 = a;<br /> dim2 = b;<br /> }<br /> // area is now an abstract method<br /> abstract double area();<br /> class Rectangle extends Figure {<br /> Rectangle(double a, double b) {<br /> super(a, b);<br /> }<br /> }<br /> // override area for rectangle<br /> double area() {<br /> System.out.println("Inside Area for Rectangle.");<br /> return dim1 * dim2;<br /> }<br /> class Triangle extends Figure {<br /> Triangle(double a, double b) {<br /> super(a, b);<br /> }<br /> }<br /> // override area for right triangle<br /> double area() {<br /> System.out.println("Inside Area for Triangle.");<br /> return dim1 * dim2 / 2;<br /> }<br /> class AbstractAreas {<br /> public static void main(String args[]) {<br /> // Figure f = new Figure(10, 10); // illegal now<br /> Rectangle r = new Rectangle(9, 5);<br /> Triangle t = new Triangle(10, 8);</div> <div>xviii Java™ 2: The Complete Reference<br /> The MouseWheelEvent Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 665<br /> The TextEvent Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 666<br /> The WindowEvent Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 667<br /> Sources of Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 668<br /> Event Listener Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 669<br /> The ActionListener Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 670<br /> The AdjustmentListener Interface . . . . . . . . . . . . . . . . . . . . . . . . . . 670<br /> The ComponentListener Interface . . . . . . . . . . . . . . . . . . . . . . . . . . 670<br /> The ContainerListener Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . 670<br /> The FocusListener Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 670<br /> The ItemListener Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671<br /> The KeyListener Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671<br /> The MouseListener Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671<br /> The MouseMotionListener Interface . . . . . . . . . . . . . . . . . . . . . . . . 671<br /> The MouseWheelListener Interface . . . . . . . . . . . . . . . . . . . . . . . . . 672<br /> The TextListener Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 672<br /> The WindowFocusListener Interface . . . . . . . . . . . . . . . . . . . . . . . . 672<br /> The WindowListener Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 672<br /> Using the Delegation Event Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 673<br /> Handling Mouse Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 673<br /> Handling Keyboard Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 676<br /> Adapter Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 680<br /> Inner Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 682<br /> Anonymous Inner Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 684<br /> 21 Introducing the AWT: Working with Windows,<br /> Graphics, and Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687<br /> AWT Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 688<br /> Window Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 691<br /> Component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 691<br /> Container . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692<br /> Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 692<br /> Window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693<br /> Frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693<br /> Canvas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693<br /> Working with Frame Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 693<br /> Setting the Window’s Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . 694<br /> Hiding and Showing a Window . . . . . . . . . . . . . . . . . . . . . . . . . . . . 694<br /> Setting a Window’s Title . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 694<br /> Closing a Frame Window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 694<br /> Creating a Frame Window in an Applet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 695<br /> Handling Events in a Frame Window . . . . . . . . . . . . . . . . . . . . . . . 697<br /> Creating a Windowed Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702<br /> Displaying Information Within a Window . . . . . . . . . . . . . . . . . . . . . . . . . . . 704<br /> Working with Graphics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705<br /> Drawing Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 705<br /> Drawing Rectangles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 706<br /> Drawing Ellipses and Circles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 708</div> <div>1072 Java™ 2: The Complete Reference<br /> Figure 32-1.<br /> The user must type in his or her name to begin<br /> Figure 32-2.<br /> The list of competitors</div> <div>THE JAVA LANGUAGE<br /> Chapter 11: Multithreaded Programming 311<br /> Using Multithreading<br /> If you are like most programmers, having multithreaded support built into the language<br /> will be new to you. The key to utilizing this support effectively is to think concurrently<br /> rather than serially. For example, when you have two subsystems within a program<br /> that can execute concurrently, make them individual threads. With the careful use of<br /> multithreading, you can create very efficient programs. A word of caution is in order,<br /> however: If you create too many threads, you can actually degrade the performance<br /> of your program rather than enhance it. Remember, some overhead is associated with<br /> context switching. If you create too many threads, more CPU time will be spent changing<br /> contexts than executing your program!</div> <div>142 Java™ 2: The Complete Reference<br /> As you can see, when volume( ) is called, it is put on the right side of an assignment<br /> statement. On the left is a variable, in this case vol, that will receive the value returned<br /> by volume( ). Thus, after<br /> vol = mybox1.volume();<br /> executes, the value of mybox1.volume( ) is 3,000 and this value then is stored in vol.<br /> There are two important things to understand about returning values:<br /> ■ The type of data returned by a method must be compatible with the return type<br /> specified by the method. For example, if the return type of some method is<br /> boolean, you could not return an integer.<br /> ■ The variable receiving the value returned by a method (such as vol, in this case)<br /> must also be compatible with the return type specified for the method.<br /> One more point: The preceding program can be written a bit more efficiently<br /> because there is actually no need for the vol variable. The call to volume( ) could have<br /> been used in the println( ) statement directly, as shown here:<br /> System.out.println("Volume is " + mybox1.volume());<br /> In this case, when println( ) is executed, mybox1.volume( ) will be called automatically<br /> and its value will be passed to println( ).<br /> Adding a Method That Takes Parameters<br /> While some methods don’t need parameters, most do. Parameters allow a method to be<br /> generalized. That is, a parameterized method can operate on a variety of data and/or<br /> be used in a number of slightly different situations. To illustrate this point, let’s use<br /> a very simple example. Here is a method that returns the square of the number 10:<br /> int square()<br /> {<br /> return 10 * 10;<br /> }<br /> While this method does, indeed, return the value of 10 squared, its use is very<br /> limited. However, if you modify the method so that it takes a parameter, as shown<br /> next, then you can make square( ) much more useful.</div> <div>104 Java™ 2: The Complete Reference<br /> You might want to experiment with this program before moving on. As you will<br /> find, no matter what value you give month, one and only one assignment statement<br /> within the ladder will be executed.<br /> switch<br /> The switch statement is Java’s multiway branch statement. It provides an easy way to<br /> dispatch execution to different parts of your code based on the value of an expression.<br /> As such, it often provides a better alternative than a large series of if-else-if statements.<br /> Here is the general form of a switch statement:<br /> switch (expression) {<br /> case value1:<br /> // statement sequence<br /> break;<br /> case value2:<br /> // statement sequence<br /> break;<br /> .<br /> .<br /> .<br /> case valueN:<br /> // statement sequence<br /> break;<br /> default:<br /> // default statement sequence<br /> }<br /> The expression must be of type byte, short, int, or char; each of the values specified<br /> in the case statements must be of a type compatible with the expression. Each case<br /> value must be a unique literal (that is, it must be a constant, not a variable). Duplicate<br /> case values are not allowed.<br /> The switch statement works like this: The value of the expression is compared with<br /> each of the literal values in the case statements. If a match is found, the code sequence<br /> following that case statement is executed. If none of the constants matches the value of<br /> the expression, then the default statement is executed. However, the default statement<br /> is optional. If no case matches and no default is present, then no further action is taken.<br /> The break statement is used inside the switch to terminate a statement sequence.<br /> When a break statement is encountered, execution branches to the first line of code that<br /> follows the entire switch statement. This has the effect of “jumping out” of the switch.<br /> Here is a simple example that uses a switch statement:</div> <div>196 Java™ 2: The Complete Reference<br /> }<br /> }<br /> height = h;<br /> depth = d;<br /> color = c;<br /> Remember, once you have created a superclass that defines the general aspects of<br /> an object, that superclass can be inherited to form specialized classes. Each subclass<br /> simply adds its own, unique attributes. This is the essence of inheritance.<br /> A Superclass Variable Can Reference a Subclass Object<br /> A reference variable of a superclass can be assigned a reference to any subclass derived<br /> from that superclass. You will find this aspect of inheritance quite useful in a variety of<br /> situations. For example, consider the following:<br /> class RefDemo {<br /> public static void main(String args[]) {<br /> BoxWeight weightbox = new BoxWeight(3, 5, 7, 8.37);<br /> Box plainbox = new Box();<br /> double vol;<br /> vol = weightbox.volume();<br /> System.out.println("Volume of weightbox is " + vol);<br /> System.out.println("Weight of weightbox is " +<br /> weightbox.weight);<br /> System.out.println();<br /> // assign BoxWeight reference to Box reference<br /> plainbox = weightbox;<br /> vol = plainbox.volume(); // OK, volume() defined in Box<br /> System.out.println("Volume of plainbox is " + vol);<br /> /* The following statement is invalid because plainbox<br /> does not define a weight member. */<br /> // System.out.println("Weight of plainbox is " + plainbox.weight);<br /> }<br /> }</div> <div>536 Java™ 2: The Complete Reference<br /> The java.util.zip Package<br /> The java.util.zip package provides the ability to read and write files in the popular ZIP<br /> and GZIP file formats. Both ZIP and GZIP input and output streams are available.<br /> Other classes implement the ZLIB algorithms for compression and decompression.<br /> The java.util.jar Package<br /> The java.util.jar package provides the ability to read and write Java Archive (JAR)<br /> files. You will see in Chapter 25 that JAR files are used to contain software components<br /> known as Java Beans and any associated files.</div> <div>766 Java™ 2: The Complete Reference<br /> }<br /> }<br /> msg = "Current state: ";<br /> g.drawString(msg, 6, 80);<br /> msg = " Windows 98/XP: " + Win98.getState();<br /> g.drawString(msg, 6, 100);<br /> msg = " Windows NT/2000: " + winNT.getState();<br /> g.drawString(msg, 6, 120);<br /> msg = " Solaris: " + solaris.getState();<br /> g.drawString(msg, 6, 140);<br /> msg = " Mac: " + mac.getState();<br /> g.drawString(msg, 6, 160);<br /> Following is sample output generated by the FlowLayoutDemo applet:<br /> Compare this with the output from the CheckboxDemo applet, shown earlier in<br /> Figure 22-2.<br /> BorderLayout<br /> The BorderLayout class implements a common layout style for top-level windows. It<br /> has four narrow, fixed-width components at the edges and one large area in the center.<br /> The four sides are referred to as north, south, east, and west. The middle area is called<br /> the center. Here are the constructors defined by BorderLayout:<br /> BorderLayout( )<br /> BorderLayout(int horz, int vert)</div> <div>282 Java™ 2: The Complete Reference<br /> Inside NewThread’s constructor, a new Thread object is created by the following<br /> statement:<br /> t = new Thread(this, "Demo Thread");<br /> Passing this as the first argument indicates that you want the new thread to call the<br /> run( ) method on this object. Next, start( ) is called, which starts the thread of execution<br /> beginning at the run( ) method. This causes the child thread’s for loop to begin. After<br /> calling start( ), NewThread’s constructor returns to main( ). When the main thread<br /> resumes, it enters its for loop. Both threads continue running, sharing the CPU, until<br /> their loops finish. The output produced by this program is as follows:<br /> Child thread: Thread[Demo Thread,5,main]<br /> Main Thread: 5<br /> Child Thread: 5<br /> Child Thread: 4<br /> Main Thread: 4<br /> Child Thread: 3<br /> Child Thread: 2<br /> Main Thread: 3<br /> Child Thread: 1<br /> Exiting child thread.<br /> Main Thread: 2<br /> Main Thread: 1<br /> Main thread exiting.<br /> As mentioned earlier, in a multithreaded program, often the main thread must<br /> be the last thread to finish running. In fact, for some older JVMs, if the main thread<br /> finishes before a child thread has completed, then the Java run-time system may<br /> “hang.” The preceding program ensures that the main thread finishes last, because<br /> the main thread sleeps for 1,000 milliseconds between iterations, but the child thread<br /> sleeps for only 500 milliseconds. This causes the child thread to terminate earlier than<br /> the main thread. Shortly, you will see a better way to wait for a thread to finish.<br /> Extending Thread<br /> The second way to create a thread is to create a new class that extends Thread,<br /> and then to create an instance of that class. The extending class must override the<br /> run( ) method, which is the entry point for the new thread. It must also call start( )<br /> to begin execution of the new thread. Here is the preceding program rewritten to<br /> extend Thread:</div> <div>THE JAVA LIBRARY<br /> Chapter 21: Introducing the AWT: Working with Windows, Graphics, and Text 713<br /> The second color constructor takes a single integer that contains the mix of red, green,<br /> and blue packed into an integer. The integer is organized with red in bits 16 to 23,<br /> green in bits 8 to 15, and blue in bits 0 to 7. Here is an example of this constructor:<br /> int newRed = (0xff000000 | (0xc0 << 16) | (0x00 << 8) | 0x00);<br /> Color darkRed = new Color(newRed);<br /> The final constructor, Color(float, float, float), takes three float values (between 0.0<br /> and 1.0) that specify the relative mix of red, green, and blue.<br /> Once you have created a color, you can use it to set the foreground and/or<br /> background color by using the setForeground( ) and setBackground( ) methods<br /> described in Chapter 19. You can also select it as the current drawing color.<br /> Color Methods<br /> The Color class defines several methods that help manipulate colors. They are<br /> examined here.<br /> Using Hue, Saturation, and Brightness<br /> The hue-saturation-brightness (HSB) color model is an alternative to red-green-blue<br /> (RGB) for specifying particular colors. Figuratively, hue is a wheel of color. The hue is<br /> specified with a number between 0.0 and 1.0 (the colors are approximately: red, orange,<br /> yellow, green, blue, indigo, and violet). Saturation is another scale ranging from 0.0 to<br /> 1.0, representing light pastels to intense hues. Brightness values also range from 0.0 to<br /> 1.0, where 1 is bright white and 0 is black. Color supplies two methods that let you<br /> convert between RGB and HSB. They are shown here:<br /> static int HSBtoRGB(float hue, float saturation, float brightness)<br /> static float[ ] RGBtoHSB(int red, int green, int blue, float values[ ])<br /> HSBtoRGB( ) returns a packed RGB value compatible with the Color(int) constructor.<br /> RGBtoHSB( ) returns a float array of HSB values corresponding to RGB integers. If<br /> values is not null, then this array is given the HSB values and returned. Otherwise, a<br /> new array is created and the HSB values are returned in it. In either case, the array<br /> contains the hue at index 0, saturation at index 1, and brightness at index 2.<br /> getRed( ), getGreen( ), getBlue( )<br /> You can obtain the red, green, and blue components of a color independently using<br /> getRed( ), getGreen( ), and getBlue( ), shown here:<br /> int getRed( )<br /> int getGreen( )<br /> int getBlue( )</div> <div>1046 Java™ 2: The Complete Reference</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 27: Servlets 965<br /> The HttpServletResponse Interface<br /> The HttpServletResponse interface is implemented by the server. It enables a servlet<br /> to formulate an HTTP response to a client. Several constants are defined. These<br /> correspond to the different status codes that can be assigned to an HTTP response. For<br /> example, SC_OK indicates that the HTTP request succeeded and SC_NOT_FOUND<br /> indicates that the requested resource is not available. Several methods of this interface<br /> are summarized in Table 27-6.<br /> Method<br /> void addCookie(Cookie cookie)<br /> boolean containsHeader(String field)<br /> String encodeURL(String url)<br /> String encodeRedirectURL(String url)<br /> void sendError(int c)<br /> throws IOException<br /> void sendError(int c, String s)<br /> throws IOException<br /> void sendRedirect(String url)<br /> throws IOException<br /> Description<br /> Adds cookie to the HTTP response.<br /> Returns true if the HTTP response<br /> header contains a field named field.<br /> Determines if the session ID must<br /> be encoded in the URL identified<br /> as url. If so, returns the modified<br /> version of url. Otherwise, returns<br /> url. All URLs generated by a<br /> servlet should be processed by<br /> this method.<br /> Determines if the session ID<br /> must be encoded in the URL<br /> identified as url. If so, returns<br /> the modified version of url.<br /> Otherwise, returns url. All URLs<br /> passed to sendRedirect( ) should<br /> be processed by this method.<br /> Sends the error code c to the client.<br /> Sends the error code c and message<br /> s to the client.<br /> Redirects the client to url.<br /> Table 27-6.<br /> Various Methods Defined by HttpServletResponse</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 26: A Tour of Swing 939<br /> Scroll Panes<br /> A scroll pane is a component that presents a rectangular area in which a component<br /> may be viewed. Horizontal and/or vertical scroll bars may be provided if necessary.<br /> Scroll panes are implemented in Swing by the JScrollPane class, which extends<br /> JComponent. Some of its constructors are shown here:<br /> JScrollPane(Component comp)<br /> JScrollPane(int vsb, int hsb)<br /> JScrollPane(Component comp, int vsb, int hsb)<br /> Here, comp is the component to be added to the scroll pane. vsb and hsb are int<br /> constants that define when vertical and horizontal scroll bars for this scroll pane are<br /> shown. These constants are defined by the ScrollPaneConstants interface. Some<br /> examples of these constants are described as follows:<br /> Constant<br /> HORIZONTAL_SCROLLBAR_ALWAYS<br /> HORIZONTAL_SCROLLBAR_AS_NEEDED<br /> VERTICAL_SCROLLBAR_ALWAYS<br /> VERTICAL_SCROLLBAR_AS_NEEDED<br /> Description<br /> Always provide horizontal<br /> scroll bar<br /> Provide horizontal scroll bar,<br /> if needed<br /> Always provide vertical<br /> scroll bar<br /> Provide vertical scroll bar,<br /> if needed<br /> Here are the steps that you should follow to use a scroll pane in an applet:<br /> 1. Create a JComponent object.<br /> 2. Create a JScrollPane object. (The arguments to the constructor specify the<br /> component and the policies for vertical and horizontal scroll bars.)<br /> 3. Add the scroll pane to the content pane of the applet.</div> <div>Chapter 22<br /> Using AWT Controls,<br /> Layout Managers,<br /> and Menus<br /> 735</div> <div>466 Java™ 2: The Complete Reference<br /> The Map.Entry Interface<br /> The Map.Entry interface enables you to work with a map entry. Recall that the<br /> entrySet( ) method declared by the Map interface returns a Set containing the map<br /> entries. Each of these set elements is a Map.Entry object. Table 15-8 summarizes the<br /> methods declared by this interface.<br /> The Map Classes<br /> Several classes provide implementations of the map interfaces. The classes that can be<br /> used for maps are summarized here:<br /> Class<br /> AbstractMap<br /> HashMap<br /> TreeMap<br /> WeakHashMap<br /> LinkedHashMap<br /> IdentityHashMap<br /> Description<br /> Implements most of the Map interface.<br /> Extends AbstractMap to use a hash table.<br /> Extends AbstractMap to use a tree.<br /> Extends AbstractMap to use a hash table with weak keys.<br /> Extends HashMap to allow insertion-order iterations.<br /> Extends AbstractMap and uses reference equality when<br /> comparing documents.<br /> Method<br /> boolean equals(Object obj)<br /> Object getKey( )<br /> Object getValue( )<br /> int hashCode( )<br /> Object setValue(Object v)<br /> Description<br /> Returns true if obj is a Map.Entry whose key and<br /> value are equal to that of the invoking object.<br /> Returns the key for this map entry.<br /> Returns the value for this map entry.<br /> Returns the hash code for this map entry.<br /> Sets the value for this map entry to v. A<br /> ClassCastException is thrown if v is not<br /> the correct type for the map. An<br /> IllegalArgumentException is thrown if there is<br /> a problem with v. A NullPointerException is<br /> thrown if v is null and the map does not permit<br /> null keys. An UnsupportedOperationException<br /> is thrown if the map cannot be changed.<br /> Table 15-8.<br /> The Methods Defined by Map.Entry</div> <div>854 Java™ 2: The Complete Reference<br /> For reading a file, use MapMode.READ. To read and write, use MapeMode.READ_<br /> WRITE. MapMode.PRIVATE causes a private copy of the file to be made and changes<br /> to the buffer do not affect the underlying file. The location within the file to begin<br /> mapping is specified by pos and the number of bytes to map are specified by size. A<br /> reference to this buffer is returned as a MappedByteBuffer, which is a subclass of<br /> ByteBuffer. Once the file has been mapped to a buffer, you can read the file from<br /> that buffer.<br /> The following program reworks the first example so that it uses a mapped file.<br /> // Use a mapped file to read a text file.<br /> import java.io.*;<br /> import java.nio.*;<br /> import java.nio.channels.*;<br /> public class MappedChannelRead {<br /> public static void main(String args[]) {<br /> FileInputStream fIn;<br /> FileChannel fChan;<br /> long fSize;<br /> MappedByteBuffer mBuf;<br /> try {<br /> // First, open an file for input.<br /> fIn = new FileInputStream("test.txt");<br /> // Next, obtain a channel to that file.<br /> fChan = fIn.getChannel();<br /> // Get the size of the file.<br /> fSize = fChan.size();<br /> // Now, map the file into a buffer.<br /> mBuf = fChan.map(FileChannel.MapMode.READ_ONLY,<br /> 0, fSize);<br /> // Read bytes from the buffer.<br /> for(int i=0; i < fSize; i++)<br /> System.out.print((char)mBuf.get());<br /> fChan.close(); // close channel<br /> fIn.close(); // close file<br /> } catch (IOException exc) {</div> <div>THE JAVA LANGUAGE<br /> Chapter 5: Control Statements 117<br /> Using the comma, the preceding for loop can be more efficiently coded as shown here:<br /> // Using the comma.<br /> class Comma {<br /> public static void main(String args[]) {<br /> int a, b;<br /> }<br /> }<br /> for(a=1, b=4; a<b; a++, b--) {<br /> System.out.println("a = " + a);<br /> System.out.println("b = " + b);<br /> }<br /> In this example, the initialization portion sets the values of both a and b. The two<br /> comma-separated statements in the iteration portion are executed each time the loop<br /> repeats. The program generates the following output:<br /> a = 1<br /> b = 4<br /> a = 2<br /> b = 3<br /> If you are familiar with C/C++, then you know that in those languages the comma is<br /> an operator that can be used in any valid expression. However, this is not the case with<br /> Java. In Java, the comma is a separator that applies only to the for loop.<br /> Some for Loop Variations<br /> The for loop supports a number of variations that increase its power and applicability. The<br /> reason it is so flexible is that its three parts, the initialization, the conditional test, and<br /> the iteration, do not need to be used for only those purposes. In fact, the three sections<br /> of the for can be used for any purpose you desire. Let’s look at some examples.<br /> One of the most common variations involves the conditional expression. Specifically,<br /> this expression does not need to test the loop control variable against some target value.<br /> In fact, the condition controlling the for can be any Boolean expression. For example,<br /> consider the following fragment:<br /> boolean done = false;<br /> for(int i=1; !done; i++) {</div> <div>914 Java™ 2: The Complete Reference<br /> Next, we will add a label to the design. Click on the label button in the Swing<br /> palette. This instantiates a JLabel object, which is the Swing class for a label. Then,<br /> move the mouse to the designer and outline a rectangle near the top of the window.<br /> This defines were the text will go. Then, using the Property Inspector window, find<br /> the text entry. Change it to “Move slider or scroll bar.” After you do this, your screen<br /> will look like Figure 25-8. Now, find the horizontalAlignment field in the Property<br /> Inspector and change its value to CENTER. This will center the text within the label.<br /> Next, select a slider from the palette and add it to the designer. Then, add a scroll<br /> bar. The slider is an instance of the Swing class JSlider and the scroll bar is an instance<br /> Figure 25-8.<br /> After adding a label</div> <div>696 Java™ 2: The Complete Reference<br /> addWindowListener(adapter);<br /> }<br /> public void paint(Graphics g) {<br /> g.drawString("This is in frame window", 10, 40);<br /> }<br /> }<br /> class MyWindowAdapter extends WindowAdapter {<br /> SampleFrame sampleFrame;<br /> public MyWindowAdapter(SampleFrame sampleFrame) {<br /> this.sampleFrame = sampleFrame;<br /> }<br /> public void windowClosing(WindowEvent we) {<br /> sampleFrame.setVisible(false);<br /> }<br /> }<br /> // Create frame window.<br /> public class AppletFrame extends Applet {<br /> Frame f;<br /> public void init() {<br /> f = new SampleFrame("A Frame Window");<br /> }<br /> f.setSize(250, 250);<br /> f.setVisible(true);<br /> }<br /> public void start() {<br /> f.setVisible(true);<br /> }<br /> public void stop() {<br /> f.setVisible(false);<br /> }<br /> public void paint(Graphics g) {<br /> g.drawString("This is in applet window", 10, 20);<br /> }<br /> Sample output from this program is shown here:</div> <div>956 Java™ 2: The Complete Reference<br /> Method<br /> void destroy( )<br /> ServletConfig getServletConfig( )<br /> String getServletInfo( )<br /> void init(ServletConfig sc)<br /> throws ServletException<br /> void service(ServletRequest req,<br /> ServletResponse res)<br /> throws ServletException,<br /> IOException<br /> Description<br /> Called when the servlet is unloaded.<br /> Returns a ServletConfig object that contains<br /> any initialization parameters.<br /> Returns a string describing the servlet.<br /> Called when the servlet is initialized.<br /> Initialization parameters for the servlet can be<br /> obtained from sc.AnUnavailableException<br /> should be thrown if the servlet cannot be<br /> initialized.<br /> Called to process a request from a client. The<br /> request from the client can be read from req.<br /> The response to the client can be written to<br /> res. An exception is generated if a servlet or<br /> IO problem occurs.<br /> Table 27-1.<br /> The Methods Defined by Servlet<br /> The init( ), service( ), and destroy( ) methods are the life cycle methods of the<br /> servlet. These are invoked by the server. The getServletConfig( ) method is called by<br /> the servlet to obtain initialization parameters. A servlet developer overrides the<br /> getServletInfo( ) method to provide a string with useful information (for example,<br /> author, version, date, copyright). This method is also invoked by the server.<br /> The ServletConfig Interface<br /> The ServletConfig interface is implemented by the server. It allows a servlet to obtain<br /> configuration data when it is loaded. The methods declared by this interface are<br /> summarized here:<br /> Method<br /> ServletContext getServletContext( )<br /> String getInitParameter(String param)<br /> Enumeration getInitParameterNames( )<br /> String getServletName( )<br /> Description<br /> Returns the context for this servlet.<br /> Returns the value of the initialization<br /> parameter named param.<br /> Returns an enumeration of all<br /> initialization parameter names.<br /> Returns the name of the invoking servlet.</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 26: A Tour of Swing 923<br /> The Swing-related classes are contained in javax.swing and its subpackages, such<br /> as javax.swing.tree. Many other Swing-related classes and interfaces exist that are not<br /> examined in this chapter.<br /> The remainder of this chapter examines various Swing components and illustrates<br /> them through sample applets.<br /> JApplet<br /> Fundamental to Swing is the JApplet class, which extends Applet. Applets that use<br /> Swing must be subclasses of JApplet. JApplet is rich with functionality that is not<br /> found in Applet. For example, JApplet supports various “panes,” such as the content<br /> pane, the glass pane, and the root pane. For the examples in this chapter, we will not be<br /> using most of JApplet’s enhanced features. However, one difference between Applet<br /> and JApplet is important to this discussion, because it is used by the sample applets in<br /> this chapter. When adding a component to an instance of JApplet, do not invoke the<br /> add( ) method of the applet. Instead, call add( ) for the content pane of the JApplet<br /> object. The content pane can be obtained via the method shown here:<br /> Container getContentPane( )<br /> The add( ) method of Container can be used to add a component to a content pane.<br /> Its form is shown here:<br /> void add(comp)<br /> Here, comp is the component to be added to the content pane.<br /> Icons and Labels<br /> In Swing, icons are encapsulated by the ImageIcon class, which paints an icon from an<br /> image. Two of its constructors are shown here:<br /> ImageIcon(String filename)<br /> ImageIcon(URL url)<br /> The first form uses the image in the file named filename. The second form uses the<br /> image in the resource identified by url.</div> <div>This page intentionally left blank.</div> <div>THE JAVA LANGUAGE<br /> Chapter 12: I/O, Applets, and Other Topics 337<br /> // declare native method<br /> public native void test() ;<br /> }<br /> // load DLL that contains static method<br /> static {<br /> System.loadLibrary("NativeDemo");<br /> }<br /> Notice that the test( ) method is declared as native and has no body. This is the method<br /> that we will implement in C shortly. Also notice the static block. As explained earlier in<br /> this book, a static block is executed only once, when your program begins execution<br /> (or, more precisely, when its class is first loaded). In this case, it is used to load the<br /> dynamic link library that contains the native implementation of test( ). (You will see<br /> how to create this library soon.)<br /> The library is loaded by the loadLibrary( ) method, which is part of the System<br /> class. This is its general form:<br /> static void loadLibrary(String filename)<br /> Here, filename is a string that specifies the name of the file that holds the library. For the<br /> Windows environment, this file is assumed to have the .DLL extension.<br /> After you enter the program, compile it to produce NativeDemo.class. Next, you<br /> must use javah.exe to produce one file: NativeDemo.h. (javah.exe is included in the<br /> SDK.) You will include NativeDemo.h in your implementation of test( ). To produce<br /> NativeDemo.h, use the following command:<br /> javah -jni NativeDemo<br /> This command produces a header file called NativeDemo.h. This file must be included in<br /> the C file that implements test( ). The output produced by this command is shown here:<br /> /* DO NOT EDIT THIS FILE - it is machine generated */<br /> #include <jni.h><br /> /* Header for class NativeDemo */<br /> #ifndef _Included_NativeDemo<br /> #define _Included_NativeDemo<br /> #ifdef _ _cplusplus<br /> extern "C" {<br /> #endif<br /> /*</div> <div>990 Java™ 2: The Complete Reference<br /> Even though it is quite simple for C++ code, at first glance the line<br /> while(*p1) *p2++ = *p1++;<br /> still requires a moment of thought to decipher its exact operation. One of the<br /> advantages of Java is that it does not encourage the creation of such expressions<br /> in the first place. Here is the Java version of the program. As you can see, its purpose<br /> and effects are transparent.<br /> // Array copy without pointers using Java.<br /> class CopyArray {<br /> public static void main(String args[]) {<br /> int nums[] = {10, 12, 24, 45, 23, 19, 44,<br /> 88, 99, 65, 76, 12, 89, 0};<br /> int copy[] = new int[14];<br /> int i;<br /> // copy array<br /> for(i=0; nums[i]!=0; i++)<br /> copy[i] = nums[i];<br /> nums[i] = 0; // terminate copy with zero<br /> // Display contents of each array.<br /> System.out.println("Here is the original array:");<br /> for(i=0; nums[i]!=0; i++)<br /> System.out.print(nums[i] + " ");<br /> System.out.println();<br /> }<br /> }<br /> System.out.println("Here is the copy:");<br /> for(i=0; nums[i]!=0; i++)<br /> System.out.print(copy[i] + " ");<br /> System.out.println();<br /> Both versions of the program produce the following results:<br /> Here is the original array:<br /> 10 12 24 45 23 19 44 88 99 65 76 12 89<br /> Here is the copy:<br /> 10 12 24 45 23 19 44 88 99 65 76 12 89</div> <div>504 Java™ 2: The Complete Reference<br /> fout.close();<br /> }<br /> // Look up numbers given a name.<br /> do {<br /> System.out.println("Enter name to find" +<br /> " ('quit' to quit): ");<br /> name = br.readLine();<br /> if(name.equals("quit")) continue;<br /> }<br /> }<br /> number = (String) ht.get(name);<br /> System.out.println(number);<br /> } while(!name.equals("quit"));<br /> Collections Summary<br /> The collections framework gives you, the programmer, a powerful set of well-engineered<br /> solutions to some of programming’s most common tasks. Consider using a collection the<br /> next time that you need to store and retrieve information. Remember, collections need<br /> not be reserved for only the “large jobs,” such as corporate databases, mailing lists, or<br /> inventory systems. They are also effective when applied to smaller jobs. For example, a<br /> TreeMap would make an excellent collection to hold the directory structure of a set of<br /> files. A TreeSet could be quite useful for storing project-management information.<br /> Frankly, the types of problems that will benefit from a collections-based solution are<br /> limited only by your imagination.</div> <div>THE JAVA LANGUAGE<br /> Chapter 11: Multithreaded Programming 289<br /> Two exiting.<br /> Three exiting.<br /> One exiting.<br /> Thread One is alive: false<br /> Thread Two is alive: false<br /> Thread Three is alive: false<br /> Main thread exiting.<br /> As you can see, after the calls to join( ) return, the threads have stopped executing.<br /> Thread Priorities<br /> Thread priorities are used by the thread scheduler to decide when each thread should<br /> be allowed to run. In theory, higher-priority threads get more CPU time than lowerpriority<br /> threads. In practice, the amount of CPU time that a thread gets often depends<br /> on several factors besides its priority. (For example, how an operating system implements<br /> multitasking can affect the relative availability of CPU time.) A higher-priority thread<br /> can also preempt a lower-priority one. For instance, when a lower-priority thread is<br /> running and a higher-priority thread resumes (from sleeping or waiting on I/O, for<br /> example), it will preempt the lower-priority thread.<br /> In theory, threads of equal priority should get equal access to the CPU. But you need<br /> to be careful. Remember, Java is designed to work in a wide range of environments.<br /> Some of those environments implement multitasking fundamentally differently than<br /> others. For safety, threads that share the same priority should yield control once in<br /> a while. This ensures that all threads have a chance to run under a nonpreemptive<br /> operating system. In practice, even in nonpreemptive environments, most threads<br /> still get a chance to run, because most threads inevitably encounter some blocking<br /> situation, such as waiting for I/O. When this happens, the blocked thread is suspended<br /> and other threads can run. But, if you want smooth multithreaded execution, you are<br /> better off not relying on this. Also, some types of tasks are CPU-intensive. Such threads<br /> dominate the CPU. For these types of threads, you want to yield control occasionally,<br /> so that other threads can run.<br /> To set a thread’s priority, use the setPriority( ) method, which is a member of<br /> Thread. This is its general form:<br /> final void setPriority(int level)<br /> Here, level specifies the new priority setting for the calling thread. The value of level<br /> must be within the range MIN_PRIORITY and MAX_PRIORITY. Currently, these<br /> values are 1 and 10, respectively. To return a thread to default priority, specify<br /> NORM_PRIORITY, which is currently 5. These priorities are defined as final<br /> variables within Thread.</div> <div>300 Java™ 2: The Complete Reference<br /> Put: 2<br /> Put: 3<br /> Put: 4<br /> Put: 5<br /> Put: 6<br /> Put: 7<br /> Got: 7<br /> As you can see, after the producer put 1, the consumer started and got the same 1 five<br /> times in a row. Then, the producer resumed and produced 2 through 7 without letting<br /> the consumer have a chance to consume them.<br /> The proper way to write this program in Java is to use wait( ) and notify( ) to signal<br /> in both directions, as shown here:<br /> // A correct implementation of a producer and consumer.<br /> class Q {<br /> int n;<br /> boolean valueSet = false;<br /> synchronized int get() {<br /> if(!valueSet)<br /> try {<br /> wait();<br /> } catch(InterruptedException e) {<br /> System.out.println("InterruptedException caught");<br /> }<br /> }<br /> System.out.println("Got: " + n);<br /> valueSet = false;<br /> notify();<br /> return n;<br /> synchronized void put(int n) {<br /> if(valueSet)<br /> try {<br /> wait();<br /> } catch(InterruptedException e) {<br /> System.out.println("InterruptedException caught");<br /> }<br /> this.n = n;</div> <div>284 Java™ 2: The Complete Reference<br /> This program generates the same output as the preceding version. As you can see, the<br /> child thread is created by instantiating an object of NewThread, which is derived<br /> from Thread.<br /> Notice the call to super( ) inside NewThread. This invokes the following form of<br /> the Thread constructor:<br /> public Thread(String threadName)<br /> Here, threadName specifies the name of the thread.<br /> Choosing an Approach<br /> At this point, you might be wondering why Java has two ways to create child threads,<br /> and which approach is better. The answers to these questions turn on the same point.<br /> The Thread class defines several methods that can be overridden by a derived class.<br /> Of these methods, the only one that must be overridden is run( ). This is, of course, the<br /> same method required when you implement Runnable. Many Java programmers feel<br /> that classes should be extended only when they are being enhanced or modified in<br /> some way. So, if you will not be overriding any of Thread’s other methods, it is<br /> probably best simply to implement Runnable. This is up to you, of course. However,<br /> throughout the rest of this chapter, we will create threads by using classes that<br /> implement Runnable.<br /> Creating Multiple Threads<br /> So far, you have been using only two threads: the main thread and one child thread.<br /> However, your program can spawn as many threads as it needs. For example, the<br /> following program creates three child threads:<br /> // Create multiple threads.<br /> class NewThread implements Runnable {<br /> String name; // name of thread<br /> Thread t;<br /> NewThread(String threadname) {<br /> name = threadname;<br /> t = new Thread(this, name);<br /> System.out.println("New thread: " + t);<br /> t.start(); // Start the thread<br /> }<br /> // This is the entry point for thread.<br /> public void run() {</div> <div>THE JAVA LANGUAGE<br /> Chapter 6: Introducing Classes 135<br /> This reference is then stored in the variable. Thus, in Java, all class objects must be<br /> dynamically allocated. Let’s look at the details of this procedure.<br /> In the preceding sample programs, a line similar to the following is used to declare<br /> an object of type Box:<br /> Box mybox = new Box();<br /> This statement combines the two steps just described. It can be rewritten like this to<br /> show each step more clearly:<br /> Box mybox; // declare reference to object<br /> mybox = new Box(); // allocate a Box object<br /> The first line declares mybox as a reference to an object of type Box. After this line<br /> executes, mybox contains the value null, which indicates that it does not yet point to<br /> an actual object. Any attempt to use mybox at this point will result in a compile-time<br /> error. The next line allocates an actual object and assigns a reference to it to mybox.<br /> After the second line executes, you can use mybox as if it were a Box object. But in<br /> reality, mybox simply holds the memory address of the actual Box object. The effect<br /> of these two lines of code is depicted in Figure 6-1.<br /> Figure 6-1.<br /> Declaring an object of type Box</div> <div>694 Java™ 2: The Complete Reference<br /> Setting the Window’s Dimensions<br /> The setSize( ) method is used to set the dimensions of the window. Its signature is<br /> shown here:<br /> void setSize(int newWidth, int newHeight)<br /> void setSize(Dimension newSize)<br /> The new size of the window is specified by newWidth and newHeight, or by the width<br /> and height fields of the Dimension object passed in newSize. The dimensions are<br /> specified in terms of pixels.<br /> The getSize( ) method is used to obtain the current size of a window. Its signature<br /> is shown here:<br /> Dimension getSize( )<br /> This method returns the current size of the window contained within the width and<br /> height fields of a Dimension object.<br /> Hiding and Showing a Window<br /> After a frame window has been created, it will not be visible until you call<br /> setVisible( ). Its signature is shown here:<br /> void setVisible(boolean visibleFlag)<br /> The component is visible if the argument to this method is true. Otherwise, it is hidden.<br /> Setting a Window’s Title<br /> You can change the title in a frame window using setTitle( ), which has this<br /> general form:<br /> void setTitle(String newTitle)<br /> Here, newTitle is the new title for the window.<br /> Closing a Frame Window<br /> When using a frame window, your program must remove that window from the<br /> screen when it is closed, by calling setVisible(false). To intercept a window-close<br /> event, you must implement the windowClosing( ) method of the WindowListener<br /> interface. Inside windowClosing( ), you must remove the window from the screen.<br /> The example in the next section illustrates this technique.</div> <div>APPLYING JAVA<br /> Chapter 32: Scrabblet: A Multiplayer Word Game 1131<br /> }<br /> public void run() {<br /> String s;<br /> StringTokenizer st;<br /> while ((s = readline()) != null) {<br /> st = new StringTokenizer(s);<br /> String keyword = st.nextToken();<br /> switch (lookup(keyword)) {<br /> default:<br /> System.out.println("bogus keyword: " + keyword + "\r");<br /> break;<br /> case NAME:<br /> name = st.nextToken() +<br /> (st.hasMoreTokens() ? " " + st.nextToken(CRLF) : "");<br /> System.out.println("[" + new Date() + "] " + this + "\r");<br /> server.set(id, this);<br /> break;<br /> case QUIT:<br /> close();<br /> return;<br /> case TO:<br /> String dest = st.nextToken();<br /> String body = st.nextToken(CRLF);<br /> server.sendto(dest, body);<br /> break;<br /> case DELETE:<br /> busy = true;<br /> server.delete(id);<br /> break;<br /> }<br /> }<br /> close();<br /> }<br /> Enhancing Scrabblet<br /> This applet represents a complete client/server, multiplayer board game. In the future,<br /> the code in Server and ServerConnection could be extended in many ways. It could be<br /> used to support other turn-based games. It could track and maintain a high-score list<br /> for each game. It could be dynamically extensible to understand new protocol verbs.</div> <div>THE JAVA LIBRARY<br /> Chapter 22: Using AWT Controls, Layout Managers, and Menus 797<br /> Extending Scrollbar<br /> The following program creates an applet that displays a scroll bar. When this control<br /> is manipulated, a string is displayed on the status line of the applet viewer or browser.<br /> That string includes the value represented by the scroll bar.<br /> There is one top-level class named ScrollbarDemo2 that extends Applet. Its init( )<br /> method creates a scroll bar element and adds it to the applet. MyScrollbar is an inner<br /> class that extends Scrollbar. It calls enableEvents( ) so that adjustment events may be<br /> received by this object. When the scroll bar is manipulated, processAdjustmentEvent( )<br /> is called. When an entry is selected, processAdjustmentEvent( ) is called. It displays<br /> a string and then hands control to the superclass.<br /> /*<br /> * <applet code=ScrollbarDemo2 width=300 height=100><br /> * </applet><br /> */<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import java.applet.*;<br /> public class ScrollbarDemo2 extends Applet {<br /> MyScrollbar myScrollbar;<br /> public void init() {<br /> myScrollbar = new MyScrollbar(Scrollbar.HORIZONTAL,<br /> 0, 1, 0, 100);<br /> add(myScrollbar);<br /> }<br /> class MyScrollbar extends Scrollbar {<br /> public MyScrollbar(int style, int initial, int thumb,<br /> int min, int max) {<br /> super(style, initial, thumb, min, max);<br /> enableEvents(AWTEvent.ADJUSTMENT_EVENT_MASK);<br /> }<br /> protected void processAdjustmentEvent(AdjustmentEvent ae) {<br /> showStatus("Adjustment event: " + ae.getValue());<br /> setValue(getValue());<br /> super.processAdjustmentEvent(ae);<br /> }<br /> }<br /> }</div> <div>THE JAVA LANGUAGE<br /> Chapter 1: The Genesis of Java 7<br /> C++ was invented by Bjarne Stroustrup in 1979, while he was working at Bell<br /> Laboratories in Murray Hill, New Jersey. Stroustrup initially called the new language<br /> “C with Classes.” However, in 1983, the name was changed to C++. C++ extends C<br /> by adding object-oriented features. Because C++ is built upon the foundation of C,<br /> it includes all of C’s features, attributes, and benefits. This is a crucial reason for the<br /> success of C++ as a language. The invention of C++ was not an attempt to create a<br /> completely new programming language. Instead, it was an enhancement to an already<br /> highly successful one.<br /> The Stage Is Set for Java<br /> By the end of the 1980s and the early 1990s, object-oriented programming using C++<br /> took hold. Indeed, for a brief moment it seemed as if programmers had finally found<br /> the perfect language. Because C++ blended the high efficiency and stylistic elements of<br /> C with the object-oriented paradigm, it was a language that could be used to create a<br /> wide range of programs. However, just as in the past, forces were brewing that would,<br /> once again, drive computer language evolution forward. Within a few years, the World<br /> Wide Web and the Internet would reach critical mass. This event would precipitate<br /> another revolution in programming.<br /> The Creation of Java<br /> Java was conceived by James Gosling, Patrick Naughton, Chris Warth, Ed Frank, and<br /> Mike Sheridan at Sun Microsystems, Inc. in 1991. It took 18 months to develop the first<br /> working version. This language was initially called “Oak” but was renamed “Java”<br /> in 1995. Between the initial implementation of Oak in the fall of 1992 and the public<br /> announcement of Java in the spring of 1995, many more people contributed to the design<br /> and evolution of the language. Bill Joy, Arthur van Hoff, Jonathan Payne, Frank Yellin,<br /> and Tim Lindholm were key contributors to the maturing of the original prototype.<br /> Somewhat surprisingly, the original impetus for Java was not the Internet! Instead,<br /> the primary motivation was the need for a platform-independent (that is, architectureneutral)<br /> language that could be used to create software to be embedded in various<br /> consumer electronic devices, such as microwave ovens and remote controls. As you<br /> can probably guess, many different types of CPUs are used as controllers. The trouble<br /> with C and C++ (and most other languages) is that they are designed to be compiled<br /> for a specific target. Although it is possible to compile a C++ program for just about<br /> any type of CPU, to do so requires a full C++ compiler targeted for that CPU. The<br /> problem is that compilers are expensive and time-consuming to create. An easier—<br /> and more cost-efficient—solution was needed. In an attempt to find such a solution,<br /> Gosling and others began work on a portable, platform-independent language that<br /> could be used to produce code that would run on a variety of CPUs under differing<br /> environments. This effort ultimately led to the creation of Java.</div> <div>908 Java™ 2: The Complete Reference<br /> Class<br /> DefaultPersistenceDelegate<br /> Encoder<br /> EventHandler<br /> EventSetDescriptor<br /> Expression<br /> FeatureDescriptor<br /> IndexedPropertyDescriptor<br /> IntrospectionException<br /> Introspector<br /> MethodDescriptor<br /> ParameterDescriptor<br /> PersistenceDelegate<br /> PropertyChangeEvent<br /> Description<br /> A concrete subclass of PersistenceDelegate.<br /> (Added by Java 2, version 1.4.)<br /> Encodes the state of a set of Beans. Can be used<br /> to write this information to a stream. (Added by<br /> Java 2, version 1.4.)<br /> Supports dynamic event listener creation.<br /> (Added by Java 2, version 1.4.)<br /> Instances of this class describe an event that can<br /> be generated by a Bean.<br /> Encapsulates a call to a method that returns a<br /> result. (Added by Java 2, version 1.4.)<br /> This is the superclass of the PropertyDescriptor,<br /> EventSetDescriptor, and MethodDescriptor<br /> classes.<br /> Instances of this class describe an indexed<br /> property of a Bean.<br /> An exception of this type is generated if a<br /> problem occurs when analyzing a Bean.<br /> This class analyzes a Bean and constructs a<br /> BeanInfo object that describes the component.<br /> Instances of this class describe a method of<br /> a Bean.<br /> Instances of this class describe a method<br /> parameter.<br /> Handles the state information of an object.<br /> (Added by Java 2, version 1.4.)<br /> This event is generated when bound or constrained<br /> properties are changed. It is sent to objects that<br /> registered an interest in these events and<br /> implement either the PropertyChangeListener or<br /> VetoableChangeListener interfaces.<br /> Table 25-3.<br /> The Classes Defined in java.beans (continued)</div> <div>560 Java™ 2: The Complete Reference<br /> class InputStreamEnumerator implements Enumeration {<br /> private Enumeration files;<br /> public InputStreamEnumerator(Vector files) {<br /> this.files = files.elements();<br /> }<br /> }<br /> public boolean hasMoreElements() {<br /> return files.hasMoreElements();<br /> }<br /> public Object nextElement() {<br /> try {<br /> return new FileInputStream(files.nextElement().toString());<br /> } catch (Exception e) {<br /> return null;<br /> }<br /> }<br /> class SequenceInputStreamDemo {<br /> public static void main(String args[]) throws Exception {<br /> int c;<br /> Vector files = new Vector();<br /> files.addElement("/autoexec.bat");<br /> files.addElement("/config.sys");<br /> InputStreamEnumerator e = new InputStreamEnumerator(files);<br /> InputStream input = new SequenceInputStream(e);<br /> }<br /> }<br /> while ((c = input.read()) != -1) {<br /> System.out.print((char) c);<br /> }<br /> input.close();<br /> This example creates a Vector and then adds two filenames to it. It passes that vector of<br /> names to the InputStreamEnumerator class, which is designed to provide a wrapper<br /> on the vector where the elements returned are not the filenames but rather open<br /> FileInputStreams on those names. The SequenceInputStream opens each file in turn,<br /> and this example prints the contents of the two files.</div> <div>THE JAVA LIBRARY<br /> Chapter 24: New I/O, Regular Expressions, and Other Packages 867<br /> Using replaceAll( )<br /> The replaceAll( ) method supplied by Matcher lets you perform powerful search and<br /> replace operations that use regular expressions. For example, the following program<br /> replaces all occurrences of sequences that begin with “Jon” with “Eric”.<br /> // Use replaceAll().<br /> import java.util.regex.*;<br /> class RegExpr8 {<br /> public static void main(String args[]) {<br /> String str = "Jon Jonathan Frank Ken Todd";<br /> Pattern pat = Pattern.compile("Jon.*? ");<br /> Matcher mat = pat.matcher(str);<br /> System.out.println("Original sequence: " + str);<br /> str = mat.replaceAll("Eric ");<br /> System.out.println("Modified sequence: " + str);<br /> }<br /> }<br /> The output is shown here:<br /> Original sequence: Jon Jonathan Frank Ken Todd<br /> Modified sequence: Eric Eric Frank Ken Todd<br /> Because the regular expression “Jon.*? “ matches any string that begins with Jon<br /> followed by zero or more characters, ending in a space, it can be used to match and<br /> replace both Jon and Jonathan with the name Eric. Such a substitution is not possible<br /> without pattern matching capabilities.<br /> Using split( )<br /> You can reduce an input sequence into its individual tokens by using the split( )<br /> method defined by Pattern. The split( ) method is shown here:<br /> String[ ] split(CharSequence str)<br /> It processes the input sequence passed in str, reducing it into tokens based on the<br /> delimiters specified by the pattern.</div> <div>1064 Java™ 2: The Complete Reference<br /> }<br /> }<br /> if ((c=(Color)clut.get(p)) == null)<br /> clut.put(p, c = new Color(p));<br /> return c;<br /> public void update() {}<br /> public void paint(Graphics g) {<br /> offgraphics.copyArea(bulbS, 0, bulbsW*bulbS-bulbS, d.height,<br /> -bulbS, 0);<br /> for (int y=0; y<bulbsH; y++) {<br /> offgraphics.setColor(color(scrollX, y));<br /> offgraphics.fillRect(d.width-bulbS, y*bulbS, bulbS, bulbS);<br /> }<br /> offgraphics.drawImage(bulb, d.width-bulbS, 0, null);<br /> g.drawImage(offscreen, 0, 0, null);<br /> scrollX = (scrollX + 1) % pixscan;<br /> }<br /> Thread t;<br /> public void run() {<br /> while (true) {<br /> paint(getGraphics());<br /> try{t.yield();} catch(Exception e) { };<br /> if(stopFlag)<br /> break;<br /> }<br /> }<br /> public void start() {<br /> t = new Thread(this);<br /> t.setPriority(Thread.MIN_PRIORITY);<br /> stopFlag = false;<br /> t.start();<br /> }<br /> public void stop() {<br /> stopFlag = true;<br /> }</div> <div>THE JAVA LIBRARY<br /> Chapter 16: java.util Part 2: More Utility Classes 527<br /> Observable<br /> The Observable class is used to create subclasses that other parts of your program can<br /> observe. When an object of such a subclass undergoes a change, observing classes are<br /> notified. Observing classes must implement the Observer interface, which defines the<br /> update( ) method. The update( ) method is called when an observer is notified of a<br /> change in an observed object.<br /> Observable defines the methods shown in Table 16-7. An object that is being<br /> observed must follow two simple rules. First, if it has changed, it must call<br /> setChanged( ). Second, when it is ready to notify observers of this change, it must call<br /> notifyObservers( ). This causes the update( ) method in the observing object(s) to be<br /> called. Be careful—if the object calls notifyObservers( ) without having previously<br /> called setChanged( ), no action will take place. The observed object must call both<br /> setChanged( ) and notifyObservers( ) before update( ) will be called.<br /> Method<br /> void addObserver(Observer obj)<br /> protected void clearChanged( )<br /> int countObservers( )<br /> void deleteObserver(Observer obj)<br /> void deleteObservers( )<br /> boolean hasChanged( )<br /> void notifyObservers( )<br /> void notifyObservers(Object obj)<br /> protected void setChanged( )<br /> Description<br /> Add obj to the list of objects observing the<br /> invoking object.<br /> Calling this method returns the status of the<br /> invoking object to “unchanged.”<br /> Returns the number of objects observing the<br /> invoking object.<br /> Removes obj from the list of objects<br /> observing the invoking object.<br /> Removes all observers for the invoking object.<br /> Returns true if the invoking object has been<br /> modified and false if it has not.<br /> Notifies all observers of the invoking object<br /> that it has changed by calling update( ). A<br /> null is passed as the second argument to<br /> update( ).<br /> Notifies all observers of the invoking object<br /> that it has changed by calling update( ). obj<br /> is passed as an argument to update( ).<br /> Called when the invoking object has changed.<br /> Table 16-7.<br /> The Methods Defined by Observable</div> <div>THE JAVA LANGUAGE<br /> Chapter 5: Control Statements 111<br /> to begin with.) As you can see, there is no need for a loop body; all of the action occurs<br /> within the conditional expression, itself. In professionally written Java code, short loops<br /> are frequently coded without bodies when the controlling expression can handle all of<br /> the details itself.<br /> do-while<br /> As you just saw, if the conditional expression controlling a while loop is initially false,<br /> then the body of the loop will not be executed at all. However, sometimes it is desirable<br /> to execute the body of a while loop at least once, even if the conditional expression is<br /> false to begin with. In other words, there are times when you would like to test the<br /> termination expression at the end of the loop rather than at the beginning. Fortunately,<br /> Java supplies a loop that does just that: the do-while. The do-while loop always executes<br /> its body at least once, because its conditional expression is at the bottom of the loop. Its<br /> general form is<br /> do {<br /> // body of loop<br /> } while (condition);<br /> Each iteration of the do-while loop first executes the body of the loop and then<br /> evaluates the conditional expression. If this expression is true, the loop will repeat.<br /> Otherwise, the loop terminates. As with all of Java’s loops, condition must be a Boolean<br /> expression.<br /> Here is a reworked version of the “tick” program that demonstrates the do-while<br /> loop. It generates the same output as before.<br /> // Demonstrate the do-while loop.<br /> class DoWhile {<br /> public static void main(String args[]) {<br /> int n = 10;<br /> }<br /> }<br /> do {<br /> System.out.println("tick " + n);<br /> n--;<br /> } while(n > 0);<br /> The loop in the preceding program, while technically correct, can be written more<br /> efficiently as follows:<br /> do {<br /> System.out.println("tick " + n);<br /> } while(--n > 0);</div> <div>THE JAVA LANGUAGE<br /> Chapter 3: Data Types, Variables, and Arrays 51<br /> Boolean Literals<br /> Boolean literals are simple. There are only two logical values that a boolean value can<br /> have, true and false. The values of true and false do not convert into any numerical<br /> representation. The true literal in Java does not equal 1, nor does the false literal equal 0.<br /> In Java, they can only be assigned to variables declared as boolean,orused in expressions<br /> with Boolean operators.<br /> Character Literals<br /> Characters in Java are indices into the Unicode character set. They are 16-bit values that<br /> can be converted into integers and manipulated with the integer operators, such as the<br /> addition and subtraction operators. A literal character is represented inside a pair of single<br /> quotes. All of the visible ASCII characters can be directly entered inside the quotes, such<br /> as ‘a’, ‘z’, and ‘@’. For characters that are impossible to enter directly, there are several<br /> escape sequences, which allow you to enter the character you need, such as ‘\’’ for the<br /> single-quote character itself, and ‘\n’ for the newline character. There is also a mechanism<br /> for directly entering the value of a character in octal or hexadecimal. For octal notation<br /> use the backslash followed by the three-digit number. For example, ‘\141’ is the letter ‘a’.<br /> For hexadecimal, you enter a backslash-u (\u), then exactly four hexadecimal digits. For<br /> example, ‘\u0061’ is the ISO-Latin-1 ‘a’ because the top byte is zero. ‘\ua432’ is a Japanese<br /> Katakana character. Table 3-1 shows the character escape sequences.<br /> Escape Sequence Description<br /> \ddd<br /> Octal character (ddd)<br /> \uxxxx<br /> Hexadecimal UNICODE character (xxxx)<br /> \’ Single quote<br /> \” Double quote<br /> \\ Backslash<br /> \r Carriage return<br /> \n New line (also known as line feed)<br /> \f Form feed<br /> \t Tab<br /> \b Backspace<br /> Table 3-1.<br /> Character Escape Sequences</div> <div>898 Java™ 2: The Complete Reference<br /> Figure 25-3.<br /> The Colors and OurButton Beans<br /> Create a New Bean<br /> Here are the steps that you must follow to create a new Bean:<br /> 1. Create a directory for the new Bean.<br /> 2. Create the Java source file(s).<br /> 3. Compile the source file(s).<br /> 4. Create a manifest file.<br /> 5. Generate a JAR file.<br /> 6. Start the BDK.<br /> 7. Test.<br /> The following sections discuss each of these steps in detail.<br /> Create a Directory for the New Bean<br /> You need to make a directory for the Bean. To follow along with this example, create<br /> c:\bdk\demo\sunw\demo\colors. Then change to that directory.</div> <div>706 Java™ 2: The Complete Reference<br /> </applet><br /> */<br /> public class Lines extends Applet {<br /> public void paint(Graphics g) {<br /> g.drawLine(0, 0, 100, 100);<br /> g.drawLine(0, 100, 100, 0);<br /> g.drawLine(40, 25, 250, 180);<br /> g.drawLine(75, 90, 400, 400);<br /> g.drawLine(20, 150, 400, 40);<br /> g.drawLine(5, 290, 80, 19);<br /> }<br /> }<br /> Sample output from this program is shown here:<br /> Drawing Rectangles<br /> The drawRect( ) and fillRect( ) methods display an outlined and filled rectangle,<br /> respectively. They are shown here:<br /> void drawRect(int top, int left, int width, int height)<br /> void fillRect(int top, int left, int width, int height)<br /> The upper-left corner of the rectangle is at top,left. The dimensions of the rectangle are<br /> specified by width and height.<br /> To draw a rounded rectangle, use drawRoundRect( ) or fillRoundRect( ), both<br /> shown here:<br /> void drawRoundRect(int top, int left, int width, int height,<br /> int xDiam, int yDiam)</div> <div>432 Java™ 2: The Complete Reference<br /> Two: 3<br /> One: 2<br /> Two: 2<br /> One: 1<br /> Two: 1<br /> One exiting.<br /> Two exiting.<br /> Main thread exiting.<br /> Inside the program, notice that thread group A is suspended for four seconds. As<br /> the output confirms, this causes threads One and Two to pause, but threads Three and<br /> Four continue running. After the four seconds, threads One and Two are resumed.<br /> Notice how thread group A is suspended and resumed. First, the threads in group A<br /> are obtained by calling enumerate( ) on group A. Then, each thread is suspended<br /> by iterating through the resulting array. To resume the threads in A, the list is<br /> again traversed and each thread is resumed. One last point: this example uses the<br /> recommended Java 2 approach to suspending and resuming threads. It does not rely<br /> upon the deprecated methods suspend( ) and resume( ).<br /> ThreadLocal and InheritableThreadLocal<br /> Java 2 added two thread-related classes to java.lang:<br /> ■ ThreadLocal Used to create thread local variables. Each thread will have its<br /> own copy of a thread local variable.<br /> ■ InheritableThreadLocal Creates thread local variables that may be inherited.<br /> Package<br /> Java 2 added a class called Package that encapsulates version data associated with a<br /> package. Package version information is becoming more important because of the<br /> proliferation of packages and because a Java program may need to know what version<br /> of a package is available. The methods defined by Package are shown in Table 14-18.<br /> The following program demonstrates Package, displaying the packages about which<br /> the program currently is aware.<br /> // Demonstrate Package<br /> class PkgTest {<br /> public static void main(String args[]) {<br /> Package pkgs[];</div> <div>Chapter28<br /> Migrating from C++<br /> to Java<br /> 981</div> <div>THE JAVA LANGUAGE<br /> Chapter 8: Inheritance 209<br /> }<br /> int k;<br /> B(int a, int b, int c) {<br /> super(a, b);<br /> k = c;<br /> }<br /> // display k – this overrides show() in A<br /> void show() {<br /> System.out.println("k: " + k);<br /> }<br /> class Override {<br /> public static void main(String args[]) {<br /> B subOb = new B(1, 2, 3);<br /> }<br /> }<br /> subOb.show(); // this calls show() in B<br /> The output produced by this program is shown here:<br /> k: 3<br /> When show( ) is invoked on an object of type B, the version of show( ) defined<br /> within B is used. That is, the version of show( ) inside B overrides the version<br /> declared in A.<br /> If you wish to access the superclass version of an overridden function, you can do<br /> so by using super. For example, in this version of B, the superclass version of show( ) is<br /> invoked within the subclass’ version. This allows all instance variables to be displayed.<br /> class B extends A {<br /> int k;<br /> B(int a, int b, int c) {<br /> super(a, b);<br /> k = c;<br /> }</div> <div>362 Java™ 2: The Complete Reference<br /> You can specify a starting point for the search using these forms:<br /> int indexOf(int ch, int startIndex)<br /> int lastIndexOf(int ch, int startIndex)<br /> int indexOf(String str, int startIndex)<br /> int lastIndexOf(String str, int startIndex)<br /> Here, startIndex specifies the index at which point the search begins. For indexOf( ),<br /> the search runs from startIndex to the end of the string. For lastIndexOf( ), the search<br /> runs from startIndex to zero.<br /> The following example shows how to use the various index methods to search<br /> inside of Strings:<br /> // Demonstrate indexOf() and lastIndexOf().<br /> class indexOfDemo {<br /> public static void main(String args[]) {<br /> String s = "Now is the time for all good men " +<br /> "to come to the aid of their country.";<br /> }<br /> }<br /> System.out.println(s);<br /> System.out.println("indexOf(t) = " +<br /> s.indexOf('t'));<br /> System.out.println("lastIndexOf(t) = " +<br /> s.lastIndexOf('t'));<br /> System.out.println("indexOf(the) = " +<br /> s.indexOf("the"));<br /> System.out.println("lastIndexOf(the) = " +<br /> s.lastIndexOf("the"));<br /> System.out.println("indexOf(t, 10) = " +<br /> s.indexOf('t', 10));<br /> System.out.println("lastIndexOf(t, 60) = " +<br /> s.lastIndexOf('t', 60));<br /> System.out.println("indexOf(the, 10) = " +<br /> s.indexOf("the", 10));<br /> System.out.println("lastIndexOf(the, 60) = " +<br /> s.lastIndexOf("the", 60));<br /> Here is the output of this program:<br /> Now is the time for all good men to come to the aid of their country.<br /> indexOf(t) = 7</div> <div>THE JAVA LIBRARY<br /> Chapter 15: java.util Part 1: The Collections Framework 485<br /> Enumeration specifies the following two methods:<br /> boolean hasMoreElements( )<br /> Object nextElement( )<br /> When implemented, hasMoreElements( ) must return true while there are still<br /> more elements to extract, and false when all the elements have been enumerated.<br /> nextElement( ) returns the next object in the enumeration as a generic Object reference.<br /> That is, each call to nextElement( ) obtains the next object in the enumeration. The<br /> calling routine must cast that object into the object type held in the enumeration.<br /> Vector<br /> Vector implements a dynamic array. It is similar to ArrayList, but with two differences:<br /> Vector is synchronized, and it contains many legacy methods that are not part of<br /> the collections framework. With the release of Java 2, Vector was reengineered to<br /> extend AbstractList and implement the List interface, so it now is fully compatible<br /> with collections.<br /> Here are the Vector constructors:<br /> Vector( )<br /> Vector(int size)<br /> Vector(int size, int incr)<br /> Vector(Collection c)<br /> The first form creates a default vector, which has an initial size of 10. The second form<br /> creates a vector whose initial capacity is specified by size. The third form creates a<br /> vector whose initial capacity is specified by size and whose increment is specified by<br /> incr. The increment specifies the number of elements to allocate each time that a vector<br /> is resized upward. The fourth form creates a vector that contains the elements of<br /> collection c. This constructor was added by Java 2.<br /> All vectors start with an initial capacity. After this initial capacity is reached, the<br /> next time that you attempt to store an object in the vector, the vector automatically<br /> allocates space for that object plus extra room for additional objects. By allocating more<br /> than just the required memory, the vector reduces the number of allocations that must<br /> take place. This reduction is important, because allocations are costly in terms of time.<br /> The amount of extra space allocated during each reallocation is determined by the<br /> increment that you specify when you create the vector. If you don’t specify an<br /> increment, the vector’s size is doubled by each allocation cycle.<br /> Vector defines these protected data members:<br /> int capacityIncrement;<br /> int elementCount;<br /> Object elementData[ ];</div> <div>THE JAVA LIBRARY<br /> Chapter 15: java.util Part 1: The Collections Framework 473<br /> ts.add("B");<br /> ts.add("E");<br /> ts.add("F");<br /> ts.add("D");<br /> // Get an iterator<br /> Iterator i = ts.iterator();<br /> }<br /> }<br /> // Display elements<br /> while(i.hasNext()) {<br /> Object element = i.next();<br /> System.out.print(element + " ");<br /> }<br /> System.out.println();<br /> As the following output shows, the tree is now stored in reverse order:<br /> F E D C B A<br /> Look closely at the MyComp class, which implements Comparator and overrides<br /> compare( ). (As explained earlier, overriding equals( ) is neither necessary nor<br /> common.) Inside compare( ), the String method compareTo( ) compares the two<br /> strings. However, bStr—not aStr—invokes compareTo( ). This causes the outcome of<br /> the comparison to be reversed.<br /> For a more practical example, the following program is an updated version of<br /> the TreeMap program shown earlier that stores account balances. In the previous<br /> version, the accounts were sorted by name, but the sorting began with the first name.<br /> The following program sorts the accounts by last name. To do so, it uses a comparator<br /> that compares the last name of each account. This results in the map being sorted by<br /> last name.<br /> // Use a comparator to sort accounts by last name.<br /> import java.util.*;<br /> // Compare last whole words in two strings.<br /> class TComp implements Comparator {<br /> public int compare(Object a, Object b) {<br /> int i, j, k;<br /> String aStr, bStr;</div> <div>THE JAVA LIBRARY<br /> Chapter 19: The Applet Class 647<br /> Improving the Banner Applet<br /> It is possible to use a parameter to enhance the banner applet shown earlier. In the<br /> previous version, the message being scrolled was hard-coded into the applet. However,<br /> passing the message as a parameter allows the banner applet to display a different<br /> message each time it is executed. This improved version is shown here. Notice that the<br /> APPLET tag at the top of the file now specifies a parameter called message that is linked<br /> to a quoted string.<br /> // A parameterized banner<br /> import java.awt.*;<br /> import java.applet.*;<br /> /*<br /> <applet code="ParamBanner" width=300 height=50><br /> <param name=message value="Java makes the Web move!"><br /> </applet><br /> */<br /> public class ParamBanner extends Applet implements Runnable {<br /> String msg;<br /> Thread t = null;<br /> int state;<br /> boolean stopFlag;<br /> // Set colors and initialize thread.<br /> public void init() {<br /> setBackground(Color.cyan);<br /> setForeground(Color.red);<br /> }<br /> // Start thread<br /> public void start() {<br /> msg = getParameter("message");<br /> if(msg == null) msg = "Message not found.";<br /> msg = " " + msg;<br /> t = new Thread(this);<br /> stopFlag = false;<br /> t.start();<br /> }<br /> // Entry point for the thread that runs the banner.<br /> public void run() {</div> <div>THE JAVA LIBRARY<br /> Chapter 18: Networking 617<br /> MimeHeader inmh) {<br /> try {<br /> int start = url.indexOf("://") + 3;<br /> int path = url.indexOf('/', start);<br /> String site = url.substring(start, path).toLowerCase();<br /> int port = 80;<br /> String server_url = url.substring(path);<br /> int colon = site.indexOf(':');<br /> if (colon > 0) {<br /> port = Integer.parseInt(site.substring(colon + 1));<br /> site = site.substring(0, colon);<br /> }<br /> url = "/cache/" + site + ((port != 80) ? (":" + port) : "") +<br /> server_url;<br /> if (url.endsWith("/"))<br /> url += indexfile;<br /> if (!serveFromCache(out, url)) {<br /> if (readFile(new File(docRoot + url), url) != null) {<br /> serveFromCache(out, url);<br /> return;<br /> }<br /> // If we haven't already cached this page, open a socket<br /> // to the site's port and send a GET command to it.<br /> // We modify the user-agent to add ourselves... "via".<br /> Socket server = new Socket(site, port);<br /> InputStream server_in = server.getInputStream();<br /> OutputStream server_out = server.getOutputStream();<br /> inmh.put("User-Agent", inmh.get("User-Agent") +<br /> " via JavaCompleteReferenceProxy/" + version);<br /> String req = "GET " + server_url + " HTTP/1.0" + CRLF +<br /> inmh + CRLF;<br /> writeString(server_out, req);<br /> String raw_request = getRawRequest(server_in);<br /> HttpResponse server_response =<br /> new HttpResponse(raw_request);<br /> writeString(out, server_response.toString());<br /> if (server_response.statusCode == 200) {<br /> UrlCacheEntry uce = loadFile(server_in, url,<br /> server_response.mh);</div> <div>78 Java™ 2: The Complete Reference<br /> }<br /> }<br /> c += a * b;<br /> c %= 6;<br /> System.out.println("a = " + a);<br /> System.out.println("b = " + b);<br /> System.out.println("c = " + c);<br /> The output of this program is shown here:<br /> a = 6<br /> b = 8<br /> c = 3<br /> Increment and Decrement<br /> The ++ and the – – are Java’s increment and decrement operators. They were introduced<br /> in Chapter 2. Here they will be discussed in detail. As you will see, they have some<br /> special properties that make them quite interesting. Let’s begin by reviewing precisely<br /> what the increment and decrement operators do.<br /> The increment operator increases its operand by one. The decrement operator<br /> decreases its operand by one. For example, this statement:<br /> x = x + 1;<br /> can be rewritten like this by use of the increment operator:<br /> x++;<br /> Similarly, this statement:<br /> x = x - 1;<br /> is equivalent to<br /> x--;</div> <div>This page intentionally left blank.</div> <div>THE JAVA LIBRARY<br /> Chapter 22: Using AWT Controls, Layout Managers, and Menus 753<br /> // add items to os list<br /> os.add("Windows 98/XP");<br /> os.add("Windows NT/2000");<br /> os.add("Solaris");<br /> os.add("MacOS");<br /> // add items to browser list<br /> browser.add("Netscape 3.x");<br /> browser.add("Netscape 4.x");<br /> browser.add("Netscape 5.x");<br /> browser.add("Netscape 6.x");<br /> }<br /> browser.add("Internet Explorer 4.0");<br /> browser.add("Internet Explorer 5.0");<br /> browser.add("Internet Explorer 6.0");<br /> browser.add("Lynx 2.4");<br /> browser.select(1);<br /> // add lists to window<br /> add(os);<br /> add(browser);<br /> // register to receive action events<br /> os.addActionListener(this);<br /> browser.addActionListener(this);<br /> public void actionPerformed(ActionEvent ae) {<br /> repaint();<br /> }<br /> // Display current selections.<br /> public void paint(Graphics g) {<br /> int idx[];<br /> msg = "Current OS: ";<br /> idx = os.getSelectedIndexes();<br /> for(int i=0; i<idx.length; i++)<br /> msg += os.getItem(idx[i]) + " ";</div> <div>700 Java™ 2: The Complete Reference<br /> // Applet window.<br /> public class WindowEvents extends Applet<br /> implements MouseListener, MouseMotionListener {<br /> SampleFrame f;<br /> String msg = "";<br /> int mouseX=0, mouseY=10;<br /> int movX=0, movY=0;<br /> // Create a frame window.<br /> public void init() {<br /> f = new SampleFrame("Handle Mouse Events");<br /> f.setSize(300, 200);<br /> f.setVisible(true);<br /> }<br /> // register this object to receive its own mouse events<br /> addMouseListener(this);<br /> addMouseMotionListener(this);<br /> // Remove frame window when stopping applet.<br /> public void stop() {<br /> f.setVisible(false);<br /> }<br /> // Show frame window when starting applet.<br /> public void start() {<br /> f.setVisible(true);<br /> }<br /> // Handle mouse clicked.<br /> public void mouseClicked(MouseEvent me) {<br /> }<br /> // Handle mouse entered.<br /> public void mouseEntered(MouseEvent me) {<br /> // save coordinates<br /> mouseX = 0;<br /> mouseY = 24;<br /> msg = "Mouse just entered applet window.";<br /> repaint();</div> <div>Contents<br /> xvii<br /> URL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597<br /> Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 597<br /> URLConnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 599<br /> TCP/IP Server Sockets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 601<br /> A Caching Proxy HTTP Server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602<br /> Source Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 602<br /> Datagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 623<br /> DatagramPacket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624<br /> Datagram Server and Client . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 624<br /> Inet4Address and Inet6Address . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 626<br /> The URI Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 626<br /> 19 The Applet Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627<br /> Applet Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 628<br /> The Applet Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 629<br /> Applet Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632<br /> An Applet Skeleton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632<br /> Applet Initialization and Termination . . . . . . . . . . . . . . . . . . . . . . . 634<br /> Overriding update( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 635<br /> Simple Applet Display Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 636<br /> Requesting Repainting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 638<br /> A Simple Banner Applet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 639<br /> Using the Status Window . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 642<br /> The HTML APPLET Tag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 643<br /> Passing Parameters to Applets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 644<br /> Improving the Banner Applet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 647<br /> getDocumentBase( ) and getCodeBase( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 648<br /> AppletContext and showDocument( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649<br /> The AudioClip Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 651<br /> The AppletStub Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 652<br /> Outputting to the Console . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 652<br /> 20 Event Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653<br /> Two Event Handling Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 654<br /> The Delegation Event Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 654<br /> Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 655<br /> Event Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 655<br /> Event Listeners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 656<br /> Event Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 656<br /> The ActionEvent Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 658<br /> The AdjustmentEvent Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 659<br /> The ComponentEvent Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 660<br /> The ContainerEvent Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 660<br /> The FocusEvent Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 661<br /> The InputEvent Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 661<br /> The ItemEvent Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 662<br /> The KeyEvent Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 663<br /> The MouseEvent Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 664</div> <div>288 Java™ 2: The Complete Reference<br /> ob2.t.join();<br /> ob3.t.join();<br /> } catch (InterruptedException e) {<br /> System.out.println("Main thread Interrupted");<br /> }<br /> System.out.println("Thread One is alive: "<br /> + ob1.t.isAlive());<br /> System.out.println("Thread Two is alive: "<br /> + ob2.t.isAlive());<br /> System.out.println("Thread Three is alive: "<br /> + ob3.t.isAlive());<br /> }<br /> }<br /> System.out.println("Main thread exiting.");<br /> Sample output from this program is shown here:<br /> New thread: Thread[One,5,main]<br /> New thread: Thread[Two,5,main]<br /> New thread: Thread[Three,5,main]<br /> Thread One is alive: true<br /> Thread Two is alive: true<br /> Thread Three is alive: true<br /> Waiting for threads to finish.<br /> One: 5<br /> Two: 5<br /> Three: 5<br /> One: 4<br /> Two: 4<br /> Three: 4<br /> One: 3<br /> Two: 3<br /> Three: 3<br /> One: 2<br /> Two: 2<br /> Three: 2<br /> One: 1<br /> Two: 1<br /> Three: 1</div> <div>Chapter 9<br /> Packages and<br /> Interfaces<br /> 223</div> <div>THE JAVA LANGUAGE<br /> Chapter 11: Multithreaded Programming 279<br /> prints a message if it gets interrupted. In a real program, you would need to handle<br /> this differently. Here is the output generated by this program:<br /> Current thread: Thread[main,5,main]<br /> After name change: Thread[My Thread,5,main]<br /> 5<br /> 4<br /> 3<br /> 2<br /> 1<br /> Notice the output produced when t is used as an argument to println( ). This displays,<br /> in order: the name of the thread, its priority, and the name of its group. By default, the<br /> name of the main thread is main. Its priority is 5, which is the default value, and main<br /> is also the name of the group of threads to which this thread belongs. A thread group is<br /> a data structure that controls the state of a collection of threads as a whole. This process<br /> is managed by the particular run-time environment and is not discussed in detail here.<br /> After the name of the thread is changed, t is again output. This time, the new name of<br /> the thread is displayed.<br /> Let’s look more closely at the methods defined by Thread that are used in the<br /> program. The sleep( ) method causes the thread from which it is called to suspend<br /> execution for the specified period of milliseconds. Its general form is shown here:<br /> static void sleep(long milliseconds) throws InterruptedException<br /> The number of milliseconds to suspend is specified in milliseconds. This method may<br /> throw an InterruptedException.<br /> The sleep( ) method has a second form, shown next, which allows you to specify<br /> the period in terms of milliseconds and nanoseconds:<br /> static void sleep(long milliseconds, int nanoseconds) throws InterruptedException<br /> This second form is useful only in environments that allow timing periods as short<br /> as nanoseconds.<br /> As the preceding program shows, you can set the name of a thread by using<br /> setName( ). You can obtain the name of a thread by calling getName( ) (but note<br /> that this procedure is not shown in the program). These methods are members<br /> of the Thread class and are declared like this:<br /> final void setName(String threadName)<br /> final String getName( )<br /> Here, threadName specifies the name of the thread.</div> <div>986 Java™ 2: The Complete Reference<br /> Additionally, many of the standard library functions supported by C++ are<br /> holdovers from C. When one of these C-based functions requires the address<br /> of an argument, a pointer to the argument is used. Inside the function, the<br /> argument is then accessed through its pointer.<br /> ■ To provide a more efficient means of implementing certain constructs—<br /> especially array indexing. For example, it is often more efficient to sequentially<br /> move through an array using a pointer rather than an array index. While modern<br /> compilers implement highly efficient optimizations, pointers can still provide a<br /> significant performance boost. Thus, the use of pointers to access arrays is<br /> ubiquitous in C++ code.<br /> ■ To support memory allocation. In C++, when you allocate memory, an<br /> address (that is, a pointer) to that memory is returned. This address must be<br /> assigned to a pointer variable. Once this has been done, the pointer can point to<br /> any part of the allocated memory—or anywhere else, for that matter—by means<br /> of pointer arithmetic. In Java, when an object is allocated by new, a reference to<br /> the object is returned. This reference must be assigned to a reference variable of<br /> a compatible type. While Java reference variables do implicitly point to the<br /> object that was allocated by the new operator, they cannot be manipulated in<br /> the same way as C++ pointers. And they cannot point to memory outside of the<br /> Java run-time context.<br /> ■ To provide access to any arbitrary machine address, possibly to call a ROM<br /> routine or to read/write directly to memory. Since Java purposely disallows<br /> such actions, this use of pointers has no direct parallel. If you are writing<br /> applications, not applets, you can always use Java’s native capabilities<br /> (described in Part One) to gain access to native code routines that would<br /> be allowed access to such system resources.<br /> Let’s look at two situations in which pointer-based C++ code is converted to Java.<br /> Converting Pointer Parameters<br /> For the most part, it is quite easy to convert a C++ function that uses pointer<br /> parameters into its equivalent Java method. Since Java passes all objects by reference,<br /> sometimes the conversion simply requires the removal of C++’s pointer operators. For<br /> example, consider this C++ program that reverses the signs of a Coord object, which<br /> stores a pair of Cartesian coordinates. The function reverseSign( ) is passed a pointer</div> <div>THE JAVA LIBRARY<br /> Chapter 21: Introducing the AWT: Working with Windows, Graphics, and Text 729<br /> // Demonstrate text alignment.<br /> import java.applet.*;<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import java.util.*;<br /> /* <title>Text Layout</title><br /> <applet code="TextLayout" width=200 height=200><br /> <param name="text" value="Output to a Java window is actually<br /> quite easy.<br /> As you have seen, the AWT provides support for<br /> fonts, colors, text, and graphics. <P> Of course,<br /> you must effectively utilize these items<br /> if you are to achieve professional results."><br /> <param name="fontname" value="Serif"><br /> <param name="fontSize" value="14"><br /> </applet><br /> */<br /> public class TextLayout extends Applet {<br /> final int LEFT = 0;<br /> final int RIGHT = 1;<br /> final int CENTER = 2;<br /> final int LEFTRIGHT =3;<br /> int align;<br /> Dimension d;<br /> Font f;<br /> FontMetrics fm;<br /> int fontSize;<br /> int fh, bl;<br /> int space;</div> <div>THE JAVA LIBRARY<br /> Chapter 15: java.util Part 1: The Collections Framework 489<br /> v.addElement(new Integer(1));<br /> v.addElement(new Integer(2));<br /> v.addElement(new Integer(3));<br /> v.addElement(new Integer(4));<br /> System.out.println("Capacity after four additions: " +<br /> v.capacity());<br /> v.addElement(new Double(5.45));<br /> System.out.println("Current capacity: " +<br /> v.capacity());<br /> v.addElement(new Double(6.08));<br /> v.addElement(new Integer(7));<br /> System.out.println("Current capacity: " +<br /> v.capacity());<br /> v.addElement(new Float(9.4));<br /> v.addElement(new Integer(10));<br /> System.out.println("Current capacity: " +<br /> v.capacity());<br /> v.addElement(new Integer(11));<br /> v.addElement(new Integer(12));<br /> System.out.println("First element: " +<br /> (Integer)v.firstElement());<br /> System.out.println("Last element: " +<br /> (Integer)v.lastElement());<br /> if(v.contains(new Integer(3)))<br /> System.out.println("Vector contains 3.");<br /> // enumerate the elements in the vector.<br /> Enumeration vEnum = v.elements();<br /> }<br /> }<br /> System.out.println("\nElements in vector:");<br /> while(vEnum.hasMoreElements())<br /> System.out.print(vEnum.nextElement() + " ");<br /> System.out.println();</div> <div>APPLYING JAVA<br /> Chapter 32: Scrabblet: A Multiplayer Word Game 1115<br /> hit( )<br /> The hit( ) method returns true if the xp,yp pair passed in falls inside the bounds of<br /> this Letter.<br /> boolean hit(int xp, int yp) {<br /> return (xp >= x && xp < x + w && yp >= y && yp < y + h);<br /> }<br /> validate( )<br /> The validate( ) method is used to load the fonts to find out how big the letters are,<br /> to decide where to paint them. This information is cached in the private variables<br /> discussed earlier. The results of these calculations are used next in paint( ).<br /> private int font_ascent;<br /> void validate(Graphics g) {<br /> FontMetrics fm;<br /> if (h != lasth) {<br /> font = new Font("SansSerif", Font.BOLD, (int)(h * .6));<br /> g.setFont(font);<br /> fm = g.getFontMetrics();<br /> font_ascent = fm.getAscent();<br /> y0 = (h - font_ascent) * 4 / 10 + font_ascent;<br /> smfont = new Font("SansSerif", Font.BOLD, (int)(h * .3));<br /> g.setFont(smfont);<br /> fm = g.getFontMetrics();<br /> ys0 = y0 + fm.getAscent() / 2;<br /> lasth = h;<br /> }<br /> if (!valid) {<br /> valid = true;<br /> g.setFont(font);<br /> fm = g.getFontMetrics();<br /> w0 = fm.stringWidth(symbol);<br /> g.setFont(smfont);<br /> fm = g.getFontMetrics();<br /> ws0 = fm.stringWidth("" + points);<br /> int slop = w - (w0 + gap + ws0);<br /> x0 = slop / 2;<br /> if (x0 < 1)</div> <div>336 Java™ 2: The Complete Reference<br /> However, because Java programs are compiled to bytecode, which is then interpreted<br /> (or compiled on-the-fly) by the Java run-time system, it would seem impossible to call<br /> a native code subroutine from within your Java program. Fortunately, this conclusion<br /> is false. Java provides the native keyword, which is used to declare native code methods.<br /> Once declared, these methods can be called from inside your Java program just as you<br /> call any other Java method.<br /> To declare a native method, precede the method with the native modifier, but do<br /> not define any body for the method. For example:<br /> public native int meth() ;<br /> After you declare a native method, you must write the native method and follow a<br /> rather complex series of steps to link it with your Java code.<br /> Most native methods are written in C. The mechanism used to integrate C code<br /> with a Java program is called the Java Native Interface (JNI). This methodology was<br /> created by Java 1.1 and then expanded and enhanced by Java 2. (Java 1.0 used a<br /> different approach, which is now completely outdated.) A detailed description of the<br /> JNI is beyond the scope of this book, but the following description provides sufficient<br /> information for most applications.<br /> The precise steps that you need to follow will vary between different Java environments<br /> and versions. This also depends on the language that you are using to implement the<br /> native method. The following discussion assumes a Windows 95/98/XP/NT/2000<br /> environment. The language used to implement the native method is C.<br /> The easiest way to understand the process is to work through an example. To<br /> begin, enter the following short program, which uses a native method called test( ):<br /> // A simple example that uses a native method.<br /> public class NativeDemo {<br /> int i;<br /> public static void main(String args[]) {<br /> NativeDemo ob = new NativeDemo();<br /> }<br /> ob.i = 10;<br /> System.out.println("This is ob.i before the native method:" +<br /> ob.i);<br /> ob.test(); // call a native method<br /> System.out.println("This is ob.i after the native method:" +<br /> ob.i);</div> <div>THE JAVA LANGUAGE<br /> Chapter 3: Data Types, Variables, and Arrays 71<br /> of type String can be assigned to another variable of type String. You can use an object of<br /> type String as an argument to println( ). For example, consider the following fragment:<br /> String str = "this is a test";<br /> System.out.println(str);<br /> Here, str is an object of type String. It is assigned the string “this is a test”. This string<br /> is displayed by the println( ) statement.<br /> As you will see later, String objects have many special features and attributes that<br /> make them quite powerful and easy to use. However, for the next few chapters, you<br /> will be using them only in their simplest form.<br /> A Note to C/C++ Programmers About Pointers<br /> If you are an experienced C/C++ programmer, then you know that these languages<br /> provide support for pointers. However, no mention of pointers has been made in this<br /> chapter. The reason for this is simple: Java does not support or allow pointers. (Or<br /> more properly, Java does not support pointers that can be accessed and/or modified<br /> by the programmer.) Java cannot allow pointers, because doing so would allow Java<br /> applets to breach the firewall between the Java execution environment and the host<br /> computer. (Remember, a pointer can be given any address in memory—even addresses<br /> that might be outside the Java run-time system.) Since C/C++ make extensive use of<br /> pointers, you might be thinking that their loss is a significant disadvantage to Java.<br /> However, this is not true. Java is designed in such a way that as long as you stay within<br /> the confines of the execution environment, you will never need to use a pointer, nor would<br /> there be any benefit in using one. For tips on converting C/C++ code to Java, including<br /> pointers, see Chapter 29.</div> <div>THE JAVA LANGUAGE<br /> Chapter 6: Introducing Classes 151<br /> called finalization. By using finalization, you can define specific actions that will occur<br /> when an object is just about to be reclaimed by the garbage collector.<br /> To add a finalizer to a class, you simply define the finalize( ) method. The Java run<br /> time calls that method whenever it is about to recycle an object of that class. Inside the<br /> finalize( ) method you will specify those actions that must be performed before an<br /> object is destroyed. The garbage collector runs periodically, checking for objects that<br /> are no longer referenced by any running state or indirectly through other referenced<br /> objects. Right before an asset is freed, the Java run time calls the finalize( ) method on<br /> the object.<br /> The finalize( ) method has this general form:<br /> protected void finalize( )<br /> {<br /> // finalization code here<br /> }<br /> Here, the keyword protected is a specifier that prevents access to finalize( ) by code<br /> defined outside its class. This and the other access specifiers are explained in Chapter 7.<br /> It is important to understand that finalize( ) is only called just prior to garbage<br /> collection. It is not called when an object goes out-of-scope, for example. This means<br /> that you cannot know when—or even if—finalize( ) will be executed. Therefore, your<br /> program should provide other means of releasing system resources, etc., used by the<br /> object. It must not rely on finalize( ) for normal program operation.<br /> If you are familiar with C++, then you know that C++ allows you to define a destructor<br /> for a class, which is called when an object goes out-of-scope. Java does not support this<br /> idea or provide for destructors. The finalize( ) method only approximates the function<br /> of a destructor. As you get more experienced with Java, you will see that the need for<br /> destructor functions is minimal because of Java’s garbage collection subsystem.<br /> A Stack Class<br /> While the Box class is useful to illustrate the essential elements of a class, it is of little<br /> practical value. To show the real power of classes, this chapter will conclude with<br /> a more sophisticated example. As you recall from the discussion of object-oriented<br /> programming (OOP) presented in Chapter 2, one of OOP’s most important benefits<br /> is the encapsulation of data and the code that manipulates that data. As you have seen,<br /> the class is the mechanism by which encapsulation is achieved in Java. By creating<br /> a class, you are creating a new data type that defines both the nature of the data being<br /> manipulated and the routines used to manipulate it. Further, the methods define a<br /> consistent and controlled interface to the class’ data. Thus, you can use the class<br /> through its methods without having to worry about the details of its implementation</div> <div>THE JAVA LIBRARY<br /> Chapter 22: Using AWT Controls, Layout Managers, and Menus 795<br /> Extending Choice<br /> The following program creates an applet that displays a choice list with items labeled<br /> “Red”, “Green”, and “Blue”. When an entry is selected, a string that contains the name<br /> of the color is displayed on the status line of the applet viewer or browser.<br /> There is one top-level class named ChoiceDemo2 that extends Applet. Its init( )<br /> method creates a choice element and adds it to the applet. MyChoice is an inner class<br /> that extends Choice. It calls enableEvents( ) so that item events may be received by this<br /> object. When an item event is generated, processItemEvent( ) is called. That method<br /> displays a string on the status line and calls processItemEvent( ) for the superclass.<br /> /*<br /> * <applet code=ChoiceDemo2 width=300 height=100><br /> * </applet><br /> */<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import java.applet.*;<br /> public class ChoiceDemo2 extends Applet {<br /> MyChoice choice;<br /> public void init() {<br /> choice = new MyChoice();<br /> choice.add("Red");<br /> choice.add("Green");<br /> choice.add("Blue");<br /> add(choice);<br /> }<br /> class MyChoice extends Choice {<br /> public MyChoice() {<br /> enableEvents(AWTEvent.ITEM_EVENT_MASK);<br /> }<br /> protected void processItemEvent(ItemEvent ie) {<br /> showStatus("Choice selection: " + getSelectedItem());<br /> super.processItemEvent(ie);<br /> }<br /> }<br /> }<br /> Extending List<br /> The following program modifies the preceding example so that it uses a list instead of<br /> a choice menu. There is one top-level class named ListDemo2 that extends Applet. Its<br /> init( ) method creates a list element and adds it to the applet. MyList is an inner class</div> <div>THE JAVA LIBRARY<br /> Chapter 13: String Handling 365<br /> String replace(char original, char replacement)<br /> Here, original specifies the character to be replaced by the character specified by<br /> replacement. The resulting string is returned. For example,<br /> String s = "Hello".replace('l', 'w');<br /> puts the string “Hewwo” into s.<br /> trim( )<br /> The trim( ) method returns a copy of the invoking string from which any leading and<br /> trailing whitespace has been removed. It has this general form:<br /> String trim( )<br /> Here is an example:<br /> String s = " Hello World ".trim();<br /> This puts the string “Hello World” into s.<br /> The trim( ) method is quite useful when you process user commands. For example,<br /> the following program prompts the user for the name of a state and then displays that<br /> state’s capital. It uses trim( ) to remove any leading or trailing whitespace that may<br /> have inadvertently been entered by the user.<br /> // Using trim() to process commands.<br /> import java.io.*;<br /> class UseTrim {<br /> public static void main(String args[])<br /> throws IOException<br /> {<br /> // create a BufferedReader using System.in<br /> BufferedReader br = new<br /> BufferedReader(new InputStreamReader(System.in));<br /> String str;<br /> System.out.println("Enter 'stop' to quit.");<br /> System.out.println("Enter State: ");<br /> do {</div> <div>258 Java™ 2: The Complete Reference<br /> /* If two command-line args are used,<br /> then generate an out-of-bounds exception. */<br /> if(a==2) {<br /> int c[] = { 1 };<br /> c[42] = 99; // generate an out-of-bounds exception<br /> }<br /> } catch(ArrayIndexOutOfBoundsException e) {<br /> System.out.println("Array index out-of-bounds: " + e);<br /> }<br /> }<br /> }<br /> } catch(ArithmeticException e) {<br /> System.out.println("Divide by 0: " + e);<br /> }<br /> As you can see, this program nests one try block within another. The program<br /> works as follows. When you execute the program with no command-line arguments, a<br /> divide-by-zero exception is generated by the outer try block. Execution of the program<br /> by one command-line argument generates a divide-by-zero exception from within the<br /> nested try block. Since the inner block does not catch this exception, it is passed on<br /> to the outer try block, where it is handled. If you execute the program with two<br /> command-line arguments, an array boundary exception is generated from within<br /> the inner try block. Here are sample runs that illustrate each case:<br /> C:\>java NestTry<br /> Divide by 0: java.lang.ArithmeticException: / by zero<br /> C:\>java NestTry One<br /> a = 1<br /> Divide by 0: java.lang.ArithmeticException: / by zero<br /> C:\>java NestTry One Two<br /> a = 2<br /> Array index out-of-bounds:<br /> java.lang.ArrayIndexOutOfBoundsException<br /> Nesting of try statements can occur in less obvious ways when method calls are<br /> involved. For example, you can enclose a call to a method within a try block. Inside<br /> that method is another try statement. In this case, the try within the method is still<br /> nested inside the outer try block, which calls the method. Here is the previous program<br /> recoded so that the nested try block is moved inside the method nesttry( ):</div> <div>732 Java™ 2: The Complete Reference<br /> }<br /> }<br /> }<br /> int nudge = d.width - lineW - (toFill*wc);<br /> int s = fm.stringWidth(" ");<br /> StringTokenizer st = new StringTokenizer(line);<br /> int x = 0;<br /> while(st.hasMoreTokens()) {<br /> String word = st.nextToken();<br /> g.drawString(word, x, y);<br /> if(nudge>0) {<br /> x = x + fm.stringWidth(word) + space + toFill + 1;<br /> nudge--;<br /> } else {<br /> x = x + fm.stringWidth(word) + space + toFill;<br /> }<br /> }<br /> }<br /> break;<br /> class MyMouseAdapter extends MouseAdapter {<br /> TextLayout tl;<br /> public MyMouseAdapter(TextLayout tl) {<br /> this.tl = tl;<br /> }<br /> public void mouseClicked(MouseEvent me) {<br /> tl.align = (tl.align + 1) % 4;<br /> tl.repaint();<br /> }<br /> }<br /> Let’s take a closer look at how this applet works. The applet first creates several<br /> constants that will be used to determine the alignment style, and then declares several<br /> variables. The init( ) method obtains the text that will be displayed. It then initializes<br /> the font size in a try-catch block, which will set the font size to 14 if the fontSize<br /> parameter is missing from the HTML. The text parameter is a long string of text,<br /> with the HTML tag <P> as a paragraph separator.<br /> The update( ) method is the engine for this example. It sets the font and gets the<br /> baseline and font height from a font metrics object. Next, it creates a StringTokenizer<br /> and uses it to retrieve the next token (a string separated by whitespace) from the string<br /> specified by text. If the next token is <P>, it advances the vertical spacing. Otherwise,<br /> update( ) checks to see if the length of this token in the current font will go beyond the</div> <div>154 Java™ 2: The Complete Reference<br /> 1<br /> 0<br /> Stack in mystack2:<br /> 19<br /> 18<br /> 17<br /> 16<br /> 15<br /> 14<br /> 13<br /> 12<br /> 11<br /> 10<br /> As you can see, the contents of each stack are separate.<br /> One last point about the Stack class. As it is currently implemented, it is possible<br /> for the array that holds the stack, stck, to be altered by code outside of the Stack class.<br /> This leaves Stack open to misuse or mischief. In the next chapter, you will see how to<br /> remedy this situation.</div> <div>1076 Java™ 2: The Complete Reference<br /> Figure 32-8.<br /> Herb replies. Notice Patrick’s last message at the bottom<br /> One last word about game play before we get into the source code. The way to win<br /> at this game is to come up with words that score in one direction and also make words<br /> in the other direction. These secondary words tend to be short, two-letter words, but<br /> they add up. In Figure 32-9, Patrick places the Y in DEITY, which will score 21 points<br /> because he gets a face value of 9 doubled to 18, plus he gets to count the word AD,<br /> which runs vertically, for 3 points. Remember that all of the words played with each<br /> turn need to be real words. Eventually, this game will need either an undo for disputed<br /> words or an automatic dictionary checker to resolve conflicts.<br /> The Source Code<br /> Now that you know how to play the game, it is time to examine the source code for the<br /> game. Since several of the classes are quite long, we will sprinkle comments throughout<br /> the code rather than leaving the code till the end.<br /> The APPLET Tag<br /> The APPLET tag for this game is simple. Just name the main class and set the size.<br /> That’s it. There aren’t any <param> tags for Scrabblet. Remember, the bigger you</div> <div>494 Java™ 2: The Complete Reference<br /> The Dictionary class is obsolete. You should implement the Map interface to obtain<br /> key/value storage functionality.<br /> Hashtable<br /> Hashtable was part of the original java.util and is a concrete implementation of a<br /> Dictionary. However, Java 2 reengineered Hashtable so that it also implements the<br /> Map interface. Thus, Hashtable is now integrated into the collections framework. It is<br /> similar to HashMap, but is synchronized.<br /> Like HashMap, Hashtable stores key/value pairs in a hash table. When using a<br /> Hashtable, you specify an object that is used as a key, and the value that you want<br /> linked to that key. The key is then hashed, and the resulting hash code is used as the<br /> index at which the value is stored within the table.<br /> A hash table can only store objects that override the hashCode( ) and equals( )<br /> methods that are defined by Object. The hashCode( ) method must compute and<br /> return the hash code for the object. Of course, equals( ) compares two objects.<br /> Fortunately, many of Java’s built-in classes already implement the hashCode( )<br /> method. For example, the most common type of Hashtable uses a String object as<br /> the key. String implements both hashCode( ) and equals( ).<br /> The Hashtable constructors are shown here:<br /> Hashtable( )<br /> Hashtable(int size)<br /> Hashtable(int size, float fillRatio)<br /> Hashtable(Map m)<br /> The first version is the default constructor. The second version creates a hash table that<br /> has an initial size specified by size. The third version creates a hash table that has an<br /> initial size specified by size and a fill ratio specified by fillRatio. This ratio must be<br /> between 0.0 and 1.0, and it determines how full the hash table can be before it is resized<br /> upward. Specifically, when the number of elements is greater than the capacity of the<br /> hash table multiplied by its fill ratio, the hash table is expanded. If you do not specify<br /> a fill ratio, then 0.75 is used. Finally, the fourth version creates a hash table that is<br /> initialized with the elements in m. The capacity of the hash table is set to twice the<br /> number of elements in m. The default load factor of 0.75 is used. The fourth constructor<br /> was added by Java 2.<br /> In addition to the methods defined by the Map interface, which Hashtable now<br /> implements, Hashtable defines the legacy methods listed in Table 15-13.</div> <div>468 Java™ 2: The Complete Reference<br /> // Get a set of the entries<br /> Set set = hm.entrySet();<br /> // Get an iterator<br /> Iterator i = set.iterator();<br /> // Display elements<br /> while(i.hasNext()) {<br /> Map.Entry me = (Map.Entry)i.next();<br /> System.out.print(me.getKey() + ": ");<br /> System.out.println(me.getValue());<br /> }<br /> System.out.println();<br /> }<br /> }<br /> // Deposit 1000 into John Doe's account<br /> double balance = ((Double)hm.get("John Doe")).doubleValue();<br /> hm.put("John Doe", new Double(balance + 1000));<br /> System.out.println("John Doe's new balance: " +<br /> hm.get("John Doe"));<br /> Output from this program is shown here (the precise order may vary).<br /> Todd Hall: 99.22<br /> Ralph Smith: -19.08<br /> John Doe: 3434.34<br /> Jane Baker: 1378.0<br /> Tom Smith: 123.22<br /> John Doe’s current balance: 4434.34<br /> The program begins by creating a hash map and then adds the mapping of names<br /> to balances. Next, the contents of the map are displayed by using a set-view, obtained<br /> by calling entrySet( ). The keys and values are displayed by calling the getKey( ) and<br /> getValue( ) methods that are defined by Map.Entry. Pay close attention to how the deposit<br /> is made into John Doe’s account. The put( ) method automatically replaces any preexisting<br /> value that is associated with the specified key with the new value. Thus, after John Doe’s<br /> account is updated, the hash map will still contain just one “John Doe” account.<br /> The TreeMap Class<br /> The TreeMap class implements the Map interface by using a tree. A TreeMap provides<br /> an efficient means of storing key/value pairs in sorted order, and allows rapid</div> <div>This page intentionally left blank.</div> <div>402 Java™ 2: The Complete Reference<br /> Void<br /> The Void class has one field, TYPE, which holds a reference to the Class object for type<br /> void. You do not create instances of this class.<br /> Process<br /> The abstract Process class encapsulates a process—that is, an executing program. It is<br /> used primarily as a superclass for the type of objects created by exec( ) in the Runtime<br /> class described in the next section. Process contains the abstract methods shown in<br /> Table 14-9.<br /> Method<br /> void destroy( )<br /> int exitValue( )<br /> InputStream getErrorStream( )<br /> InputStream getInputStream( )<br /> OutputStream getOutputStream( )<br /> int waitFor( )<br /> throws InterruptedException<br /> Description<br /> Terminates the process.<br /> Returns an exit code obtained<br /> from a subprocess.<br /> Returns an input stream that<br /> reads input from the process’ err<br /> output stream.<br /> Returns an input stream that<br /> reads input from the process’ out<br /> output stream.<br /> Returns an output stream that<br /> writes output to the process’ in<br /> input stream.<br /> Returns the exit code returned by<br /> the process. This method does not<br /> return until the process on which<br /> it is called terminates.<br /> Table 14-9.<br /> The Abstract Methods Defined by Process</div> <div>1036 Java™ 2: The Complete Reference<br /> }<br /> }<br /> }<br /> if(fold_offset < 0.0 || fold_offset >= max_fold) {<br /> fold_offset_adder *= -1.0f;<br /> }<br /> Here is what the smash transition looks like before, during, and after:<br /> TearTransition.java<br /> The TearTransition creates the illusion of the current billboard getting torn off the<br /> applet like a piece of paper. It gets ripped upwards and toward the left to reveal the<br /> next billboard image underneath.<br /> There is only one member variable used in this transition, x_cross. It is used as a<br /> multiplier to create the tear effect. The larger the value of this variable, the smaller the<br /> tear effect will appear to be.<br /> The code for this transition has many optimizations. One optimization of<br /> significance is to create the cell frames in reverse order, building the last cell frame first<br /> and the first, last. In their normal order, each subsequent cell frame reveals a little bit<br /> more of the new image underneath. If the frames were to be created in the normal<br /> order, the tear effect would have to be drawn, along with the new image pixels<br /> revealed in the current frame, which had been covered by the tearing effect in the<br /> previous frame. Doing it in reverse only requires redrawing the tearing effect each cell</div> <div>130 Java™ 2: The Complete Reference<br /> The class is at the core of Java. It is the logical construct upon which the entire Java<br /> language is built because it defines the shape and nature of an object. As such,<br /> the class forms the basis for object-oriented programming in Java. Any concept<br /> you wish to implement in a Java program must be encapsulated within a class.<br /> Because the class is so fundamental to Java, this and the next few chapters will be<br /> devoted to it. Here, you will be introduced to the basic elements of a class and learn<br /> how a class can be used to create objects. You will also learn about methods, constructors,<br /> and the this keyword.<br /> Class Fundamentals<br /> Classes have been used since the beginning of this book. However, until now, only the<br /> most rudimentary form of a class has been used. The classes created in the preceding<br /> chapters primarily exist simply to encapsulate the main( ) method, which has been used<br /> to demonstrate the basics of the Java syntax. As you will see, classes are substantially<br /> more powerful than the limited ones presented so far.<br /> Perhaps the most important thing to understand about a class is that it defines a<br /> new data type. Once defined, this new type can be used to create objects of that type.<br /> Thus, a class is a template for an object, and an object is an instance of a class. Because an<br /> object is an instance of a class, you will often see the two words object and instance used<br /> interchangeably.<br /> The General Form of a Class<br /> When you define a class, you declare its exact form and nature. You do this by specifying<br /> the data that it contains and the code that operates on that data. While very simple classes<br /> may contain only code or only data, most real-world classes contain both. As you will<br /> see, a class’ code defines the interface to its data.<br /> A class is declared by use of the class keyword. The classes that have been used up<br /> to this point are actually very limited examples of its complete form. Classes can (and<br /> usually do) get much more complex. The general form of a class definition is shown here:<br /> class classname {<br /> type instance-variable1;<br /> type instance-variable2;<br /> // ...<br /> type instance-variableN;<br /> type methodname1(parameter-list) {<br /> // body of method<br /> }<br /> type methodname2(parameter-list) {<br /> // body of method</div> <div>822 Java™ 2: The Complete Reference<br /> single, larger source image. Loading twenty 2K images takes much longer than loading<br /> a single 40K image that has many frames of an animation tiled into it. If every<br /> subimage is the same size, then you can easily extract these images by using<br /> CropImageFilter to disassemble the block once your applet starts. Here is an example<br /> that creates 16 images taken from a single image. The tiles are then scrambled by<br /> swapping a random pair from the 16 images 32 times.<br /> /*<br /> * <applet code=TileImage.class width=288 height=399><br /> * <param name=img value=picasso.jpg><br /> * </applet><br /> */<br /> import java.applet.*;<br /> import java.awt.*;<br /> import java.awt.image.*;<br /> public class TileImage extends Applet {<br /> Image img;<br /> Image cell[] = new Image[4*4];<br /> int iw, ih;<br /> int tw, th;<br /> public void init() {<br /> try {<br /> img = getImage(getDocumentBase(), getParameter("img"));<br /> MediaTracker t = new MediaTracker(this);<br /> t.addImage(img, 0);<br /> t.waitForID(0);<br /> iw = img.getWidth(null);<br /> ih = img.getHeight(null);<br /> tw = iw / 4;<br /> th = ih / 4;<br /> CropImageFilter f;<br /> FilteredImageSource fis;<br /> t = new MediaTracker(this);<br /> for (int y=0; y<4; y++) {<br /> for (int x=0; x<4; x++) {<br /> f = new CropImageFilter(tw*x, th*y, tw, th);<br /> fis = new FilteredImageSource(img.getSource(), f);<br /> int i = y*4+x;<br /> cell[i] = createImage(fis);<br /> t.addImage(cell[i], i);</div> <div>THE JAVA LIBRARY<br /> Chapter 18: Networking 597<br /> Updated Date: 16-jan-2002<br /> >> Last update of whois database: Thu, 25 Apr 2002 05:05:52 EDT <<<br /> The Registry database contains ONLY .COM, .NET, .ORG, .EDU domains and<br /> Registrars.<br /> URL<br /> That last example was rather obscure, because the modern Internet is not about the<br /> older protocols, like whois, finger, and FTP. It is about WWW, the World Wide Web.<br /> The Web is a loose collection of higher-level protocols and file formats, all unified in a<br /> web browser. One of the most important aspects of the Web is that Tim Berners-Lee<br /> devised a scaleable way to locate all of the resources of the Net. Once you can reliably<br /> name anything and everything, it becomes a very powerful paradigm. The Uniform<br /> Resource Locator (URL) does exactly that.<br /> The URL provides a reasonably intelligible form to uniquely identify or address<br /> information on the Internet. URLs are ubiquitous; every browser uses them to identify<br /> information on the Web. In fact, the Web is really just that same old Internet with all of<br /> its resources addressed as URLs plus HTML. Within Java’s network class library, the<br /> URL class provides a simple, concise API to access information across the Internet<br /> using URLs.<br /> Format<br /> Two examples of URLs are http://www.osborne.com/ and http://www.osborne.com:80/<br /> index.htm. A URL specification is based on four components. The first is the protocol<br /> to use, separated from the rest of the locator by a colon (:). Common protocols are http,<br /> ftp, gopher, and file, although these days almost everything is being done via HTTP (in<br /> fact, most browsers will proceed correctly if you leave off the “http://” from your URL<br /> specification). The second component is the host name or IP address of the host to use;<br /> this is delimited on the left by double slashes (//) and on the right by a slash (/) or<br /> optionally a colon (:). The third component, the port number, is an optional parameter,<br /> delimited on the left from the host name by a colon (:) and on the right by a slash (/).<br /> (It defaults to port 80, the predefined HTTP port; thus “:80” is redundant.) The fourth<br /> part is the actual file path. Most HTTP servers will append a file named index.html<br /> or index.htm to URLs that refer directly to a directory resource. Thus,<br /> http://www.osborne.com/ is the same as http://www.osborne.com/index.htm.<br /> Java’s URL class has several constructors, and each can throw a<br /> MalformedURLException. One commonly used form specifies the URL with a string<br /> that is identical to what you see displayed in a browser:<br /> URL(String urlSpecifier)</div> <div>984 Java™ 2: The Complete Reference<br /> New Features Added by Java<br /> There are a number of features in Java that have no equivalent in C++. Perhaps the<br /> three most important are multithreading, packages, and interfaces, but there are<br /> several others that enrich the Java programming environment as well.<br /> ■ As explained earlier, multithreading allows two or more pieces of the same<br /> program to execute concurrently. Further, this approach to concurrence is<br /> supported at the language level. There is no parallel for this in C++. If you<br /> need to multithread a C++ program, you will need to do so manually, using<br /> operating system functions. While both methods allow for concurrent execution<br /> of two or more threads, Java’s approach is cleaner and easier to use.<br /> ■ There is no feature in C++ that directly corresponds to a Java package. The<br /> closest similarity is a set of library functions that use a common header file.<br /> However, constructing and using a library in C++ is completely different from<br /> constructing and using a package in Java.<br /> ■ The Java interface is somewhat similar to a C++ abstract class. (An abstract class<br /> in C++ is a class that contains at least one pure virtual function.) For example, it<br /> is impossible to create an instance of a C++ abstract class or a Java interface.<br /> Both are used to specify a consistent interface that subclasses will implement.<br /> The main difference is that an interface more cleanly represents this concept.<br /> ■ Java has a streamlined approach to memory allocation. Like C++, it supports<br /> the new keyword. However, it does not have delete. Instead, when the last<br /> reference to an object is destroyed, the object, itself, is automatically deleted the<br /> next time that garbage collection occurs.<br /> ■ Java “removes” the C++ standard library, replacing it with its own set of API<br /> classes. While there is substantial functional similarity, there are significant<br /> differences in the names and parameters. Also, since all of the Java API library<br /> is object-oriented, and only a portion of the C++ library is, there will be<br /> differences in the way library routines are invoked.<br /> ■ The break and continue statements have been enhanced in Java to accept labels<br /> as targets.<br /> ■ The char type in Java declares 16-bit-wide Unicode characters. This makes<br /> them similar to C++’s wchar_t type. The use of Unicode helps ensure<br /> portability.<br /> ■ Java adds the >>> operator, which performs an unsigned right shift.<br /> ■ In addition to supporting single-line and multiline comments, Java adds a third<br /> comment form: the documentation comment. Documentation comments begin<br /> with a /** and end with a */.</div> <div>THE JAVA LIBRARY<br /> Chapter 17: Input/Output: Exploring java.io 571<br /> The first form creates a buffered stream using a buffer with a default size. In the<br /> second, the size of the buffer is passed in bufSize.<br /> PushbackReader<br /> The PushbackReader class allows one or more characters to be returned to the input<br /> stream. This allows you to look ahead in the input stream. Here are its two constructors:<br /> PushbackReader(Reader inputStream)<br /> PushbackReader(Reader inputStream, int bufSize)<br /> The first form creates a buffered stream that allows one character to be pushed back.<br /> In the second, the size of the pushback buffer is passed in bufSize.<br /> PushbackReader provides unread( ), which returns one or more characters to the<br /> invoking input stream. It has the three forms shown here:<br /> void unread(int ch)<br /> void unread(char buffer[ ])<br /> void unread(char buffer[ ], int offset, int numChars)<br /> The first form pushes back the character passed in ch. This will be the next character<br /> returned by a subsequent call to read( ). The second form returns the characters in<br /> buffer. The third form pushes back numChars characters beginning at offset from buffer.<br /> An IOException will be thrown if there is an attempt to return a character when the<br /> pushback buffer is full.<br /> The following program reworks the earlier PushBackInputStream example by<br /> replacing PushBackInputStream with a PushbackReader. As before, it shows how a<br /> programming language parser can use a pushback stream to deal with the difference<br /> between the == operator for comparison and the = operator for assignment.<br /> // Demonstrate unread().<br /> import java.io.*;<br /> class PushbackReaderDemo {<br /> public static void main(String args[]) throws IOException {<br /> String s = "if (a == 4) a = 0;\n";<br /> char buf[] = new char[s.length()];<br /> s.getChars(0, s.length(), buf, 0);<br /> CharArrayReader in = new CharArrayReader(buf);<br /> PushbackReader f = new PushbackReader(in);<br /> int c;</div> <div>THE JAVA LANGUAGE<br /> Chapter 8: Inheritance 207<br /> In the preceding program, the entire class hierarchy, including Box, BoxWeight, and<br /> Shipment, is shown all in one file. This is for your convenience only. In Java, all three<br /> classes could have been placed into their own files and compiled separately. In fact, using<br /> separate files is the norm, not the exception, in creating class hierarchies.<br /> When Constructors Are Called<br /> When a class hierarchy is created, in what order are the constructors for the classes that<br /> make up the hierarchy called? For example, given a subclass called B and a superclass<br /> called A, is A’s constructor called before B’s, or vice versa? The answer is that in a class<br /> hierarchy, constructors are called in order of derivation, from superclass to subclass.<br /> Further, since super( ) must be the first statement executed in a subclass’ constructor,<br /> this order is the same whether or not super( ) is used. If super( ) is not used, then the<br /> default or parameterless constructor of each superclass will be executed. The following<br /> program illustrates when constructors are executed:<br /> // Demonstrate when constructors are called.<br /> // Create a super class.<br /> class A {<br /> A() {<br /> System.out.println("Inside A's constructor.");<br /> }<br /> }<br /> // Create a subclass by extending class A.<br /> class B extends A {<br /> B() {<br /> System.out.println("Inside B's constructor.");<br /> }<br /> }<br /> // Create another subclass by extending B.<br /> class C extends B {<br /> C() {<br /> System.out.println("Inside C's constructor.");<br /> }<br /> }<br /> class CallingCons {<br /> public static void main(String args[]) {</div> <div>638 Java™ 2: The Complete Reference<br /> This applet generates the window shown here:<br /> The methods stop( ) and destroy( ) are not overridden, because they are not needed<br /> by this simple applet.<br /> Requesting Repainting<br /> As a general rule, an applet writes to its window only when its update( ) or paint( )<br /> method is called by the AWT. This raises an interesting question: How can the applet<br /> itself cause its window to be updated when its information changes? For example, if an<br /> applet is displaying a moving banner, what mechanism does the applet use to update<br /> the window each time this banner scrolls? Remember, one of the fundamental<br /> architectural constraints imposed on an applet is that it must quickly return control to<br /> the AWT run-time system. It cannot create a loop inside paint( ) that repeatedly scrolls<br /> the banner, for example. This would prevent control from passing back to the AWT.<br /> Given this constraint, it may seem that output to your applet’s window will be difficult<br /> at best. Fortunately, this is not the case. Whenever your applet needs to update the<br /> information displayed in its window, it simply calls repaint( ).<br /> The repaint( ) method is defined by the AWT. It causes the AWT run-time<br /> system to execute a call to your applet’s update( ) method, which, in its default<br /> implementation, calls paint( ). Thus, for another part of your applet to output to its<br /> window, simply store the output and then call repaint( ). The AWT will then execute<br /> a call to paint( ), which can display the stored information. For example, if part of your<br /> applet needs to output a string, it can store this string in a String variable and then call<br /> repaint( ). Inside paint( ), you will output the string using drawString( ).<br /> The repaint( ) method has four forms. Let’s look at each one, in turn. The simplest<br /> version of repaint( ) is shown here:<br /> void repaint( )<br /> This version causes the entire window to be repainted. The following version<br /> specifies a region that will be repainted:<br /> void repaint(int left, int top, int width, int height)</div> <div>642 Java™ 2: The Complete Reference<br /> Using the Status Window<br /> In addition to displaying information in its window, an applet can also output a<br /> message to the status window of the browser or applet viewer on which it is running.<br /> To do so, call showStatus( ) with the string that you want displayed. The status window<br /> is a good place to give the user feedback about what is occurring in the applet, suggest<br /> options, or possibly report some types of errors. The status window also makes an<br /> excellent debugging aid, because it gives you an easy way to output information about<br /> your applet.<br /> The following applet demonstrates showStatus( ):<br /> // Using the Status Window.<br /> import java.awt.*;<br /> import java.applet.*;<br /> /*<br /> <applet code="StatusWindow" width=300 height=50><br /> </applet><br /> */<br /> public class StatusWindow extends Applet{<br /> public void init() {<br /> setBackground(Color.cyan);<br /> }<br /> }<br /> // Display msg in applet window.<br /> public void paint(Graphics g) {<br /> g.drawString("This is in the applet window.", 10, 20);<br /> showStatus("This is shown in the status window.");<br /> }<br /> Sample output from this program is shown here:</div> <div>xxvi Java™ 2: The Complete Reference<br /> A Book for All Programmers<br /> To use this book does not require any previous programming experience. However,<br /> if you come from a C/C++ background, then you will be able to advance a bit more<br /> rapidly. As most readers will know, Java is similar, in form and spirit, to C/C++. Thus,<br /> knowledge of those langauges helps, but is not necessary. Even if you have never<br /> programmed before, you can learn to program in Java using this book.<br /> What’s Inside<br /> This book covers all aspects of the Java programming language. Part 1 presents an<br /> in-depth tutorial of the Java language. It begins with the basics, including such things<br /> as data types, control statements, and classes. Part 1 also discusses Java’s<br /> exception-handling mechanism, multithreading subsystem, packages, and interfaces.<br /> Part 2 examines the standard Java library. As you will learn, much of Java’s power<br /> is found in its library. Topics include strings, I/O, networking, the standard utilities,<br /> the Collections Framework, applets, GUI-based controls, and imaging.<br /> Part 3 looks at some issues relating to the Java development environment, including<br /> an overview of Java Beans, Servlets, and Swing.<br /> Part 4 presents a number of high-powered Java applets that serve as extended<br /> examples of the way Java can be applied. The final applet, called Scrabblet, is a complete,<br /> multiuser networked game. It shows how to handle some of the toughest issues involved<br /> in Web-based programming.<br /> What’s New in the Fifth Edition<br /> The differences between this and the previous editions of this book mostly involve those<br /> features added by Java 2, version 1.4. Of the many new features found in version 1.4,<br /> perhaps the most important are the assert keyword, the channel-based I/O subsystem,<br /> chained exceptions, and networking enhancements. This fifth edition has been fully<br /> updated to reflect those and other additions. New features are clearly noted in the text,<br /> as are features added by previous releases.<br /> This fifth edition also updates and restores the Sevlets chapter. Previously<br /> this chapter relied upon the now out-dated JSDK (Java Servlets Developers Kit)<br /> to develop and test servlets. It now uses Apache Tomcat, which is the currently<br /> recommended tool.<br /> Don’t Forget: Code on the Web<br /> Remember, the source code for all of the examples and projects in this book is available<br /> free-of-charge on the Web at www.osborne.com.</div> <div>338 Java™ 2: The Complete Reference<br /> * Class: NativeDemo<br /> * Method: test<br /> * Signature: ()V<br /> */<br /> JNIEXPORT void JNICALL Java_NativeDemo_test<br /> (JNIEnv *, jobject);<br /> #ifdef _ _cplusplus<br /> }<br /> #endif<br /> #endif<br /> Pay special attention to the following line, which defines the prototype for the<br /> test( ) function that you will create:<br /> JNIEXPORT void JNICALL Java_NativeDemo_test(JNIEnv *, jobject);<br /> Notice that the name of the function is Java_NativeDemo_test( ). You must use this as the<br /> name of the native function that you implement. That is, instead of creating a C function<br /> called test( ), you will create one called Java_NativeDemo_test( ). The NativeDemo<br /> component of the prefix is added because it identifies the test( ) method as being part of the<br /> NativeDemo class. Remember, another class may define its own native test( ) method that<br /> is completely different from the one declared by NativeDemo. Including the class name in<br /> the prefix provides a way to differentiate between differing versions. As a general rule,<br /> native functions will be given a name whose prefix includes the name of the class in which<br /> they are declared.<br /> After producing the necessary header file, you can write your implementation of<br /> test( ) and store it in a file named NativeDemo.c:<br /> /* This file contains the C version of the<br /> test() method.<br /> */<br /> #include <jni.h><br /> #include "NativeDemo.h"<br /> #include <stdio.h><br /> JNIEXPORT void JNICALL Java_NativeDemo_test(JNIEnv *env, jobject obj)<br /> {<br /> jclass cls;<br /> jfieldID fid;<br /> jint i;</div> <div>THE JAVA LANGUAGE<br /> Chapter 6: Introducing Classes 143<br /> int square(int i)<br /> {<br /> return i * i;<br /> }<br /> Now, square( ) will return the square of whatever value it is called with. That is,<br /> square( ) is now a general-purpose method that can compute the square of any integer<br /> value, rather than just 10.<br /> Here is an example:<br /> int x, y;<br /> x = square(5); // x equals 25<br /> x = square(9); // x equals 81<br /> y = 2;<br /> x = square(y); // x equals 4<br /> In the first call to square( ), the value 5 will be passed into parameter i. In the second<br /> call, i will receive the value 9. The third invocation passes the value of y, which is 2 in<br /> this example. As these examples show, square( ) is able to return the square of whatever<br /> data it is passed.<br /> It is important to keep the two terms parameter and argument straight. A parameter<br /> is a variable defined by a method that receives a value when the method is called.<br /> For example, in square( ), i is a parameter. An argument is a value that is passed to<br /> a method when it is invoked. For example, square(100) passes 100 as an argument.<br /> Inside square( ), the parameter i receives that value.<br /> You can use a parameterized method to improve the Box class. In the preceding<br /> examples, the dimensions of each box had to be set separately by use of a sequence<br /> of statements, such as:<br /> mybox1.width = 10;<br /> mybox1.height = 20;<br /> mybox1.depth = 15;<br /> While this code works, it is troubling for two reasons. First, it is clumsy and error prone.<br /> For example, it would be easy to forget to set a dimension. Second, in well-designed<br /> Java programs, instance variables should be accessed only through methods defined by<br /> their class. In the future, you can change the behavior of a method, but you can’t change<br /> the behavior of an exposed instance variable.</div> <div>THE JAVA LANGUAGE<br /> Chapter 5: Control Statements 127<br /> System.out.println("Before the return.");<br /> if(t) return; // return to caller<br /> }<br /> }<br /> System.out.println("This won't execute.");<br /> The output from this program is shown here:<br /> Before the return.<br /> As you can see, the final println( ) statement is not executed. As soon as return is<br /> executed, control passes back to the caller.<br /> One last point: In the preceding program, the if(t) statement is necessary. Without it,<br /> the Java compiler would flag an “unreachable code” error, because the compiler would<br /> know that the last println( ) statement would never be executed. To prevent this error,<br /> the if statement is used here to trick the compiler for the sake of this demonstration.</div> <div>1082 Java™ 2: The Complete Reference<br /> private String getName(String id) {<br /> for (int i = 0; i < idList.getItemCount(); i++) {<br /> String s = idList.getItem(i);<br /> String id1 = s.substring(s.indexOf("(") + 1, s.indexOf(")"));<br /> if (id1.equals(id)) {<br /> return s.substring(s.indexOf(" ") + 3, s.indexOf("@"));<br /> }<br /> }<br /> return null;<br /> }<br /> challenge( )<br /> The challenge( ) method is called by the ServerConnection whenever another player<br /> challenges us to a game. We could have made this method more complicated, so that it<br /> would prompt the user to accept or refuse the challenge, but instead the challenge is<br /> automatically accepted. Notice that the random seed we use to start the game is passed<br /> back to the other player in the accept( ) method. This is used by both sides to initialize<br /> the random state of the tile bag to ensure a synchronous game. We call server.delete( )<br /> to ensure that we are no longer solicited by other players wanting to play against us.<br /> Notice also that we cede the starting turn to the challenger by setting ourturn to false.<br /> // we've been challenged to a game by "id".<br /> void challenge(String id) {<br /> ourturn = false;<br /> int seed = (int)(0x7fffffff * Math.random());<br /> others_name = getName(id); // who was it?<br /> showStatus("challenged by " + others_name);<br /> }<br /> // put some confirmation here...<br /> server.accept(id, seed);<br /> server.delete();<br /> start_Game(seed);<br /> accept( )<br /> accept( ) is the method called on the remote side in response to the server.accept( )<br /> call just mentioned. Just as the other player deleted himself or herself from the list of</div> <div>756 Java™ 2: The Complete Reference<br /> Handling Scroll Bars<br /> To process scroll bar events, you need to implement the AdjustmentListener interface.<br /> Each time a user interacts with a scroll bar, an AdjustmentEvent object is generated.<br /> Its getAdjustmentType( ) method can be used to determine the type of the adjustment.<br /> The types of adjustment events are as follows:<br /> BLOCK_DECREMENT<br /> BLOCK_INCREMENT<br /> TRACK<br /> UNIT_DECREMENT<br /> UNIT_INCREMENT<br /> A page-down event has been generated.<br /> A page-up event has been generated.<br /> An absolute tracking event has been generated.<br /> The line-down button in a scroll bar has been pressed.<br /> The line-up button in a scroll bar has been pressed.<br /> The following example creates both a vertical and a horizontal scroll bar. The<br /> current settings of the scroll bars are displayed. If you drag the mouse while inside<br /> the window, the coordinates of each drag event are used to update the scroll bars.<br /> An asterisk is displayed at the current drag position.<br /> // Demonstrate scroll bars.<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import java.applet.*;<br /> /*<br /> <applet code="SBDemo" width=300 height=200><br /> </applet><br /> */<br /> public class SBDemo extends Applet<br /> implements AdjustmentListener, MouseMotionListener {<br /> String msg = "";<br /> Scrollbar vertSB, horzSB;<br /> public void init() {<br /> int width = Integer.parseInt(getParameter("width"));<br /> int height = Integer.parseInt(getParameter("height"));<br /> vertSB = new Scrollbar(Scrollbar.VERTICAL,<br /> 0, 1, 0, height);<br /> horzSB = new Scrollbar(Scrollbar.HORIZONTAL,<br /> 0, 1, 0, width);</div> <div>952 Java™ 2: The Complete Reference<br /> You can download Tomcat through the Sun Microsystems Web site at java.sun.com.<br /> The current version is 4.0. Follow the instructions to install this toolkit on your<br /> machine. The examples in this chapter assume a Windows environment. The default<br /> location for Tomcat 4.0 is<br /> C:\Program Files\Apache Tomcat 4.0\<br /> This is the location assumed by the examples in this book. If you load Tomcat in a<br /> different location, you will need to make appropriate changes to the examples. You may<br /> need to set the environmental variable JAVA_HOME to the top-level directory in which<br /> the Java Software Development Kit is installed. For Java 2, version 1.4, the default<br /> directory is C:\j2sdk1.4.0, but you will need to confirm this for your environment.<br /> To start Tomcat, select Start Tomcat in the Start | Programs menu, or run startup.bat<br /> from the<br /> C:\Program Files\Apache Tomcat 4.0\bin\<br /> directory. When you are done testing servlets, you can stop Tomcat by selecting Stop<br /> Tomcat in the Start | Programs menu, or run shutdown.bat.<br /> The directory<br /> C:\Program Files\Apache Tomcat 4.0\common\lib\<br /> contains servlet.jar. This JAR file contains the classes and interfaces that are needed<br /> to build servlets. To make this file accessible, update your CLASSPATH environment<br /> variable so that it includes<br /> C:\Program Files\Apache Tomcat 4.0\common\lib\servlet.jar.<br /> Alternatively, you can specify this class file when you compile the servlets. For<br /> example, the following command compiles the first servlet example:<br /> javac HelloServlet.java -classpath "C:\Program Files\Apache Tomcat<br /> 4.0\common\lib\servlet.jar"<br /> Once you have compiled a servlet, you must copy the class file into the directory<br /> that Tomcat uses for example servlet class files. For the purposes of this chapter, you<br /> must put the servlet files into the following directory:<br /> C:\Program Files\Apache Tomcat 4.0\webapps\examples\WEB-INF\classes</div> <div>948 Java™ 2: The Complete Reference<br /> Output from this applet is shown here:<br /> Exploring Swing<br /> As mentioned earlier, Swing is a large system, and it has many features that you will<br /> want to explore on your own. For example, Swing provides toolbars, tooltips, and<br /> progress bars. Also, Swing components can provide a pluggable look and feel, which<br /> means that it is easy to substitute another appearance and behavior for an element.<br /> This can be done dynamically. You may even design your own look and feel. Frankly,<br /> the Swing approach to GUI components might replace the AWT classes some time<br /> in the future, so familiarizing yourself with it now is a good idea.<br /> Swing is just one part of the Java Foundation Classes (JFC). You may want to<br /> explore other JFC features. The Accessibility API can be used to build programs<br /> that are usable by people with disabilities. The Java 2-D API provides advanced<br /> capabilities for working with shapes, text, and images. The Drag-and-Drop API<br /> allows information to be exchanged between Java and non-Java programs.</div> <div>APPLYING JAVA<br /> Chapter 32: Scrabblet: A Multiplayer Word Game 1081<br /> add( )<br /> The add( ) method is called by the ServerConnection whenever a new player enters<br /> the game. We add the player’s name to our List object. Pay special attention to the<br /> formatting of the string in add( ). We use that later to extract certain IDs from the list.<br /> void add(String id, String hostname, String name) {<br /> delete(id); // in case it is already there.<br /> idList.add("(" + id + ") " + name + "@" + hostname);<br /> showStatus("Choose a player from the list");<br /> }<br /> delete( )<br /> The delete( ) method is called when a player no longer wants to be identified as<br /> available for play. This happens when a player quits or decides to play with someone<br /> else. Here, we hunt down the id string in our list by extracting the values inside<br /> parentheses. If there are no more names on the list (and we aren’t playing the game<br /> already: bag == null), then we display a special message telling the user to hang out<br /> until someone comes to make a challenge.<br /> void delete(String id) {<br /> for (int i = 0; i < idList.getItemCount(); i++) {<br /> String s = idList.getItem(i);<br /> s = s.substring(s.indexOf("(") + 1, s.indexOf(")"));<br /> if (s.equals(id)) {<br /> idList.remove(i);<br /> break;<br /> }<br /> }<br /> if (idList.getItemCount() == 0 && bag == null)<br /> showStatus("Wait for other players to arrive.");<br /> }<br /> getName( )<br /> The getName( ) method is very similar to delete( ), except it simply extracts the name<br /> part of the item and returns it. If the id is not found, then null is returned.</div> <div>Contents<br /> ix<br /> Character Literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51<br /> String Literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52<br /> Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52<br /> Declaring a Variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52<br /> Dynamic Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53<br /> The Scope and Lifetime of Variables . . . . . . . . . . . . . . . . . . . . . . . . 54<br /> Type Conversion and Casting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57<br /> Java’s Automatic Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57<br /> Casting Incompatible Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57<br /> Automatic Type Promotion in Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . 59<br /> The Type Promotion Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60<br /> Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61<br /> One-Dimensional Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61<br /> Multidimensional Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64<br /> Alternative Array Declaration Syntax . . . . . . . . . . . . . . . . . . . . . . . 70<br /> A Few Words About Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70<br /> A Note to C/C++ Programmers About Pointers . . . . . . . . . . . . . . . . . . . . . . 71<br /> 4 Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73<br /> Arithmetic Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74<br /> The Basic Arithmetic Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74<br /> The Modulus Operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76<br /> Arithmetic Assignment Operators . . . . . . . . . . . . . . . . . . . . . . . . . . 76<br /> Increment and Decrement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78<br /> The Bitwise Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80<br /> The Bitwise Logical Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82<br /> The Left Shift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84<br /> The Right Shift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86<br /> The Unsigned Right Shift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87<br /> Bitwise Operator Assignments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89<br /> Relational Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90<br /> Boolean Logical Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92<br /> Short-Circuit Logical Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93<br /> The Assignment Operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94<br /> The ? Operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95<br /> Operator Precedence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96<br /> Using Parentheses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96<br /> 5 Control Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99<br /> Java’s Selection Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100<br /> if . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100<br /> switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104<br /> Iteration Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109<br /> while . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109<br /> do-while . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111<br /> for . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114<br /> Some for Loop Variations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117<br /> Nested Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119</div> <div>20 Java™ 2: The Complete Reference<br /> manufacturers can implement one in any way they please. However, from the driver’s<br /> point of view, they all work the same. This same idea can be applied to programming.<br /> The power of encapsulated code is that everyone knows how to access it and thus<br /> can use it regardless of the implementation details—and without fear of unexpected<br /> side effects.<br /> In Java the basis of encapsulation is the class. Although the class will be examined<br /> in great detail later in this book, the following brief discussion will be helpful now. A<br /> class defines the structure and behavior (data and code) that will be shared by a set of<br /> objects. Each object of a given class contains the structure and behavior defined by the<br /> class, as if it were stamped out by a mold in the shape of the class. For this reason, objects<br /> are sometimes referred to as instances of a class. Thus, a class is a logical construct; an<br /> object has physical reality.<br /> When you create a class, you will specify the code and data that constitute that<br /> class. Collectively, these elements are called members of the class. Specifically, the data<br /> defined by the class are referred to as member variables or instance variables. The code<br /> that operates on that data is referred to as member methods or just methods. (If you are<br /> familiar with C/C++, it may help to know that what a Java programmer calls a method,<br /> a C/C++ programmer calls a function.) In properly written Java programs, the methods<br /> define how the member variables can be used. This means that the behavior and interface<br /> of a class are defined by the methods that operate on its instance data.<br /> Since the purpose of a class is to encapsulate complexity, there are mechanisms for<br /> hiding the complexity of the implementation inside the class. Each method or variable<br /> in a class may be marked private or public. The public interface of a class represents<br /> everything that external users of the class need to know, or may know. The private<br /> methods and data can only be accessed by code that is a member of the class. Therefore,<br /> any other code that is not a member of the class cannot access a private method or variable.<br /> Since the private members of a class may only be accessed by other parts of your program<br /> through the class’ public methods, you can ensure that no improper actions take place.<br /> Of course, this means that the public interface should be carefully designed not to expose<br /> too much of the inner workings of a class (see Figure 2-1).<br /> Inheritance<br /> Inheritance is the process by which one object acquires the properties of another object.<br /> This is important because it supports the concept of hierarchical classification. As<br /> mentioned earlier, most knowledge is made manageable by hierarchical (that is, top-down)<br /> classifications. For example, a Golden Retriever is part of the classification dog, which<br /> in turn is part of the mammal class, which is under the larger class animal. Without the<br /> use of hierarchies, each object would need to define all of its characteristics explicitly.<br /> However, by use of inheritance, an object need only define those qualities that make it<br /> unique within its class. It can inherit its general attributes from its parent. Thus, it is the<br /> inheritance mechanism that makes it possible for one object to be a specific instance of<br /> a more general case. Let’s take a closer look at this process.</div> <div>THE JAVA LANGUAGE<br /> Chapter 12: I/O, Applets, and Other Topics 341<br /> Here is an example that uses assert. It verifies that the return value of getnum( )<br /> is positive.<br /> // Demonstrate assert.<br /> class AssertDemo {<br /> static int val = 3;<br /> // Return an integer.<br /> static int getnum() {<br /> return val--;<br /> }<br /> public static void main(String args[])<br /> {<br /> int n;<br /> for(int i=0; i < 10; i++) {<br /> n = getnum();<br /> assert n > 0; // will fail when n is 0<br /> }<br /> }<br /> }<br /> System.out.println("n is " + n);<br /> Programs that use assert must be compiled using the -source 1.4 option. For example,<br /> to compile the preceding program, use this line:<br /> javac -source 1.4 AssertDemo.java<br /> To enable assertion checking at run time, you must specify the -ea option. For example,<br /> to enable assertions for AssertDemo, execute it using this line.<br /> java -ea AssertDemo<br /> After compiling and running as just described, the program creates the following<br /> output.<br /> n is 3<br /> n is 2<br /> n is 1</div> <div>708 Java™ 2: The Complete Reference<br /> Drawing Ellipses and Circles<br /> To draw an ellipse, use drawOval( ). To fill an ellipse, use fillOval( ). These methods<br /> are shown here:<br /> void drawOval(int top, int left, int width, int height)<br /> void fillOval(int top, int left, int width, int height)<br /> The ellipse is drawn within a bounding rectangle whose upper-left corner is specified<br /> by top,left and whose width and height are specified by width and height.<br /> To draw a circle, specify a square as the bounding rectangle.<br /> The following program draws several ellipses:<br /> // Draw Ellipses<br /> import java.awt.*;<br /> import java.applet.*;<br /> /*<br /> <applet code="Ellipses" width=300 height=200><br /> </applet><br /> */<br /> public class Ellipses extends Applet {<br /> public void paint(Graphics g) {<br /> g.drawOval(10, 10, 50, 50);<br /> g.fillOval(100, 10, 75, 50);<br /> g.drawOval(190, 10, 90, 30);<br /> g.fillOval(70, 90, 140, 100);<br /> }<br /> }<br /> Sample output from this program is shown here:</div> <div>38 Java™ 2: The Complete Reference<br /> Comments<br /> As mentioned, there are three types of comments defined by Java. You have already<br /> seen two: single-line and multiline. The third type is called a documentation comment.<br /> This type of comment is used to produce an HTML file that documents your program.<br /> The documentation comment begins with a /** and ends with a */. Documentation<br /> comments are explained in Appendix A.<br /> Separators<br /> In Java, there are a few characters that are used as separators. The most commonly<br /> used separator in Java is the semicolon. As you have seen, it is used to terminate<br /> statements. The separators are shown in the following table:<br /> Symbol Name Purpose<br /> ( ) Parentheses Used to contain lists of parameters in method<br /> definition and invocation. Also used for defining<br /> precedence in expressions, containing expressions<br /> in control statements, and surrounding cast types.<br /> { } Braces Used to contain the values of automatically<br /> initialized arrays. Also used to define a block<br /> of code, for classes, methods, and local scopes.<br /> [ ] Brackets Used to declare array types. Also used when<br /> dereferencing array values.<br /> ; Semicolon Terminates statements.<br /> , Comma Separates consecutive identifiers in a variable<br /> declaration. Also used to chain statements together<br /> inside a for statement.<br /> . Period Used to separate package names from subpackages<br /> and classes. Also used to separate a variable or<br /> method from a reference variable.<br /> The Java Keywords<br /> There are 49 reserved keywords currently defined in the Java language (see Table 2-1).<br /> These keywords, combined with the syntax of the operators and separators, form the<br /> definition of the Java language. These keywords cannot be used as names for a variable,<br /> class, or method.</div> <div>THE JAVA LIBRARY<br /> Chapter 19: The Applet Class 633<br /> need to define all of them. These five methods can be assembled into the skeleton<br /> shown here:<br /> // An Applet skeleton.<br /> import java.awt.*;<br /> import java.applet.*;<br /> /*<br /> <applet code="AppletSkel" width=300 height=100><br /> </applet><br /> */<br /> public class AppletSkel extends Applet {<br /> // Called first.<br /> public void init() {<br /> // initialization<br /> }<br /> }<br /> /* Called second, after init(). Also called whenever<br /> the applet is restarted. */<br /> public void start() {<br /> // start or resume execution<br /> }<br /> // Called when the applet is stopped.<br /> public void stop() {<br /> // suspends execution<br /> }<br /> /* Called when applet is terminated. This is the last<br /> method executed. */<br /> public void destroy() {<br /> // perform shutdown activities<br /> }<br /> // Called when an applet's window must be restored.<br /> public void paint(Graphics g) {<br /> // redisplay contents of window<br /> }<br /> Although this skeleton does not do anything, it can be compiled and run. When run, it<br /> generates the following window when viewed with an applet viewer:</div> <div>308 Java™ 2: The Complete Reference<br /> The Thread class also defines a method called stop( ) that stops a thread. Its signature<br /> is shown here:<br /> final void stop( )<br /> Once a thread has been stopped, it cannot be restarted using resume( ).<br /> Suspending, Resuming, and Stopping Threads Using<br /> Java 2<br /> While the suspend( ), resume( ), and stop( ) methods defined by Thread seem to be a<br /> perfectly reasonable and convenient approach to managing the execution of threads,<br /> they must not be used for new Java programs. Here’s why. The suspend( ) method<br /> of the Thread class is deprecated in Java 2. This was done because suspend( ) can<br /> sometimes cause serious system failures. Assume that a thread has obtained locks on<br /> critical data structures. If that thread is suspended at that point, those locks are not<br /> relinquished. Other threads that may be waiting for those resources can be deadlocked.<br /> The resume( ) method is also deprecated. It does not cause problems, but cannot be<br /> used without the suspend( ) method as its counterpart.<br /> The stop( ) method of the Thread class, too, is deprecated in Java 2. This was done<br /> because this method can sometimes cause serious system failures. Assume that a thread<br /> is writing to a critically important data structure and has completed only part of its<br /> changes. If that thread is stopped at that point, that data structure might be left in a<br /> corrupted state.<br /> Because you can’t use the suspend( ), resume( ),orstop( ) methods in Java 2 to<br /> control a thread, you might be thinking that no way exists to pause, restart, or terminate<br /> a thread. But, fortunately, this is not true. Instead, a thread must be designed so that the<br /> run( ) method periodically checks to determine whether that thread should suspend,<br /> resume, or stop its own execution. Typically, this is accomplished by establishing a flag<br /> variable that indicates the execution state of the thread. As long as this flag is set to<br /> “running,” the run( ) method must continue to let the thread execute. If this variable is<br /> set to “suspend,” the thread must pause. If it is set to “stop,” the thread must terminate.<br /> Of course, a variety of ways exist in which to write such code, but the central theme will<br /> be the same for all programs.<br /> The following example illustrates how the wait( ) and notify( ) methods that are<br /> inherited from Object can be used to control the execution of a thread. This example is<br /> similar to the program in the previous section. However, the deprecated method calls<br /> have been removed. Let us consider the operation of this program.<br /> The NewThread class contains a boolean instance variable named suspendFlag,<br /> which is used to control the execution of the thread. It is initialized to false by the<br /> constructor. The run( ) method contains a synchronized statement block that checks<br /> suspendFlag. If that variable is true, the wait( ) method is invoked to suspend the<br /> execution of the thread. The mysuspend( ) method sets suspendFlag to true. The</div> <div>1090 Java™ 2: The Complete Reference<br /> IntroCanvas.java<br /> The IntroCanvas subclass of Canvas is very simple. It just overrides paint( ) to draw<br /> the name of the applet and a brief copyright notice. It creates some custom colors and<br /> fonts. The display strings are held in static variables simply for clarity.<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> class IntroCanvas extends Canvas {<br /> private Color pink = new Color(255, 200, 200);<br /> private Color blue = new Color(150, 200, 255);<br /> private Color yellow = new Color(250, 220, 100);<br /> private int w, h;<br /> private int edge = 16;<br /> private static final String title = "Scrabblet";<br /> private static final String name =<br /> "Copyright 1999 - Patrick Naughton";<br /> private static final String book =<br /> "Chapter 32 from 'Java: The Complete Reference'";<br /> private Font namefont, titlefont, bookfont;<br /> IntroCanvas() {<br /> setBackground(yellow);<br /> titlefont = new Font("SansSerif", Font.BOLD, 58);<br /> namefont = new Font("SansSerif", Font.BOLD, 18);<br /> bookfont = new Font("SansSerif", Font.PLAIN, 12);<br /> addMouseListener(new MyMouseAdapter());<br /> }<br /> d( )<br /> The private method d( ) is a convenience method that paints centered text with an<br /> optional isometric offset. This is used to give the main title a highlight/shadow effect<br /> by drawing a white string up and to the left by 1, a black string down and to the right<br /> by 1, and then drawing the string one last time in pink, not offset at all.<br /> private void d(Graphics g, String s, Color c, Font f, int y,<br /> int off) {<br /> g.setFont(f);<br /> FontMetrics fm = g.getFontMetrics();<br /> g.setColor(c);</div> <div>APPLYING JAVA<br /> Chapter 31: The Lavatron Applet: A Sports Arena Display 1061<br /> loaded. This is done by passing the result of getImage( ) to MediaTracker’s addImage( )<br /> method, and then calling waitForID( ), which waits until the image is fully loaded<br /> before returning.<br /> To draw the blown-up version of this image, init( ) needs to retrieve the color<br /> information for each pixel in the image. First, it obtains the size of the image, using<br /> getWidth( ) and getHeight( ), saving the width in pixscan. It then assigns pixels to a<br /> new array of pixscan * h integers. Then a PixelGrabber is created. When grabPixels( )<br /> is called, the array is filled in with the color values.<br /> The final step of init( ) is to paint black bulbs on the offscreen image, which makes<br /> the effect more dramatic as the image scrolls from the right side revealing lighted bulbs.<br /> createBulbs( )<br /> The createBulbs( ) method is a helper to init( ). It returns an Image of a stack of bulb<br /> images that can be used to mask out a column of colored squares to make them look<br /> like lit lightbulbs. It is a little tricky, but quite elegant.<br /> First, it allocates the right number of ints in an array to store the pixels. Then, it<br /> declares another array, which is a picture of a single bulb, represented by the numbers<br /> 0, 1, and 2. The 0s represent black, the 1s transparent pixels, and the 2s represent the<br /> white highlight. Next, a short array is declared—bulbCLUT (bulb Color Look Up Table).<br /> This maps the 0, 1, and 2 just mentioned into full 32-bit pixel values. The 0xff000000 is<br /> opaque black. The high-order byte is alpha, or transparency. The 0x00c0c0c0 is a fully<br /> transparent light gray, and the 0xffffffff is opaque white.<br /> The for loop runs through each pixel, loading the appropriate 0, 1, or 2 from bulbBits<br /> based on the position in the column. This is achieved by use of the mod (%) operator.<br /> This value is then used to look up the color from bulbCLUT. Given this array of pixels,<br /> createBulbs( ) returns the output of createImage( ), passing in a MemoryImageSource<br /> object prepared with the pixels we just constructed.<br /> color( )<br /> The color( ) method returns the color of the pixel at the x,y position in the source image<br /> as a Color object. Since this applet runs continuously, we decided not to simply create<br /> a new Color object each time a single bulb was painted. This would be abusive of the<br /> garbage-collected heap. Instead, unique Color objects are stored in a hash table. The<br /> maximum number of Color objects in the hash table can be as much as the width times<br /> the height of the source image, but in practice, it is usually much less.<br /> update( )<br /> Lavatron overrides update( ) to do nothing, because we don’t want AWT’s implementation<br /> to cause flicker.<br /> paint( )<br /> The paint( ) method is quite simple. The first step calls copyArea( ) to move all of the<br /> columns to the left by one column’s width. Then a for loop is used to fill the rightmost</div> <div>Contents<br /> xiii<br /> Special String Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351<br /> String Literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351<br /> String Concatenation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352<br /> String Concatenation with Other Data Types . . . . . . . . . . . . . . . . . 352<br /> String Conversion and toString( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . 353<br /> Character Extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355<br /> charAt( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355<br /> getChars( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355<br /> getBytes( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356<br /> toCharArray( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356<br /> String Comparison . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356<br /> equals( ) and equalsIgnoreCase( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . 357<br /> regionMatches( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358<br /> startsWith( ) and endsWith( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358<br /> equals( ) Versus == . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359<br /> compareTo( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359<br /> Searching Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361<br /> Modifying a String . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363<br /> substring( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363<br /> concat( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364<br /> replace( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364<br /> trim( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365<br /> Data Conversion Using valueOf( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366<br /> Changing the Case of Characters Within a String . . . . . . . . . . . . . . . . . . . . . 367<br /> String Methods Added by Java 2, Version 1.4 . . . . . . . . . . . . . . . . . . . . . . . . 368<br /> StringBuffer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369<br /> StringBuffer Constructors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369<br /> length( ) and capacity( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369<br /> ensureCapacity( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370<br /> setLength( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370<br /> charAt( ) and setCharAt( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371<br /> getChars( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371<br /> append( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372<br /> insert( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373<br /> reverse( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373<br /> delete( ) and deleteCharAt( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374<br /> replace( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375<br /> substring( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375<br /> StringBuffer Methods Added by Java 2, Version 1.4 . . . . . . . . . . . 376<br /> 14 Exploring java.lang . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379<br /> Simple Type Wrappers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380<br /> Number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381<br /> Double and Float . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381<br /> Byte, Short, Integer, and Long . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387<br /> Character . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397<br /> Boolean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401<br /> Void . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402<br /> Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402</div> <div>Chapter 4<br /> Operators<br /> 73</div> <div>654 Java™ 2: The Complete Reference<br /> This chapter examines an important aspect of Java that relates to applets: events. As<br /> explained in Chapter 19, applets are event-driven programs. Thus, event handling<br /> is at the core of successful applet programming. Most events to which your applet<br /> will respond are generated by the user. These events are passed to your applet in a variety<br /> of ways, with the specific method depending upon the actual event. There are several<br /> types of events. The most commonly handled events are those generated by the mouse,<br /> the keyboard, and various controls, such as a push button. Events are supported by the<br /> java.awt.event package.<br /> The chapter begins with an overview of Java’s event handling mechanism. It then<br /> examines the main event classes and interfaces, and develops several examples that<br /> demonstrate the fundamentals of event processing. This chapter also explains how to<br /> use adapter classes, inner classes, and anonymous inner classes to streamline event<br /> handling code. The examples provided in the remainder of this book make frequent<br /> use of these techniques.<br /> Two Event Handling Mechanisms<br /> Before beginning our discussion of event handling, an important point must be made:<br /> The way in which events are handled by an applet changed significantly between the<br /> original version of Java (1.0) and modern versions of Java, beginning with version 1.1.<br /> The 1.0 method of event handling is still supported, but it is not recommended for new<br /> programs. Also, many of the methods that support the old 1.0 event model have been<br /> deprecated. The modern approach is the way that events should be handled by all<br /> new programs, including those written for Java 2, and thus is the method employed<br /> by programs in this book.<br /> The Delegation Event Model<br /> The modern approach to handling events is based on the delegation event model, which<br /> defines standard and consistent mechanisms to generate and process events. Its concept<br /> is quite simple: a source generates an event and sends it to one or more listeners.Inthis<br /> scheme, the listener simply waits until it receives an event. Once received, the listener<br /> processes the event and then returns. The advantage of this design is that the application<br /> logic that processes events is cleanly separated from the user interface logic that generates<br /> those events. A user interface element is able to “delegate” the processing of an event to<br /> a separate piece of code.<br /> In the delegation event model, listeners must register with a source in order to receive<br /> an event notification. This provides an important benefit: notifications are sent only to<br /> listeners that want to receive them. This is a more efficient way to handle events than the<br /> design used by the old Java 1.0 approach. Previously, an event was propagated up the<br /> containment hierarchy until it was handled by a component. This required components</div> <div>668 Java™ 2: The Complete Reference<br /> Here, other specifies the opposite window when a focus event occurs. The fromState<br /> specifies the prior state of the window and toState specifies the new state that the<br /> window will have when a window state change occurs.<br /> The most commonly used method in this class is getWindow( ). It returns the<br /> Window object that generated the event. Its general form is shown here:<br /> Window getWindow( )<br /> Java 2, version 1.4, adds methods that return the opposite window (when a focus event<br /> has occurred), the previous window state, and the current window state. These methods<br /> are shown here:<br /> Window getOppositeWindow()<br /> int getOldState()<br /> int getNewState()<br /> Sources of Events<br /> Table 20-2 lists some of the user interface components that can generate the events described<br /> in the previous section. In addition to these graphical user interface elements, other<br /> components, such as an applet, can generate events. For example, you receive key and<br /> mouse events from an applet. (You may also build your own components that generate<br /> events.) In this chapter we will be handling only mouse and keyboard events, but the<br /> following two chapters will be handling events from the sources shown in Table 20-2.<br /> Event Source<br /> Button<br /> Checkbox<br /> Choice<br /> List<br /> Menu Item<br /> Scrollbar<br /> Text components<br /> Window<br /> Description<br /> Generates action events when the button is pressed.<br /> Generates item events when the check box is selected or deselected.<br /> Generates item events when the choice is changed.<br /> Generates action events when an item is double-clicked; generates<br /> item events when an item is selected or deselected.<br /> Generates action events when a menu item is selected; generates item<br /> events when a checkable menu item is selected or deselected.<br /> Generates adjustment events when the scroll bar is manipulated.<br /> Generates text events when the user enters a character.<br /> Generates window events when a window is activated, closed,<br /> deactivated, deiconified, iconified, opened, or quit.<br /> Table 20-2.<br /> Event Source Examples</div> <div>172 Java™ 2: The Complete Reference<br /> [7] 7<br /> [8] 8<br /> [9] 9<br /> Introducing Access Control<br /> As you know, encapsulation links data with the code that manipulates it. However,<br /> encapsulation provides another important attribute: access control. Through<br /> encapsulation, you can control what parts of a program can access the members of a<br /> class. By controlling access, you can prevent misuse. For example, allowing access to<br /> data only through a well-defined set of methods, you can prevent the misuse of that<br /> data. Thus, when correctly implemented, a class creates a “black box” which may be<br /> used, but the inner workings of which are not open to tampering. However, the classes<br /> that were presented earlier do not completely meet this goal. For example, consider the<br /> Stack class shown at the end of Chapter 6. While it is true that the methods push( ) and<br /> pop( ) do provide a controlled interface to the stack, this interface is not enforced. That<br /> is, it is possible for another part of the program to bypass these methods and access the<br /> stack directly. Of course, in the wrong hands, this could lead to trouble. In this section<br /> you will be introduced to the mechanism by which you can precisely control access to<br /> the various members of a class.<br /> How a member can be accessed is determined by the access specifier that modifies its<br /> declaration. Java supplies a rich set of access specifiers. Some aspects of access control<br /> are related mostly to inheritance or packages. (A package is, essentially, a grouping of<br /> classes.) These parts of Java’s access control mechanism will be discussed later. Here,<br /> let’s begin by examining access control as it applies to a single class. Once you<br /> understand the fundamentals of access control, the rest will be easy.<br /> Java’s access specifiers are public, private, and protected. Java also defines a<br /> default access level. protected applies only when inheritance is involved. The other<br /> access specifiers are described next.<br /> Let’s begin by defining public and private. When a member of a class is modified<br /> by the public specifier, then that member can be accessed by any other code. When a<br /> member of a class is specified as private, then that member can only be accessed by<br /> other members of its class. Now you can understand why main( ) has always been<br /> preceded by the public specifier. It is called by code that is outside the program—that<br /> is, by the Java run-time system. When no access specifier is used, then by default the<br /> member of a class is public within its own package, but cannot be accessed outside of<br /> its package. (Packages are discussed in the following chapter.)<br /> In the classes developed so far, all members of a class have used the default access<br /> mode, which is essentially public. However, this is not what you will typically want<br /> to be the case. Usually, you will want to restrict access to the data members of a<br /> class—allowing access only through methods. Also, there will be times when you<br /> will want to define methods which are private to a class.</div> <div>740 Java™ 2: The Complete Reference<br /> pressed. In this version, the label of the button is used to determine which button has<br /> been pressed. The label is obtained by calling the getActionCommand( ) method on the<br /> ActionEvent object passed to actionPerformed( ).<br /> // Demonstrate Buttons<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import java.applet.*;<br /> /*<br /> <applet code="ButtonDemo" width=250 height=150><br /> </applet><br /> */<br /> public class ButtonDemo extends Applet implements ActionListener {<br /> String msg = "";<br /> Button yes, no, maybe;<br /> public void init() {<br /> yes = new Button("Yes");<br /> no = new Button("No");<br /> maybe = new Button("Undecided");<br /> }<br /> add(yes);<br /> add(no);<br /> add(maybe);<br /> yes.addActionListener(this);<br /> no.addActionListener(this);<br /> maybe.addActionListener(this);<br /> public void actionPerformed(ActionEvent ae) {<br /> String str = ae.getActionCommand();<br /> if(str.equals("Yes")) {<br /> msg = "You pressed Yes.";<br /> }<br /> else if(str.equals("No")) {<br /> msg = "You pressed No.";<br /> }<br /> else {<br /> msg = "You pressed Undecided.";<br /> }</div> <div>APPLYING JAVA<br /> Chapter 29: The DynamicBillboard Applet 1013<br /> ■ billboards This parameter specifies the number of billboards you wish to<br /> cycle through.<br /> ■ bill# This is shorthand for bill0, bill1, bill2, and so on, up to one less than the<br /> number of billboards you’ve specified. (Robert is a typical programmer who<br /> starts counting at 0.) You will have as many of these as you specified in the<br /> billboards parameter. The value of each of these bill#s will be a pair of strings<br /> separated by a comma. The first one is the image name to display for this<br /> billboard. The second is the URL of where to go when the user clicks on this<br /> billboard. Here is an example:<br /> <param name="bill0" value="sample.jpg,http://www.example.com/"><br /> ■ transitions This is a list beginning with the number of items in the list as an<br /> integer, followed by the list of Transition subclass names. Here is an example:<br /> <param name="transitions" value="2,TearTransition,SmashTransition"><br /> Here is an example of a complete APPLET tag with all of the transitions discussed<br /> in this chapter:<br /> <applet code=DynamicBillboard width=392 height=72><br /> <param name="bgcolor" value="#ffffff"><br /> <param name="delay" value="5000"><br /> <param name="billboards" value="5"><br /> <param name="bill0"<br /> value="board1.jpg,http://www.someURL"><br /> <param name="bill1"<br /> value="board2.jpg,http://www.someURL"><br /> <param name="bill2"<br /> value="board3.jpg,http://www.someURL"><br /> <param name="bill3"<br /> value="board4.jpg,http://www.someURL"><br /> <param name="bill4"<br /> value="board5.jpg,http://www.someURL"><br /> <param name="transitions"<br /> value="5,ColumnTransition,FadeTransition,TearTransition,<br /> SmashTransition,UnrollTransition"><br /> </applet></div> <div>APPLYING JAVA<br /> Chapter 31: The Lavatron Applet: A Sports Arena Display 1067<br /> }<br /> public final boolean contains(int k) {<br /> return get(k)!=null;<br /> }<br /> public int size() {<br /> return size;<br /> }<br /> public int capacity() {<br /> return capacity;<br /> }<br /> Hot Lava<br /> This applet is another small example of the kind of amazing performance you can<br /> squeeze out of Java if you are careful and diligent. David LaVallée uses many tricks<br /> to avoid excessive memory allocation and unnecessary calls to AWT drawing<br /> functions. Creating the lightbulb mask image from a small array of integers rather<br /> than a loaded GIF image saves download time and increases flexibility. The use of<br /> paint(getGraphics( )) rather than repaint( ) increases frame rate significantly. The<br /> performance gains from using copyArea( ) over rerendering the image or calling<br /> drawImage( ) are profound. Finally, the creation and use of IntHash makes for that<br /> last performance boost by not forcing the system to garbage-collect as often.</div> <div>496 Java™ 2: The Complete Reference<br /> Method<br /> Object remove(Object key)<br /> int size( )<br /> String toString( )<br /> Description<br /> Removes key and its value. Returns the<br /> value associated with key. If key is not in<br /> the hash table, a null object is returned.<br /> Returns the number of entries in the<br /> hash table.<br /> Returns the string equivalent of a<br /> hash table.<br /> Table 15-13.<br /> The Legacy Methods Defined by Hashtable (continued)<br /> The following example reworks the bank account program, shown earlier, so that it<br /> uses a Hashtable to store the names of bank depositors and their current balances:<br /> // Demonstrate a Hashtable<br /> import java.util.*;<br /> class HTDemo {<br /> public static void main(String args[]) {<br /> Hashtable balance = new Hashtable();<br /> Enumeration names;<br /> String str;<br /> double bal;<br /> balance.put("John Doe", new Double(3434.34));<br /> balance.put("Tom Smith", new Double(123.22));<br /> balance.put("Jane Baker", new Double(1378.00));<br /> balance.put("Todd Hall", new Double(99.22));<br /> balance.put("Ralph Smith", new Double(-19.08));<br /> // Show all balances in hash table.<br /> names = balance.keys();<br /> while(names.hasMoreElements()) {<br /> str = (String) names.nextElement();<br /> System.out.println(str + ": " +<br /> balance.get(str));<br /> }<br /> System.out.println();</div> <div>470 Java™ 2: The Complete Reference<br /> System.out.print(me.getKey() + ": ");<br /> System.out.println(me.getValue());<br /> }<br /> System.out.println();<br /> }<br /> }<br /> // Deposit 1000 into John Doe's account<br /> double balance = ((Double)tm.get("John Doe")).doubleValue();<br /> tm.put("John Doe", new Double(balance + 1000));<br /> System.out.println("John Doe's new balance: " +<br /> tm.get("John Doe"));<br /> The following is the output from this program:<br /> Jane Baker: 1378.0<br /> John Doe: 3434.34<br /> Ralph Smith: -19.08<br /> Todd Hall: 99.22<br /> Tom Smith: 123.22<br /> John Doe’s current balance: 4434.34<br /> Notice that TreeMap sorts the keys. However, in this case, they are sorted by first<br /> name instead of last name. You can alter this behavior by specifying a comparator<br /> when the map is created, as described shortly.<br /> The LinkedHashMap Class<br /> Java 2, version 1.4 adds the LinkedHashMap class. This class extends HashMap.<br /> LinkedHashMap maintains a linked list of the entries in the map, in the order in which<br /> they were inserted. This allows insertion-order iteration over the map. That is, when<br /> iterating a LinkedHashMap, the elements will be returned in the order in which they<br /> were inserted. You can also create a LinkedHashMap that returns its elements in the<br /> order in which they were last accessed.<br /> LinkedHashMap defines the following constructors.<br /> LinkedHashMap( )<br /> LinkedHashMap(Map m)<br /> LinkedHashMap(int capacity)<br /> LinkedHashMap(int capacity, float fillRatio)<br /> LinkedHashMap(int capacity, float fillRatio, boolean Order)</div> <div>534 Java™ 2: The Complete Reference<br /> // Demonstrate Timer and TimerTask.<br /> import java.util.*;<br /> class MyTimerTask extends TimerTask {<br /> public void run() {<br /> System.out.println("Timer task executed.");<br /> }<br /> }<br /> class TTest {<br /> public static void main(String args[]) {<br /> MyTimerTask myTask = new MyTimerTask();<br /> Timer myTimer = new Timer();<br /> /* Set an initial delay of 1 second,<br /> then repeat every half second.<br /> */<br /> myTimer.schedule(myTask, 1000, 500);<br /> try {<br /> Thread.sleep(5000);<br /> } catch (InterruptedException exc) {}<br /> }<br /> }<br /> myTimer.cancel();<br /> Currency<br /> Java 2, version 1.4 adds the Currency class. This class encapsulates information about a<br /> currency. It defines no constructors. The methods supported by Currency are shown in<br /> Table 16-10. The following program demonstrates Currency.<br /> // Demonstrate Currency.<br /> import java.util.*;<br /> class CurDemo {<br /> public static void main(String args[]) {<br /> Currency c;</div> <div>THE JAVA LANGUAGE<br /> Chapter 11: Multithreaded Programming 277<br /> have. Java’s messaging system allows a thread to enter a synchronized method on an<br /> object, and then wait there until some other thread explicitly notifies it to come out.<br /> The Thread Class and the Runnable Interface<br /> Java’s multithreading system is built upon the Thread class, its methods, and its<br /> companion interface, Runnable. Thread encapsulates a thread of execution. Since<br /> you can’t directly refer to the ethereal state of a running thread, you will deal with it<br /> through its proxy, the Thread instance that spawned it. To create a new thread, your<br /> program will either extend Thread or implement the Runnable interface.<br /> The Thread class defines several methods that help manage threads. The ones<br /> that will be used in this chapter are shown here:<br /> Method<br /> getName<br /> getPriority<br /> isAlive<br /> join<br /> run<br /> sleep<br /> start<br /> Meaning<br /> Obtain a thread’s name.<br /> Obtain a thread’s priority.<br /> Determine if a thread is still running.<br /> Wait for a thread to terminate.<br /> Entry point for the thread.<br /> Suspend a thread for a period of time.<br /> Start a thread by calling its run method.<br /> Thus far, all the examples in this book have used a single thread of execution. The<br /> remainder of this chapter explains how to use Thread and Runnable to create and<br /> manage threads, beginning with the one thread that all Java programs have: the<br /> main thread.<br /> The Main Thread<br /> When a Java program starts up, one thread begins running immediately. This is<br /> usually called the main thread of your program, because it is the one that is executed<br /> when your program begins. The main thread is important for two reasons:<br /> ■ It is the thread from which other “child” threads will be spawned.<br /> ■ Often it must be the last thread to finish execution because it performs various<br /> shutdown actions.</div> <div>THE JAVA LIBRARY<br /> Chapter 15: java.util Part 1: The Collections Framework 491<br /> Method<br /> boolean empty( )<br /> Object peek( )<br /> Object pop( )<br /> Object push(Object element)<br /> int search(Object element)<br /> Description<br /> Returns true if the stack is empty, and returns false<br /> if the stack contains elements.<br /> Returns the element on the top of the stack, but<br /> does not remove it.<br /> Returns the element on the top of the stack,<br /> removing it in the process.<br /> Pushes element onto the stack. element is also<br /> returned.<br /> Searches for element in the stack. If found, its offset<br /> from the top of the stack is returned. Otherwise, –1<br /> is returned.<br /> Table 15-11.<br /> The Methods Defined by Stack<br /> are required to bring it to the top of the stack. Here is an example that creates a stack,<br /> pushes several Integer objects onto it, and then pops them off again:<br /> // Demonstrate the Stack class.<br /> import java.util.*;<br /> class StackDemo {<br /> static void showpush(Stack st, int a) {<br /> st.push(new Integer(a));<br /> System.out.println("push(" + a + ")");<br /> System.out.println("stack: " + st);<br /> }<br /> static void showpop(Stack st) {<br /> System.out.print("pop -> ");<br /> Integer a = (Integer) st.pop();<br /> System.out.println(a);<br /> System.out.println("stack: " + st);<br /> }<br /> public static void main(String args[]) {</div> <div>APPLYING JAVA<br /> Chapter 32: Scrabblet: A Multiplayer Word Game 1099<br /> update( ) and paint( )<br /> Many private variables are declared here to provide easy access to the dimensions of<br /> the board. This code also declares two offscreen buffers, one to be used as the image of<br /> the board and all of the permanently set tiles and another to use as a double buffer for<br /> the display. The update( ) method simply calls paint( ) to avoid flicker. The paint( )<br /> method makes a quick call to checksize( ) to make sure all of the buffers have been<br /> created, then checks to see if we are dragging a letter around by means of pick != null.<br /> If so, then paint( ) makes a copy of the offscreen graphics context and clips it to the<br /> bounds of the letter it is painting, x0, y0, w0, h0. Next, it clips the onscreen graphics<br /> context to the same rectangle. This will minimize the number of pixels it will have to<br /> move for each move of the mouse.<br /> To paint, we copy the background image, offscreen, then call paint on each<br /> letter in the tray with the setting of NORMAL. Wepaint the letter we are dragging<br /> around in the BRIGHT mode. Finally, we copy the double buffer image,<br /> offscreen2, tothe screen.<br /> private Letter pick; // the letter being dragged around.<br /> private int dx, dy; // offset to topleft corner of pick.<br /> private int lw, lh; // letter width and height.<br /> private int tm, lm; // top and left margin.<br /> private int lt; // line thickness (between tiles).<br /> private int aw, ah; // letter area size.<br /> private Dimension offscreensize;<br /> private Image offscreen;<br /> private Graphics offGraphics;<br /> private Image offscreen2;<br /> private Graphics offGraphics2;<br /> public void update(Graphics g) {<br /> paint(g);<br /> }<br /> public synchronized void paint(Graphics g) {<br /> Dimension d = checksize();<br /> Graphics gc = offGraphics2;<br /> if (pick != null) {<br /> gc = gc.create();<br /> gc.clipRect(x0, y0, w0, h0);<br /> g.clipRect(x0, y0, w0, h0);<br /> }</div> <div>THE JAVA LIBRARY<br /> Chapter 19: The Applet Class 645<br /> the specified parameter in the form of a String object. Thus, for numeric and boolean<br /> values, you will need to convert their string representations into their internal formats.<br /> Here is an example that demonstrates passing parameters:<br /> // Use Parameters<br /> import java.awt.*;<br /> import java.applet.*;<br /> /*<br /> <applet code="ParamDemo" width=300 height=80><br /> <param name=fontName value=Courier><br /> <param name=fontSize value=14><br /> <param name=leading value=2><br /> <param name=accountEnabled value=true><br /> </applet><br /> */<br /> public class ParamDemo extends Applet{<br /> String fontName;<br /> int fontSize;<br /> float leading;<br /> boolean active;<br /> // Initialize the string to be displayed.<br /> public void start() {<br /> String param;<br /> fontName = getParameter("fontName");<br /> if(fontName == null)<br /> fontName = "Not Found";<br /> param = getParameter("fontSize");<br /> try {<br /> if(param != null) // if not found<br /> fontSize = Integer.parseInt(param);<br /> else<br /> fontSize = 0;<br /> } catch(NumberFormatException e) {<br /> fontSize = -1;<br /> }<br /> param = getParameter("leading");<br /> try {</div> <div>THE JAVA LANGUAGE<br /> Chapter 5: Control Statements 123<br /> To name a block, put a label at the start of it. A label is any valid Java identifier<br /> followed by a colon. Once you have labeled a block, you can then use this label as the<br /> target of a break statement. Doing so causes execution to resume at the end of the labeled<br /> block. For example, the following program shows three nested blocks, each with its<br /> own label. The break statement causes execution to jump forward, past the end of the<br /> block labeled second, skipping the two println( ) statements.<br /> // Using break as a civilized form of goto.<br /> class Break {<br /> public static void main(String args[]) {<br /> boolean t = true;<br /> }<br /> }<br /> first: {<br /> second: {<br /> third: {<br /> System.out.println("Before the break.");<br /> if(t) break second; // break out of second block<br /> System.out.println("This won't execute");<br /> }<br /> System.out.println("This won't execute");<br /> }<br /> System.out.println("This is after second block.");<br /> }<br /> Running this program generates the following output:<br /> Before the break.<br /> This is after second block.<br /> One of the most common uses for a labeled break statement is to exit from nested<br /> loops. For example, in the following program, the outer loop executes only once:<br /> // Using break to exit from nested loops<br /> class BreakLoop4 {<br /> public static void main(String args[]) {<br /> outer: for(int i=0; i<3; i++) {<br /> System.out.print("Pass " + i + ": ");<br /> for(int j=0; j<100; j++) {<br /> if(j == 10) break outer; // exit both loops<br /> System.out.print(j + " ");</div> <div>Appendix A: Using Java’s Documentation Comments 1139<br /> class will be in its own HTML file. javadoc will also output an index and a hierarchy<br /> tree. Other HTML files can be generated. Since different implementations of javadoc<br /> may work differently, you will need to check the instructions that accompany your<br /> Java development system for details specific to your version.<br /> An Example that Uses Documentation<br /> Comments<br /> Following is a sample program that uses documentation comments. Notice the way<br /> each comment immediately precedes the item that it describes. After being processed<br /> by javadoc, the documentation about the SquareNum class will be found in<br /> SquareNum.html.<br /> import java.io.*;<br /> /**<br /> * This class demonstrates documentation comments.<br /> * @author Herbert Schildt<br /> * @version 1.2<br /> */<br /> public class SquareNum {<br /> /**<br /> * This method returns the square of num.<br /> * This is a multiline description. You can use<br /> * as many lines as you like.<br /> * @param num The value to be squared.<br /> * @return num squared.<br /> */<br /> public double square(double num) {<br /> return num * num;<br /> }<br /> /**<br /> * This method inputs a number from the user.<br /> * @return The value input as a double.<br /> * @exception IOException On input error.<br /> * @see IOException<br /> */<br /> public double getNumber() throws IOException {<br /> // create a BufferedReader using System.in<br /> InputStreamReader isr = new InputStreamReader(System.in);</div> <div>THE JAVA LANGUAGE<br /> Chapter 6: Introducing Classes 147<br /> As you can see, both mybox1 and mybox2 were initialized by the Box( ) constructor<br /> when they were created. Since the constructor gives all boxes the same dimensions,<br /> 10 by 10 by 10, both mybox1 and mybox2 will have the same volume. The println( )<br /> statement inside Box( ) is for the sake of illustration only. Most constructors will not<br /> display anything. They will simply initialize an object.<br /> Before moving on, let’s reexamine the new operator. As you know, when you<br /> allocate an object, you use the following general form:<br /> class-var = new classname( );<br /> Now you can understand why the parentheses are needed after the class name. What is<br /> actually happening is that the constructor for the class is being called. Thus, in the line<br /> Box mybox1 = new Box();<br /> new Box( ) is calling the Box( ) constructor. When you do not explicitly define a constructor<br /> foraclass, then Java creates a default constructor for the class. This is why the preceding<br /> line of code worked in earlier versions of Box that did not define a constructor. The<br /> default constructor automatically initializes all instance variables to zero. The default<br /> constructor is often sufficient for simple classes, but it usually won’t do for more<br /> sophisticated ones. Once you define your own constructor, the default constructor<br /> is no longer used.<br /> Parameterized Constructors<br /> While the Box( ) constructor in the preceding example does initialize a Box object, it<br /> is not very useful—all boxes have the same dimensions. What is needed is a way to<br /> construct Box objects of various dimensions. The easy solution is to add parameters<br /> to the constructor. As you can probably guess, this makes them much more useful. For<br /> example, the following version of Box defines a parameterized constructor which sets<br /> the dimensions of a box as specified by those parameters. Pay special attention to how<br /> Box objects are created.<br /> /* Here, Box uses a parameterized constructor to<br /> initialize the dimensions of a box.<br /> */<br /> class Box {<br /> double width;<br /> double height;<br /> double depth;</div> <div>THE JAVA LANGUAGE<br /> Chapter 3: Data Types, Variables, and Arrays 55<br /> int y = 20; // known only to this block<br /> // x and y both known here.<br /> System.out.println("x and y: " + x + " " + y);<br /> x = y * 2;<br /> }<br /> // y = 100; // Error! y not known here<br /> }<br /> }<br /> // x is still known here.<br /> System.out.println("x is " + x);<br /> As the comments indicate, the variable x is declared at the start of main( )’s scope and<br /> is accessible to all subsequent code within main( ). Within the if block, y is declared.<br /> Since a block defines a scope, y is only visible to other code within its block. This is<br /> why outside of its block, the line y = 100; is commented out. If you remove the leading<br /> comment symbol, a compile-time error will occur, because y is not visible outside of its<br /> block. Within the if block, x can be used because code within a block (that is, a nested<br /> scope) has access to variables declared by an enclosing scope.<br /> Within a block, variables can be declared at any point, but are valid only after they<br /> are declared. Thus, if you define a variable at the start of a method, it is available to all<br /> of the code within that method. Conversely, if you declare a variable at the end of a<br /> block, it is effectively useless, because no code will have access to it. For example, this<br /> fragment is invalid because count cannot be used prior to its declaration:<br /> // This fragment is wrong!<br /> count = 100; // oops! cannot use count before it is declared!<br /> int count;<br /> Here is another important point to remember: variables are created when their<br /> scope is entered, and destroyed when their scope is left. This means that a variable<br /> will not hold its value once it has gone out of scope. Therefore, variables declared<br /> within a method will not hold their values between calls to that method. Also, a<br /> variable declared within a block will lose its value when the block is left. Thus, the<br /> lifetime of a variable is confined to its scope.<br /> If a variable declaration includes an initializer, then that variable will be<br /> reinitialized each time the block in which it is declared is entered. For example,<br /> consider the next program.</div> <div>THE JAVA LANGUAGE<br /> Chapter 7: A Closer Look at Methods and Classes 173<br /> An access specifier precedes the rest of a member’s type specification. That is, it<br /> must begin a member’s declaration statement. Here is an example:<br /> public int i;<br /> private double j;<br /> private int myMethod(int a, char b) { // ...<br /> To understand the effects of public and private access, consider the following<br /> program:<br /> /* This program demonstrates the difference between<br /> public and private.<br /> */<br /> class Test {<br /> int a; // default access<br /> public int b; // public access<br /> private int c; // private access<br /> }<br /> // methods to access c<br /> void setc(int i) { // set c's value<br /> c = i;<br /> }<br /> int getc() { // get c's value<br /> return c;<br /> }<br /> class AccessTest {<br /> public static void main(String args[]) {<br /> Test ob = new Test();<br /> // These are OK, a and b may be accessed directly<br /> ob.a = 10;<br /> ob.b = 20;<br /> // This is not OK and will cause an error<br /> // ob.c = 100; // Error!<br /> // You must access c through its methods<br /> ob.setc(100); // OK</div> <div>888 Java™ 2: The Complete Reference<br /> ■ When a collection of Beans has been configured and connected, it is possible to<br /> save all of this information in a persistent storage area. At a later time, this<br /> information can then be used to restore the state of the application.<br /> Sun provides two Bean application builder tools. The first is the BeanBox, which is<br /> part of the Bean Developers Kit (BDK). The BDK is the original builder tool provided<br /> by Sun. The second is the new Bean Builder. Because Bean Builder is designed to<br /> supplant the BeanBox, Sun has stopped development of the BDK and all new Bean<br /> applications will be created using Bean Builder.<br /> Although Bean Builder is the future of Bean development, it is not the sole focus of<br /> this chapter. Instead, both BeanBox and Bean Builder are discussed. The reason for this<br /> is that Bean Builder requires Java 2, version 1.4. It is incompatible with earlier versions<br /> of Java 2. This means that readers of this book using Java 2, version 1.2 or version 1.3<br /> will not be able to use Bean Builder. Instead, they must continue to use the BDK. Further,<br /> readers using version 1.4 cannot use the BDK because it is not compatible with Java 2,<br /> version 1.4. So, if you are using version 1.4, then you must use Bean Builder. If you are<br /> using a version of Java prior to 1.4, you must use the BDK. Thus, both approaches are<br /> described here, beginning with the BDK. Keep in mind that the information about Beans,<br /> Bean architecture, JAR files, and so on, apply to either Bean development tool.<br /> One other point: At the time of this writing, Java 2, version 1.4 is a released product,<br /> but Bean Builder is currently in beta testing. This means that the only way for a 1.4 user<br /> to create a Bean application is to do so using latest Bean Builder beta. For this reason,<br /> we will not examine its features in depth at this time. However, at the end of this<br /> chapter, a general overview is presented and a sample application is created.<br /> Using the Bean Developer Kit (BDK)<br /> The Bean Developer Kit (BDK), available from the JavaSoft site, is a simple example<br /> of a tool that enables you to create, configure, and connect a set of Beans. There is<br /> also a set of sample Beans with their source code. This section provides step-by-step<br /> instructions for installing and using this tool. Remember, the BDK is for use with<br /> versions of Java 2 prior to 1.4. For Java 2, v1.4 you must use the Bean Builder Tool<br /> described at the end of this chapter.<br /> In this chapter, instructions are provided for a Windows environment. The procedures<br /> for a UNIX platform are similar, but some of the commands are different.<br /> Installing the BDK<br /> The Java 2 SDK must be installed on your machine for the BDK to work. Confirm that<br /> the SDK tools are accessible from your environment.<br /> The BDK can then be downloaded from the JavaSoft site (http://java.sun.com). It is<br /> packaged as one file that is a self-extracting archive. Follow the instructions to install<br /> it on your machine. The discussion that follows assumes that the BDK is installed in</div> <div>APPLYING JAVA<br /> Chapter 32: Scrabblet: A Multiplayer Word Game 1079<br /> private Panel topPanel;<br /> private Label prompt;<br /> private TextField namefield;<br /> private Button done;<br /> private TextField chat;<br /> private List idList;<br /> private Button challenge;<br /> private Canvas ican;<br /> init( )<br /> The init( ) method is called once and simply sets up the BorderLayout, figures out<br /> what Internet host the applet came from, and creates the splash screen canvas.<br /> public void init() {<br /> setLayout(new BorderLayout());<br /> serverName = getCodeBase().getHost();<br /> if (serverName.equals(""))<br /> serverName = "localhost";<br /> ican = new IntroCanvas();<br /> }<br /> start( )<br /> The start( ) method is called whenever the browser redisplays the page in which the<br /> applet is found. The large try block at the beginning is used to catch the case where the<br /> network connection fails. If we succeed in making a new ServerConnection and we’ve<br /> never run start( ) before, we then set up the screen to prompt for the user’s name.<br /> While we are there, we put the splash screen, ican, in the center of the window. In the<br /> case where name is not null, that means the user left the page and has now returned.<br /> We presume we’ve already got the user’s name and jump right to nameEntered( ),<br /> the method that is called when the user types return in the name entry field. The<br /> validate( ) at the end makes sure all of the AWT components are updated properly.<br /> If an exception was thrown, we presume that the net connection failed and go into<br /> single-player mode. The call to start_game( ) gets things rolling.<br /> public void start() {<br /> try {<br /> showStatus("Connecting to " + serverName);<br /> server = new ServerConnection(this, serverName);</div> <div>950 Java™ 2: The Complete Reference<br /> This chapter presents an overview of servlets. Servlets are small programs that<br /> execute on the server side of a Web connection. Just as applets dynamically extend<br /> the functionality of a Web browser, servlets dynamically extend the functionality<br /> of a Web server. The topic of servlets is quite large, and it is beyond the scope of<br /> this chapter to cover it all. Instead, we will focus on the core concepts, interfaces, and<br /> classes, and develop several examples.<br /> Background<br /> In order to understand the advantages of servlets, you must have a basic understanding<br /> of how Web browsers and servers cooperate to provide content to a user. Consider<br /> a request for a static Web page. A user enters a Uniform Resource Locator (URL) into<br /> a browser. The browser generates an HTTP request to the appropriate Web server.<br /> The Web server maps this request to a specific file. That file is returned in an HTTP<br /> response to the browser. The HTTP header in the response indicates the type of the<br /> content. The Multipurpose Internet Mail Extensions (MIME) are used for this purpose.<br /> For example, ordinary ASCII text has a MIME type of text/plain. The Hypertext<br /> Markup Language (HTML) source code of a Web page has a MIME type of text/html.<br /> Now consider dynamic content. Assume that an online store uses a database to<br /> store information about its business. This would include items for sale, prices, availability,<br /> orders, and so forth. It wishes to make this information accessible to customers via<br /> Web pages. The contents of those Web pages must be dynamically generated in order<br /> to reflect the latest information in the database.<br /> In the early days of the Web, a server could dynamically construct a page by creating<br /> a separate process to handle each client request. The process would open connections<br /> to one or more databases in order to obtain the necessary information. It communicated<br /> with the Web server via an interface known as the Common Gateway Interface (CGI).<br /> CGI allowed the separate process to read data from the HTTP request and write data to<br /> the HTTP response. A variety of different languages were used to build CGI programs.<br /> These included C, C++, and Perl.<br /> However, CGI suffered serious performance problems. It was expensive in terms<br /> of processor and memory resources to create a separate process for each client request.<br /> It was also expensive to open and close database connections for each client request.<br /> In addition, the CGI programs were not platform-independent. Therefore, other<br /> techniques were introduced. Among these are servlets.<br /> Servlets offer several advantages in comparison with CGI. First, performance is<br /> significantly better. Servlets execute within the address space of a Web server. It is<br /> not necessary to create a separate process to handle each client request. Second, servlets<br /> are platform-independent because they are written in Java. A number of Web servers<br /> from different vendors offer the Servlet API. Programs developed for this API can be<br /> moved to any of these environments without recompilation. Third, the Java security<br /> manager on the server enforces a set of restrictions to protect the resources on a server</div> <div>16 Java™ 2: The Complete Reference<br /> The current release of Java is Java 2, version 1.4. This release contains several important<br /> upgrades, enhancements, and additions. For example, it adds the new keyword assert,<br /> chained exceptions, and a channel-based I/O subsystem. It also makes changes to the<br /> Collections Framework and the networking classes. In addition, numerous small changes<br /> are made throughout. Despite the significant number of new features, version 1.4<br /> maintains nearly 100 percent source-code compatibility with prior versions.<br /> This book covers all versions of Java 2. Of course, most of the material applies to<br /> earlier versions of Java, too. Throughout this book, when a feature applies to a specific<br /> version of Java, it will be so noted. Otherwise, you can simply assume that it applies to<br /> Java, in general. Also, when referring to those features common to all versions of Java 2,<br /> this book will simply use the term Java 2, without a reference to a version number.</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 25: Java Beans 893<br /> Option<br /> c<br /> C<br /> f<br /> i<br /> m<br /> M<br /> t<br /> u<br /> v<br /> x<br /> Description<br /> A new archive is to be created.<br /> Change directories during command execution.<br /> The first element in the file list is the name of the archive that is to be<br /> created or accessed.<br /> Index information should be provided.<br /> The second element in the file list is the name of the external manifest file.<br /> Manifest file not created.<br /> The archive contents should be tabulated.<br /> Update existing JAR file.<br /> Verbose output should be provided by the utility as it executes.<br /> Files are to be extracted from the archive. (If there is only one file, that<br /> is the name of the archive, and all files in it are extracted. Otherwise,<br /> the first element in the file list is the name of the archive, and the<br /> remaining elements in the list are the files that should be extracted<br /> from the archive.)<br /> 0 Do not use compression.<br /> Table 25-1.<br /> JAR Command Options<br /> Tabulating the Contents of a JAR File<br /> The following command lists the contents of Xyz.jar:<br /> jar tf Xyz.jar<br /> Extracting Files from a JAR File<br /> The following command extracts the contents of Xyz.jar and places those files in the<br /> current directory:<br /> jar xf Xyz.jar</div> <div>THE JAVA LIBRARY<br /> Chapter 15: java.util Part 1: The Collections Framework 455<br /> information by using a mechanism called hashing. In hashing, the informational content<br /> of a key is used to determine a unique value, called its hash code. The hash code is<br /> then used as the index at which the data associated with the key is stored. The<br /> transformation of the key into its hash code is performed automatically—you never see<br /> the hash code itself. Also, your code can’t directly index the hash table. The advantage<br /> of hashing is that it allows the execution time of basic operations, such as add( ),<br /> contains( ), remove( ), and size( ), to remain constant even for large sets.<br /> The following constructors are defined:<br /> HashSet( )<br /> HashSet(Collection c)<br /> HashSet(int capacity)<br /> HashSet(int capacity, float fillRatio)<br /> The first form constructs a default hash set. The second form initializes the hash<br /> set by using the elements of c. The third form initializes the capacity of the hash set to<br /> capacity. The fourth form initializes both the capacity and the fill ratio (also called load<br /> capacity) of the hash set from its arguments. The fill ratio must be between 0.0 and 1.0,<br /> and it determines how full the hash set can be before it is resized upward. Specifically,<br /> when the number of elements is greater than the capacity of the hash set multiplied by<br /> its fill ratio, the hash set is expanded. For constructors that do not take a fill ratio, 0.75<br /> is used.<br /> HashSet does not define any additional methods beyond those provided by its<br /> superclasses and interfaces.<br /> Importantly, note that a hash set does not guarantee the order of its elements,<br /> because the process of hashing doesn’t usually lend itself to the creation of sorted sets.<br /> If you need sorted storage, then another collection, such as TreeSet, is a better choice.<br /> Here is an example that demonstrates HashSet:<br /> // Demonstrate HashSet.<br /> import java.util.*;<br /> class HashSetDemo {<br /> public static void main(String args[]) {<br /> // create a hash set<br /> HashSet hs = new HashSet();<br /> // add elements to the hash set<br /> hs.add("B");<br /> hs.add("A");<br /> hs.add("D");<br /> hs.add("E");<br /> hs.add("C");<br /> hs.add("F");</div> <div>616 Java™ 2: The Complete Reference<br /> }<br /> int size = 0;<br /> int n;<br /> while ((n = in.read(file_buf)) >= 0) {<br /> uce.append(file_buf, n);<br /> size += n;<br /> }<br /> in.close();<br /> cache.put(url, uce);<br /> files_in_cache++;<br /> bytes_in_cache += uce.length;<br /> return uce;<br /> private UrlCacheEntry readFile(File f, String url)<br /> throws IOException {<br /> }<br /> if (!f.exists())<br /> return null;<br /> InputStream in = new FileInputStream(f);<br /> int file_length = in.available();<br /> String mime_type = fnameToMimeType(url);<br /> MimeHeader mh = makeMimeHeader(mime_type, file_length);<br /> UrlCacheEntry uce = loadFile(in, url, mh);<br /> return uce;<br /> private void writeDiskCache(UrlCacheEntry uce)<br /> throws IOException {<br /> }<br /> String path = docRoot + uce.url;<br /> String dir = path.substring(0, path.lastIndexOf("/"));<br /> dir.replace('/', File.separatorChar);<br /> new File(dir).mkdirs();<br /> FileOutputStream out = new FileOutputStream(path);<br /> out.write(uce.data, 0, uce.length);<br /> out.close();<br /> // A client asks us for a url that looks like this:<br /> // http://the.internet.site/the/url<br /> // we go get it from the site and return it...<br /> private void handleProxy(OutputStream out, String url,</div> <div>726 Java™ 2: The Complete Reference<br /> coordinate by this value each time you want to advance to the next line when<br /> outputting text.<br /> To start output at the end of previous output on the same line, you must know<br /> the length, in pixels, of each string that you display. To obtain this value, call<br /> stringWidth( ). You can use this value to advance the X coordinate each time you<br /> display a line.<br /> The following applet shows how to output multiple lines of text in a window. It<br /> also displays multiple sentences on the same line. Notice the variables curX and curY.<br /> They keep track of the current text output position.<br /> // Demonstrate multiline output.<br /> import java.applet.*;<br /> import java.awt.*;<br /> /*<br /> <applet code="MultiLine" width=300 height=100><br /> </applet><br /> */<br /> public class MultiLine extends Applet {<br /> int curX=0, curY=0; // current position<br /> public void init() {<br /> Font f = new Font("SansSerif", Font.PLAIN, 12);<br /> setFont(f);<br /> }<br /> public void paint(Graphics g) {<br /> FontMetrics fm = g.getFontMetrics();<br /> }<br /> nextLine("This is on line one.", g);<br /> nextLine("This is on line two.", g);<br /> sameLine(" This is on same line.", g);<br /> sameLine(" This, too.", g);<br /> nextLine("This is on line three.", g);<br /> // Advance to next line.<br /> void nextLine(String s, Graphics g) {<br /> FontMetrics fm = g.getFontMetrics();<br /> curY += fm.getHeight(); // advance to next line<br /> curX = 0;<br /> g.drawString(s, curX, curY);</div> <div>794 Java™ 2: The Complete Reference<br /> }<br /> }<br /> Extending a Check Box Group<br /> The following program reworks the preceding check box example so that the check<br /> boxes form a check box group. Thus, only one of the check boxes may be selected at<br /> any time.<br /> /*<br /> * <applet code=CheckboxGroupDemo2 width=300 height=100><br /> * </applet><br /> */<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import java.applet.*;<br /> public class CheckboxGroupDemo2 extends Applet {<br /> CheckboxGroup cbg;<br /> MyCheckbox myCheckbox1, myCheckbox2, myCheckbox3;<br /> public void init() {<br /> cbg = new CheckboxGroup();<br /> myCheckbox1 = new MyCheckbox("Item 1", cbg, true);<br /> add(myCheckbox1);<br /> myCheckbox2 = new MyCheckbox("Item 2", cbg, false);<br /> add(myCheckbox2);<br /> myCheckbox3 = new MyCheckbox("Item 3", cbg, false);<br /> add(myCheckbox3);<br /> }<br /> class MyCheckbox extends Checkbox {<br /> public MyCheckbox(String label, CheckboxGroup cbg,<br /> boolean flag) {<br /> super(label, cbg, flag);<br /> enableEvents(AWTEvent.ITEM_EVENT_MASK);<br /> }<br /> protected void processItemEvent(ItemEvent ie) {<br /> showStatus("Checkbox name/state: " + getLabel() +<br /> "/" + getState());<br /> super.processItemEvent(ie);<br /> }<br /> }<br /> }</div> <div>THE JAVA LIBRARY<br /> Chapter 21: Introducing the AWT: Working with Windows, Graphics, and Text 689<br /> Class<br /> Canvas<br /> CardLayout<br /> Checkbox<br /> CheckboxGroup<br /> CheckboxMenuItem<br /> Choice<br /> Color<br /> Component<br /> Container<br /> Cursor<br /> Dialog<br /> Dimension<br /> Event<br /> EventQueue<br /> FileDialog<br /> FlowLayout<br /> Font<br /> FontMetrics<br /> Frame<br /> Graphics<br /> GraphicsDevice<br /> Description<br /> A blank, semantics-free window.<br /> The card layout manager. Card layouts emulate<br /> index cards. Only the one on top is showing.<br /> Creates a check box control.<br /> Creates a group of check box controls.<br /> Creates an on/off menu item.<br /> Creates a pop-up list.<br /> Manages colors in a portable, platform-independent<br /> fashion.<br /> An abstract superclass for various AWT components.<br /> A subclass of Component that can hold other<br /> components.<br /> Encapsulates a bitmapped cursor.<br /> Creates a dialog window.<br /> Specifies the dimensions of an object. The width is<br /> stored in width, and the height is stored in height.<br /> Encapsulates events.<br /> Queues events.<br /> Creates a window from which a file can be selected.<br /> The flow layout manager. Flow layout positions<br /> components left to right, top to bottom.<br /> Encapsulates a type font.<br /> Encapsulates various information related to a font.<br /> This information helps you display text in a window.<br /> Creates a standard window that has a title bar, resize<br /> corners, and a menu bar.<br /> Encapsulates the graphics context. This context is<br /> used by the various output methods to display<br /> output in a window.<br /> Describes a graphics device such as a screen or printer.<br /> Table 21-1.<br /> Some AWT Classes (continued)</div> <div>xx Java™ 2: The Complete Reference<br /> Extending a Check Box Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794<br /> Extending Choice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795<br /> Extending List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795<br /> Extending Scrollbar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 797<br /> Exploring the Controls, Menus, and Layout Managers . . . . . . . . . . . . . . . . 798<br /> 23 Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 799<br /> File Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800<br /> Image Fundamentals: Creating, Loading, and Displaying . . . . . . . . . . . . . . 801<br /> Creating an Image Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 801<br /> Loading an Image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 801<br /> Displaying an Image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 802<br /> ImageObserver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 803<br /> ImageObserver Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805<br /> Double Buffering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 807<br /> MediaTracker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 811<br /> ImageProducer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815<br /> MemoryImageSource . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 815<br /> ImageConsumer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 817<br /> PixelGrabber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 818<br /> ImageFilter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 821<br /> CropImageFilter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 821<br /> RGBImageFilter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 823<br /> Cell Animation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837<br /> Additional Imaging Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 840<br /> 24 New I/O, Regular Expressions, and Other Packages . . . . . . 843<br /> The Core Java API Packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844<br /> The New I/O Packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 847<br /> NIO Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 847<br /> Charsets and Selectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 851<br /> Using the New I/O System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 851<br /> Is NIO the Future of I/O Handling? . . . . . . . . . . . . . . . . . . . . . . . . 859<br /> Regular Expression Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 859<br /> Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 859<br /> Matcher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 860<br /> Regular Expression Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861<br /> Demonstrating Pattern Matching . . . . . . . . . . . . . . . . . . . . . . . . . . . 861<br /> Two Pattern-Matching Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . 868<br /> Exploring Regular Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869<br /> Reflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 869<br /> Remote Method Invocation (RMI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874<br /> A Simple Client/Server Application Using RMI . . . . . . . . . . . . . . 874<br /> Text Formatting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 878<br /> DateFormat Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 878<br /> SimpleDateFormat Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 880</div> <div>vi Java™ 2: The Complete Reference<br /> Part II<br /> The Java Library<br /> 13 String Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347<br /> 14 Exploring java.lang . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379<br /> 15 java.util Part 1: The Collections Framework . . . . . . . . . . . . . . . 439<br /> 16 java.util Part 2: More Utility Classes . . . . . . . . . . . . . . . . . . . . . 505<br /> 17 Input/Output: Exploring java.io . . . . . . . . . . . . . . . . . . . . . . . . 537<br /> 18 Networking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 587<br /> 19 The Applet Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627<br /> 20 Event Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653<br /> 21 Introducing the AWT: Working with Windows,<br /> Graphics, and Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 687<br /> 22 Using AWT Controls, Layout Managers, and Menus . . . . . . . 735<br /> 23 Images . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 799<br /> 24 New I/O, Regular Expressions, and Other Packages . . . . . . . 843<br /> Part III<br /> Software Development Using Java<br /> 25 Java Beans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 885<br /> 26 A Tour of Swing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 921<br /> 27 Servlets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 949<br /> 28 Migrating from C++ to Java . . . . . . . . . . . . . . . . . . . . . . . . . . . . 981<br /> Part IV<br /> Applying Java<br /> 29 The DynamicBillboard Applet . . . . . . . . . . . . . . . . . . . . . . . . . . 1011<br /> 30 ImageMenu: An Image-Based Web Menu . . . . . . . . . . . . . . . . 1047<br /> 31 The Lavatron Applet: A Sports Arena Display . . . . . . . . . . . . 1057<br /> 32 Scrabblet: A Multiplayer Word Game . . . . . . . . . . . . . . . . . . . . 1069<br /> A Using Java’s Documentation Comments . . . . . . . . . . . . . . . . . . 1133<br /> Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1141</div> <div>THE JAVA LIBRARY<br /> Chapter 16: java.util Part 2: More Utility Classes 531<br /> class TwoObservers {<br /> public static void main(String args[]) {<br /> BeingWatched observed = new BeingWatched();<br /> Watcher1 observing1 = new Watcher1();<br /> Watcher2 observing2 = new Watcher2();<br /> // add both observers<br /> observed.addObserver(observing1);<br /> observed.addObserver(observing2);<br /> }<br /> }<br /> observed.counter(10);<br /> The Observable class and the Observer interface allow you to implement<br /> sophisticated program architectures based on the document/view methodology. They<br /> are also useful in multithreaded situations.<br /> Timer and TimerTask<br /> Java 2, version 1.3 added an interesting and useful feature to java.util: the ability to<br /> schedule a task for execution at some future time. The classes that support this are<br /> Timer and TimerTask. Using these classes you can create a thread that runs in the<br /> background, waiting for a specific time. When the time arrives, the task linked to<br /> that thread is executed. Various options allow you to schedule a task for repeated<br /> execution, and to schedule a task to run on a specific date. Although it was always<br /> possible to manually create a task that would be executed at a specific time using<br /> the Thread class, Timer and TimerTask greatly simplify this process.<br /> Timer and TimerTask work together. Timer is the class that you will use to<br /> schedule a task for execution. The task being scheduled must be an instance of<br /> TimerTask. Thus, to schedule a task, you will first create a TimerTask object and<br /> then schedule it for execution using an instance of Timer.<br /> TimerTask implements the Runnable interface; thus it can be used to create a<br /> thread of execution. Its constructor is shown here:<br /> TimerTask( )<br /> TimerTask defines the methods shown in Table 16-8. Notice that run( ) is abstract,<br /> which means that it must be overridden. The run( ) method, defined by the Runnable<br /> interface, contains the code that will be executed. Thus, the easiest way to create a timer<br /> task is to extend TimerTask and override run( ).</div> <div>678 Java™ 2: The Complete Reference<br /> Sample output is shown here:<br /> If you want to handle the special keys, such as the arrow or function keys, you need<br /> to respond to them within the keyPressed( ) handler. They are not available through<br /> keyTyped( ).Toidentify the keys, you use their virtual key codes. For example, the next<br /> applet outputs the name of a few of the special keys:<br /> // Demonstrate some virtual key codes.<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import java.applet.*;<br /> /*<br /> <applet code="KeyEvents" width=300 height=100><br /> </applet><br /> */<br /> public class KeyEvents extends Applet<br /> implements KeyListener {<br /> String msg = "";<br /> int X = 10, Y = 20; // output coordinates<br /> public void init() {<br /> addKeyListener(this);<br /> requestFocus(); // request input focus<br /> }<br /> public void keyPressed(KeyEvent ke) {<br /> showStatus("Key Down");<br /> int key = ke.getKeyCode();<br /> switch(key) {</div> <div>THE JAVA LIBRARY<br /> Chapter 24: New I/O, Regular Expressions, and Other Packages 845<br /> Package<br /> java.awt.event<br /> java.awt.font<br /> java.awt.geom<br /> java.awt.im<br /> java.awt.im.spi<br /> java.awt.image<br /> java.awt.image.renderable<br /> java.awt.print<br /> java.beans<br /> java.beans.beancontext<br /> java.io<br /> java.lang<br /> java.lang.ref<br /> java.lang.reflect<br /> java.math<br /> java.net<br /> java.nio<br /> java.nio.channels<br /> java.nio.channels.spi<br /> Primary Function<br /> Handles events.<br /> Represents various types of fonts.<br /> Allows you to work with<br /> geometric shapes.<br /> Allows input of Japanese, Chinese, and<br /> Korean characters to text editing components.<br /> Supports alternative input devices. (Added by<br /> Java 2, v1.3)<br /> Processes images.<br /> Supports rendering-independent images.<br /> Supports general print capabilities.<br /> Allows you to build software components.<br /> Provides an execution environment<br /> for beans.<br /> Inputs and outputs data.<br /> Provides core functionality.<br /> Enables some interaction with the<br /> garbage collector.<br /> Analyzes code at run time.<br /> Handles large integers and<br /> decimal numbers.<br /> Supports networking.<br /> Top-level package for the new Java I/O<br /> classes. Encapsulates buffers. (Added by Java<br /> 2, v1.4)<br /> Encapsulates channels, which are used by the<br /> new I/O system. (Added by Java 2, v1.4)<br /> Supports service providers for channels.<br /> (Added by Java 2, v1.4)<br /> Table 24-1.<br /> The Core Java API Packages (continued)</div> <div>THE JAVA LIBRARY<br /> Chapter 18: Networking 599<br /> openConnection( ) has the following general form:<br /> URLConnection openConnection( )<br /> It returns a URLConnection object associated with the invoking URL object. It may<br /> throw an IOException.<br /> URLConnection<br /> URLConnection is a general-purpose class for accessing the attributes of a remote<br /> resource. Once you make a connection to a remote server, you can use URLConnection<br /> to inspect the properties of the remote object before actually transporting it locally.<br /> These attributes are exposed by the HTTP protocol specification and, as such, only<br /> make sense for URL objects that are using the HTTP protocol. We’ll examine the most<br /> useful elements of URLConnection here.<br /> In the following example, we create a URLConnection using the openConnection( )<br /> method of a URL object and then use it to examine the document’s properties and content:<br /> // Demonstrate URLConnection.<br /> import java.net.*;<br /> import java.io.*;<br /> import java.util.Date;<br /> class UCDemo<br /> {<br /> public static void main(String args[]) throws Exception {<br /> int c;<br /> URL hp = new URL("http://www.internic.net");<br /> URLConnection hpCon = hp.openConnection();<br /> // get date<br /> long d = hpCon.getDate();<br /> if(d==0)<br /> System.out.println("No date information.");<br /> else<br /> System.out.println("Date: " + new Date(d));<br /> // get content type<br /> System.out.println("Content-Type: " + hpCon.getContentType());<br /> // get expiration date<br /> d = hpCon.getExpiration();<br /> if(d==0)</div> <div>This page intentionally left blank.</div> <div>THE JAVA LIBRARY<br /> Chapter 19: The Applet Class 643<br /> The HTML APPLET Tag<br /> The APPLET tag is used to start an applet from both an HTML document and from an<br /> applet viewer. (The newer OBJECT tag also works, but this book will use APPLET.)<br /> An applet viewer will execute each APPLET tag that it finds in a separate window,<br /> while web browsers like Netscape Navigator, Internet Explorer, and HotJava will allow<br /> many applets on a single page. So far, we have been using only a simplified form of the<br /> APPLET tag. Now it is time to take a closer look at it.<br /> The syntax for the standard APPLET tag is shown here. Bracketed items<br /> are optional.<br /> < APPLET<br /> [CODEBASE = codebaseURL]<br /> CODE = appletFile<br /> [ALT = alternateText]<br /> [NAME = appletInstanceName]<br /> WIDTH = pixels HEIGHT = pixels<br /> [ALIGN = alignment]<br /> [VSPACE = pixels] [HSPACE = pixels]<br /> ><br /> [< PARAM NAME = AttributeName VALUE = AttributeValue>]<br /> [< PARAM NAME = AttributeName2 VALUE = AttributeValue>]<br /> . . .<br /> [HTML Displayed in the absence of Java]<br /> </APPLET><br /> Let’s take a look at each part now.<br /> CODEBASE CODEBASE is an optional attribute that specifies the base URL of the<br /> applet code, which is the directory that will be searched for the applet’s executable<br /> class file (specified by the CODE tag). The HTML document’s URL directory is used as<br /> the CODEBASE if this attribute is not specified. The CODEBASE does not have to be<br /> on the host from which the HTML document was read.<br /> CODE CODE is a required attribute that gives the name of the file containing your<br /> applet’s compiled .class file. This file is relative to the code base URL of the applet,<br /> which is the directory that the HTML file was in or the directory indicated by<br /> CODEBASE if set.<br /> ALT The ALT tag is an optional attribute used to specify a short text message that<br /> should be displayed if the browser understands the APPLET tag but can’t currently<br /> run Java applets. This is distinct from the alternate HTML you provide for browsers<br /> that don’t support applets.</div> <div>APPLYING JAVA<br /> Chapter 32: Scrabblet: A Multiplayer Word Game 1091<br /> g.drawString(s, (w - fm.stringWidth(s)) / 2 + off, y + off);<br /> }<br /> public void paint(Graphics g) {<br /> Dimension d = getSize();<br /> w = d.width;<br /> h = d.height;<br /> g.setColor(blue);<br /> g.fill3DRect(edge, edge, w - 2 * edge, h - 2 * edge, true);<br /> d(g, title, Color.black, titlefont, h / 2, 1);<br /> d(g, title, Color.white, titlefont, h / 2, -1);<br /> d(g, title, pink, titlefont, h / 2, 0);<br /> d(g, name, Color.black, namefont, h * 3 / 4, 0);<br /> d(g, book, Color.black, bookfont, h * 7 / 8, 0);<br /> }<br /> mousePressed( )<br /> In the following code fragment, notice that MyMouseAdapter is an inner class that<br /> extends MouseAdapter. It overrides the mousePressed( ) method to cause this canvas’<br /> parent to hide( ) if it is clicked on. This is only useful in single-player mode to dismiss<br /> the pop-up frame.<br /> }<br /> class MyMouseAdapter extends MouseAdapter {<br /> public void mousePressed(MouseEvent me) {<br /> ((Frame)getParent()).setVisible(false);<br /> }<br /> }<br /> Board.java<br /> The Board class encapsulates most of the game logic as well as the look and feel of the<br /> board. It is the biggest class in the game, weighing in at over 500 lines of code. There<br /> are several private variables that store the game state. The 15×15 array of Letters<br /> named board is used to store the tiles on each square of the board. The tray array holds<br /> the Letters that are currently on our tray. Remember that the Scrabblet applet class<br /> holds the seven Letters from our opponent. The Point objects orig and here are used to<br /> remember letter positions. The name and others_name variables are used simply to<br /> display names for the scoreboard. In single-player mode, both will be null. The two<br /> players’ scores are stored in total_score and others_score, while our last turn’s result is</div> <div>672 Java™ 2: The Complete Reference<br /> The MouseWheelListener Interface<br /> This interface defines the mouseWheelMoved( ) method that is invoked when the<br /> mouse wheel is moved. Its general form is shown here.<br /> void mouseWheelMoved(MouseWheelEvent mwe)<br /> MouseWheelListener was added by Java 2, version 1.4.<br /> The TextListener Interface<br /> This interface defines the textChanged( ) method that is invoked when a change occurs<br /> in a text area or text field. Its general form is shown here:<br /> void textChanged(TextEvent te)<br /> The WindowFocusListener Interface<br /> This interface defines two methods: windowGainedFocus( ) and windowLostFocus( ).<br /> These are called when a window gains or losses input focus. Their general forms are<br /> shown here.<br /> void windowGainedFocus(WindowEvent we)<br /> void windowLostFocus(WindowEvent we)<br /> WindowFocusListener was added by Java 2, version 1.4.<br /> The WindowListener Interface<br /> This interface defines seven methods. The windowActivated( ) and windowDeactivated( )<br /> methods are invoked when a window is activated or deactivated, respectively. If a<br /> window is iconified, the windowIconified( ) method is called. When a window is deiconified,<br /> the windowDeiconified( ) method is called. When a window is opened or closed,<br /> the windowOpened( ) or windowClosed( ) methods are called, respectively. The<br /> windowClosing( ) method is called when a window is being closed. The general forms<br /> of these methods are<br /> void windowActivated(WindowEvent we)<br /> void windowClosed(WindowEvent we)<br /> void windowClosing(WindowEvent we)<br /> void windowDeactivated(WindowEvent we)<br /> void windowDeiconified(WindowEvent we)<br /> void windowIconified(WindowEvent we)<br /> void windowOpened(WindowEvent we)</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 25: Java Beans 887<br /> Advantages of Java Beans<br /> A software component architecture provides standard mechanisms to deal with<br /> software building blocks. The following list enumerates some of the specific benefits<br /> that Java technology provides for a component developer:<br /> ■ A Bean obtains all the benefits of Java’s “write-once, run-anywhere” paradigm.<br /> ■ The properties, events, and methods of a Bean that are exposed to an<br /> application builder tool can be controlled.<br /> ■ A Bean may be designed to operate correctly in different locales, which makes it<br /> useful in global markets.<br /> ■ Auxiliary software can be provided to help a person configure a Bean. This<br /> software is only needed when the design-time parameters for that component<br /> are being set. It does not need to be included in the run-time environment.<br /> ■ The configuration settings of a Bean can be saved in persistent storage and<br /> restored at a later time.<br /> ■ A Bean may register to receive events from other objects and can generate<br /> events that are sent to other objects.<br /> Application Builder Tools<br /> When working with Java Beans, most developers use an application builder tool, a utility<br /> that enables you to configure a set of Beans, connect them together, and produce a<br /> working application. In general, Bean builder tools have the following capabilities.<br /> ■ A palette is provided that lists all of the available Beans. As additional Beans<br /> are developed or purchased, they can be added to the palette.<br /> ■ A worksheet is displayed that allows the designer to lay out Beans in a graphical<br /> user interface. A designer may drag and drop a Bean from the palette to this<br /> worksheet.<br /> ■ Special editors and customizers allow a Bean to be configured. This is the<br /> mechanism by which the behavior of a Bean may be adapted for a particular<br /> environment.<br /> ■ Commands allow a designer to inquire about the state and behavior of a<br /> Bean. This information automatically becomes available when a Bean is added<br /> to the palette.<br /> ■ Capabilities exist to interconnect Beans. This means that events generated by<br /> one component are mapped to method invocations on other components.</div> <div>THE JAVA LIBRARY<br /> Chapter 18: Networking 621<br /> their corresponding methods in the httpd. Any time a message is logged, the<br /> bottom-right Label object is updated to contain the latest statistics from the httpd.<br /> import java.util.*;<br /> import java.applet.*;<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> public class HTTP extends Applet implements LogMessage,<br /> ActionListener<br /> {<br /> private int m_port = 80;<br /> private String m_docroot = "c:\\www";<br /> private httpd m_httpd;<br /> private TextArea m_log;<br /> private Label status;<br /> private final String PARAM_port = "port";<br /> private final String PARAM_docroot = "docroot";<br /> public HTTP() {<br /> }<br /> public void init() {<br /> setBackground(Color.white);<br /> String param;<br /> // port: Port number to listen on<br /> param = getParameter(PARAM_port);<br /> if (param != null)<br /> m_port = Integer.parseInt(param);<br /> // docroot: web document root<br /> param = getParameter(PARAM_docroot);<br /> if (param != null)<br /> m_docroot = param;<br /> setLayout(new BorderLayout());<br /> Label lab = new Label("Java HTTPD");<br /> lab.setFont(new Font("SansSerif", Font.BOLD, 18));</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 26: A Tour of Swing 931<br /> // Get content pane<br /> Container contentPane = getContentPane();<br /> contentPane.setLayout(new FlowLayout());<br /> // Create icons<br /> ImageIcon normal = new ImageIcon("normal.gif");<br /> ImageIcon rollover = new ImageIcon("rollover.gif");<br /> ImageIcon selected = new ImageIcon("selected.gif");<br /> // Add check boxes to the content pane<br /> JCheckBox cb = new JCheckBox("C", normal);<br /> cb.setRolloverIcon(rollover);<br /> cb.setSelectedIcon(selected);<br /> cb.addItemListener(this);<br /> contentPane.add(cb);<br /> cb = new JCheckBox("C++", normal);<br /> cb.setRolloverIcon(rollover);<br /> cb.setSelectedIcon(selected);<br /> cb.addItemListener(this);<br /> contentPane.add(cb);<br /> }<br /> }<br /> cb = new JCheckBox("Java", normal);<br /> cb.setRolloverIcon(rollover);<br /> cb.setSelectedIcon(selected);<br /> cb.addItemListener(this);<br /> contentPane.add(cb);<br /> cb = new JCheckBox("Perl", normal);<br /> cb.setRolloverIcon(rollover);<br /> cb.setSelectedIcon(selected);<br /> cb.addItemListener(this);<br /> contentPane.add(cb);<br /> // Add text field to the content pane<br /> jtf = new JTextField(15);<br /> contentPane.add(jtf);<br /> public void itemStateChanged(ItemEvent ie) {<br /> JCheckBox cb = (JCheckBox)ie.getItem();<br /> jtf.setText(cb.getText());<br /> }</div> <div>852 Java™ 2: The Complete Reference<br /> file channels operate on byte buffers you will use the allocate( ) method defined by<br /> ByteBuffer. It has this general form.<br /> static ByteBuffer allocate(int cap)<br /> Here, cap specifies the capacity of the buffer. A reference to the buffer is returned. After<br /> you have created the buffer, call read( ) on the channel, passing a reference to the buffer.<br /> The following program shows how to read a text file called test.txt through a<br /> channel using explicit input operations.<br /> // Use the new I/O system to read a text file.<br /> import java.io.*;<br /> import java.nio.*;<br /> import java.nio.channels.*;<br /> public class ExplicitChannelRead {<br /> public static void main(String args[])<br /> FileInputStream fIn;<br /> FileChannel fChan;<br /> long fSize;<br /> ByteBuffer mBuf;<br /> try<br /> // First, open a file for input.<br /> fIn = new FileInputStream("test.txt");<br /> // Next, obtain a channel to that file.<br /> fChan = fIn.getChannel();<br /> // Now, get the file's size.<br /> fSize = fChan.size();<br /> // Allocate a buffer of the necessary size.<br /> mBuf = ByteBuffer.allocate((int)fSize);<br /> // Read the file into the buffer.<br /> fChan.read(mBuf);<br /> // Rewind the buffer so that it can be read.<br /> mBuf.rewind();<br /> // Read bytes from the buffer.<br /> for(int i=0; i < fSize; i++)</div> <div>12 Java™ 2: The Complete Reference<br /> Although Java was designed for interpretation, there is technically nothing about<br /> Java that prevents on-the-fly compilation of bytecode into native code. Along these<br /> lines, Sun supplies its Just In Time (JIT) compiler for bytecode, which is included in<br /> the Java 2 release. When the JIT compiler is part of the JVM, it compiles bytecode into<br /> executable code in real time, on a piece-by-piece, demand basis. It is important to<br /> understand that it is not possible to compile an entire Java program into executable<br /> code all at once, because Java performs various run-time checks that can be done only<br /> at run time. Instead, the JIT compiles code as it is needed, during execution. However,<br /> the just-in-time approach still yields a significant performance boost. Even when<br /> dynamic compilation is applied to bytecode, the portability and safety features still<br /> apply, because the run-time system (which performs the compilation) still is in charge<br /> of the execution environment. Whether your Java program is actually interpreted in the<br /> traditional way or compiled on-the-fly, its functionality is the same.<br /> The Java Buzzwords<br /> No discussion of the genesis of Java is complete without a look at the Java buzzwords.<br /> Although the fundamental forces that necessitated the invention of Java are portability<br /> and security, other factors also played an important role in molding the final form of<br /> the language. The key considerations were summed up by the Java team in the<br /> following list of buzzwords:<br /> ■ Simple<br /> ■ Secure<br /> ■ Portable<br /> ■ Object-oriented<br /> ■ Robust<br /> ■ Multithreaded<br /> ■ Architecture-neutral<br /> ■ Interpreted<br /> ■ High performance<br /> ■ Distributed<br /> ■ Dynamic<br /> Two of these buzzwords have already been discussed: secure and portable. Let’s<br /> examine what each of the others implies.</div> <div>648 Java™ 2: The Complete Reference<br /> }<br /> }<br /> char ch;<br /> // Display banner<br /> for( ; ; ) {<br /> try {<br /> repaint();<br /> Thread.sleep(250);<br /> ch = msg.charAt(0);<br /> msg = msg.substring(1, msg.length());<br /> msg += ch;<br /> if(stopFlag)<br /> break;<br /> } catch(InterruptedException e) {}<br /> }<br /> // Pause the banner.<br /> public void stop() {<br /> stopFlag = true;<br /> t = null;<br /> }<br /> // Display the banner.<br /> public void paint(Graphics g) {<br /> g.drawString(msg, 50, 30);<br /> }<br /> getDocumentBase( ) and getCodeBase( )<br /> Often, you will create applets that will need to explicitly load media and text. Java will<br /> allow the applet to load data from the directory holding the HTML file that started the<br /> applet (the document base) and the directory from which the applet’s class file was<br /> loaded (the code base). These directories are returned as URL objects (described in<br /> Chapter 18) by getDocumentBase( ) and getCodeBase( ). They can be concatenated<br /> with a string that names the file you want to load. To actually load another file, you<br /> will use the showDocument( ) method defined by the AppletContext interface,<br /> discussed in the next section.<br /> The following applet illustrates these methods:<br /> // Display code and document bases.</div> <div>324 Java™ 2: The Complete Reference<br /> The following application illustrates using a PrintWriter to handle console output:<br /> // Demonstrate PrintWriter<br /> import java.io.*;<br /> public class PrintWriterDemo {<br /> public static void main(String args[]) {<br /> PrintWriter pw = new PrintWriter(System.out, true);<br /> pw.println("This is a string");<br /> int i = -7;<br /> pw.println(i);<br /> double d = 4.5e-7;<br /> pw.println(d);<br /> }<br /> }<br /> The output from this program is shown here:<br /> This is a string<br /> -7<br /> 4.5E-7<br /> Remember, there is nothing wrong with using System.out to write simple text<br /> output to the console when you are learning Java or debugging your programs.<br /> However, using a PrintWriter will make your real-world applications easier to<br /> internationalize. Because no advantage is gained by using a PrintWriter in the<br /> sample programs shown in this book, we will continue to use System.out to write<br /> to the console.<br /> Reading and Writing Files<br /> Java provides a number of classes and methods that allow you to read and write files.<br /> In Java, all files are byte-oriented, and Java provides methods to read and write bytes<br /> from and to a file. However, Java allows you to wrap a byte-oriented file stream within<br /> a character-based object. This technique is described in Part II. This chapter examines<br /> the basics of file I/O.<br /> Two of the most often-used stream classes are FileInputStream and<br /> FileOutputStream, which create byte streams linked to files. To open a file, you simply<br /> create an object of one of these classes, specifying the name of the file as an argument to<br /> the constructor. While both classes support additional, overridden constructors, the<br /> following are the forms that we will be using:</div> <div>682 Java™ 2: The Complete Reference<br /> }<br /> this.adapterDemo = adapterDemo;<br /> }<br /> // Handle mouse clicked.<br /> public void mouseClicked(MouseEvent me) {<br /> adapterDemo.showStatus("Mouse clicked");<br /> }<br /> class MyMouseMotionAdapter extends MouseMotionAdapter {<br /> AdapterDemo adapterDemo;<br /> public MyMouseMotionAdapter(AdapterDemo adapterDemo) {<br /> this.adapterDemo = adapterDemo;<br /> }<br /> }<br /> // Handle mouse dragged.<br /> public void mouseDragged(MouseEvent me) {<br /> adapterDemo.showStatus("Mouse dragged");<br /> }<br /> As you can see by looking at the program, not having to implement all of the<br /> methods defined by the MouseMotionListener and MouseListener interfaces saves<br /> you a considerable amount of effort and prevents your code from becoming cluttered<br /> with empty methods. As an exercise, you might want to try rewriting one of the<br /> keyboard input examples shown earlier so that it uses a KeyAdapter.<br /> Inner Classes<br /> In Chapter 7, the basics of inner classes were explained. Here you will see why they are<br /> important. Recall that an inner class is a class defined within other class, or even within<br /> an expression. This section illustrates how inner classes can be used to simplify the<br /> code when using event adapter classes.<br /> To understand the benefit provided by inner classes, consider the applet shown<br /> in the following listing. It does not use an inner class. Its goal is to display the string<br /> “Mouse Pressed” in the status bar of the applet viewer or browser when the mouse<br /> is pressed. There are two top-level classes in this program. MousePressedDemo<br /> extends Applet, and MyMouseAdapter extends MouseAdapter. The init( ) method<br /> of MousePressedDemo instantiates MyMouseAdapter and provides this object as<br /> an argument to the addMouseListener( ) method.<br /> Notice that a reference to the applet is supplied as an argument to the MyMouseAdapter<br /> constructor. This reference is stored in an instance variable for later use by the mousePressed( )<br /> method. When the mouse is pressed, it invokes the showStatus( ) method of the applet</div> <div>618 Java™ 2: The Complete Reference<br /> }<br /> out.write(uce.data, 0, uce.length);<br /> writeDiskCache(uce);<br /> logEntry("GET", site + server_url, 200, uce.length);<br /> }<br /> server_out.close();<br /> server.close();<br /> }<br /> } catch (IOException e) {<br /> log.log("Exception: " + e);<br /> }<br /> private void handleGet(OutputStream out, String url,<br /> MimeHeader inmh) {<br /> byte file_buf[] = new byte[buffer_size];<br /> String filename = docRoot + url +<br /> (url.endsWith("/") ? indexfile : "");<br /> try {<br /> if (!serveFromCache(out, url)) {<br /> File f = new File(filename);<br /> if (! f.exists()) {<br /> writeString(out, error(404, "Not Found", filename));<br /> return;<br /> }<br /> if (! f.canRead()) {<br /> writeString(out, error(404, "Permission Denied", filename));<br /> return;<br /> }<br /> UrlCacheEntry uce = readFile(f, url);<br /> writeUCE(out, uce);<br /> }<br /> } catch (IOException e) {<br /> log.log("Exception: " + e);<br /> }<br /> }<br /> private void doRequest(Socket s) throws IOException {<br /> if(stopFlag)<br /> return;<br /> InputStream in = s.getInputStream();<br /> OutputStream out = s.getOutputStream();<br /> String request = getRawRequest(in);</div> <div>674 Java™ 2: The Complete Reference<br /> public class MouseEvents extends Applet<br /> implements MouseListener, MouseMotionListener {<br /> String msg = "";<br /> int mouseX = 0, mouseY = 0; // coordinates of mouse<br /> public void init() {<br /> addMouseListener(this);<br /> addMouseMotionListener(this);<br /> }<br /> // Handle mouse clicked.<br /> public void mouseClicked(MouseEvent me) {<br /> // save coordinates<br /> mouseX = 0;<br /> mouseY = 10;<br /> msg = "Mouse clicked.";<br /> repaint();<br /> }<br /> // Handle mouse entered.<br /> public void mouseEntered(MouseEvent me) {<br /> // save coordinates<br /> mouseX = 0;<br /> mouseY = 10;<br /> msg = "Mouse entered.";<br /> repaint();<br /> }<br /> // Handle mouse exited.<br /> public void mouseExited(MouseEvent me) {<br /> // save coordinates<br /> mouseX = 0;<br /> mouseY = 10;<br /> msg = "Mouse exited.";<br /> repaint();<br /> }<br /> // Handle button pressed.</div> <div>188 Java™ 2: The Complete Reference<br /> Using Command-Line Arguments<br /> Sometimes you will want to pass information into a program when you run it. This<br /> is accomplished by passing command-line arguments to main( ). A command-line<br /> argument is the information that directly follows the program’s name on the command<br /> line when it is executed. To access the command-line arguments inside a Java program<br /> is quite easy—they are stored as strings in the String array passed to main( ). For<br /> example, the following program displays all of the command-line arguments that it<br /> is called with:<br /> // Display all command-line arguments.<br /> class CommandLine {<br /> public static void main(String args[]) {<br /> for(int i=0; i<args.length; i++)<br /> System.out.println("args[" + i + "]: " +<br /> args[i]);<br /> }<br /> }<br /> Try executing this program, as shown here:<br /> java CommandLine this is a test 100 -1<br /> When you do, you will see the following output:<br /> args[0]: this<br /> args[1]: is<br /> args[2]: a<br /> args[3]: test<br /> args[4]: 100<br /> args[5]: -1<br /> All command-line arguments are passed as strings. You must convert numeric values to<br /> their internal forms manually, as explained in Chapter 14.</div> <div>THE JAVA LIBRARY<br /> Chapter 17: Input/Output: Exploring java.io 573<br /> operates on the standard input stream. If one or more filenames are specified, the<br /> program operates on each of them.<br /> // A word counting utility.<br /> import java.io.*;<br /> class WordCount {<br /> public static int words = 0;<br /> public static int lines = 0;<br /> public static int chars = 0;<br /> public static void wc(InputStreamReader isr)<br /> throws IOException {<br /> int c = 0;<br /> boolean lastWhite = true;<br /> String whiteSpace = " \t\n\r";<br /> }<br /> while ((c = isr.read()) != -1) {<br /> // Count characters<br /> chars++;<br /> // Count lines<br /> if (c == '\n') {<br /> lines++;<br /> }<br /> // Count words by detecting the start of a word<br /> int index = whiteSpace.indexOf(c);<br /> if(index == -1) {<br /> if(lastWhite == true) {<br /> ++words;<br /> }<br /> lastWhite = false;<br /> }<br /> else {<br /> lastWhite = true;<br /> }<br /> }<br /> if(chars != 0) {<br /> ++lines;<br /> }<br /> public static void main(String args[]) {</div> <div>1080 Java™ 2: The Complete Reference<br /> }<br /> server.start();<br /> showStatus("Connected: " + serverName);<br /> if (name == null) {<br /> prompt = new Label("Enter your name here:");<br /> namefield = new TextField(20);<br /> namefield.addActionListener(this);<br /> topPanel = new Panel();<br /> topPanel.setBackground(new Color(255, 255, 200));<br /> topPanel.add(prompt);<br /> topPanel.add(namefield);<br /> add("North", topPanel);<br /> add("Center", ican);<br /> } else {<br /> if (chat != null) {<br /> remove(chat);<br /> remove(board);<br /> remove(done);<br /> }<br /> nameEntered(name);<br /> }<br /> validate();<br /> } catch (Exception e) {<br /> single = true;<br /> start_Game((int)(0x7fffffff * Math.random()));<br /> }<br /> stop( )<br /> The stop( ) method is called whenever the user leaves the page with the applet. Here,<br /> we just tell the server that we’ve left. We re-create the network connection in start( ) if<br /> the user returns to the page later.<br /> public void stop() {<br /> if (!single)<br /> server.quit();<br /> }</div> <div>THE JAVA LIBRARY<br /> Chapter 14: Exploring java.lang 415<br /> Here, the method cloneTest( ) calls clone( ) in Object and returns the result. Notice<br /> that the object returned by clone( ) must be cast into its appropriate type (TestClone).<br /> The following example overrides clone( ) so that it can be called from code outside<br /> of its class. To do this, its access specifier must be public, as shown here:<br /> // Override the clone() method.<br /> class TestClone implements Cloneable {<br /> int a;<br /> double b;<br /> }<br /> // clone() is now overridden and is public.<br /> public Object clone() {<br /> try {<br /> // call clone in Object.<br /> return super.clone();<br /> } catch(CloneNotSupportedException e) {<br /> System.out.println("Cloning not allowed.");<br /> return this;<br /> }<br /> }<br /> class CloneDemo2 {<br /> public static void main(String args[]) {<br /> TestClone x1 = new TestClone();<br /> TestClone x2;<br /> x1.a = 10;<br /> x1.b = 20.98;<br /> // here, clone() is called directly.<br /> x2 = (TestClone) x1.clone();<br /> }<br /> }<br /> System.out.println("x1: " + x1.a + " " + x1.b);<br /> System.out.println("x2: " + x2.a + " " + x2.b);<br /> The side effects caused by cloning are sometimes difficult to see at first. It is easy to<br /> think that a class is safe for cloning when it actually is not. In general, you should not<br /> implement Cloneable for any class without good reason.</div> <div>THE JAVA LIBRARY<br /> Chapter 14: Exploring java.lang 423<br /> Compiler<br /> The Compiler class supports the creation of Java environments in which Java bytecode<br /> is compiled into executable code rather than interpreted. It is not for normal<br /> programming use.<br /> Thread, ThreadGroup, and Runnable<br /> The Runnable interface and the Thread and ThreadGroup classes support<br /> multithreaded programming. Each is examined next.<br /> An overview of the techniques used to manage threads, implement the Runnable<br /> interface, and create multithreaded programs is presented in Chapter 11.<br /> The Runnable Interface<br /> The Runnable interface must be implemented by any class that will initiate a separate<br /> thread of execution. Runnable only defines one abstract method, called run( ), which is<br /> the entry point to the thread. It is defined like this:<br /> abstract void run( )<br /> Threads that you create must implement this method.<br /> Thread<br /> Thread creates a new thread of execution. It defines the following commonly<br /> used constructors:<br /> Thread( )<br /> Thread(Runnable threadOb)<br /> Thread(Runnable threadOb, StringthreadName)<br /> Thread(String threadName)<br /> Thread(ThreadGroup groupOb, Runnable threadOb)<br /> Thread(ThreadGroup groupOb, Runnable threadOb, String threadName)<br /> Thread(ThreadGroup groupOb, String threadName)<br /> threadOb is an instance of a class that implements the Runnable interface and defines<br /> where execution of the thread will begin. The name of the thread is specified by<br /> threadName. When a name is not specified, one is created by the Java Virtual Machine.<br /> groupOb specifies the thread group to which the new thread will belong. When no thread<br /> group is specified, the new thread belongs to the same group as the parent thread.<br /> The following constants are defined by Thread:<br /> MAX_PRIORITY<br /> MIN_PRIORITY<br /> NORM_PRIORITY</div> <div>xii Java™ 2: The Complete Reference<br /> Messaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276<br /> The Thread Class and the Runnable Interface . . . . . . . . . . . . . . . . 277<br /> The Main Thread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277<br /> Creating a Thread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280<br /> Implementing Runnable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280<br /> Extending Thread . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282<br /> Choosing an Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284<br /> Creating Multiple Threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284<br /> Using isAlive( ) and join( ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286<br /> Thread Priorities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289<br /> Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292<br /> Using Synchronized Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292<br /> The synchronized Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295<br /> Interthread Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297<br /> Deadlock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302<br /> Suspending, Resuming, and Stopping Threads . . . . . . . . . . . . . . . . . . . . . . . 305<br /> Suspending, Resuming, and Stopping Threads Using<br /> Java 1.1 and Earlier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305<br /> Suspending, Resuming, and Stopping Threads Using<br /> Java 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308<br /> Using Multithreading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311<br /> 12 I/O, Applets, and Other Topics . . . . . . . . . . . . . . . . . . . . . . . . 313<br /> I/O Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314<br /> Streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314<br /> Byte Streams and Character Streams . . . . . . . . . . . . . . . . . . . . . . . . 315<br /> The Predefined Streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318<br /> Reading Console Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318<br /> Reading Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319<br /> Reading Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320<br /> Writing Console Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322<br /> The PrintWriter Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323<br /> Reading and Writing Files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324<br /> Applet Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328<br /> The transient and volatile Modifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331<br /> Using instanceof . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332<br /> strictfp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335<br /> Native Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 335<br /> Problems with Native Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340<br /> Using assert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340<br /> Assertion Enabling and Disabling Options . . . . . . . . . . . . . . . . . . . 343<br /> Part II<br /> The Java Library<br /> 13 String Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347<br /> The String Constructors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348<br /> String Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351</div> <div>102 Java™ 2: The Complete Reference<br /> It seems clear that the statement bytesAvailable = n; was intended to be executed<br /> inside the else clause, because of the indentation level. However, as you recall,<br /> whitespace is insignificant to Java, and there is no way for the compiler to know what<br /> was intended. This code will compile without complaint, but it will behave incorrectly<br /> when run. The preceding example is fixed in the code that follows:<br /> int bytesAvailable;<br /> // ...<br /> if (bytesAvailable > 0) {<br /> ProcessData();<br /> bytesAvailable -= n;<br /> } else {<br /> waitForMoreData();<br /> bytesAvailable = n;<br /> }<br /> Nested ifs<br /> A nested if is an if statement that is the target of another if or else. Nested ifs are very<br /> common in programming. When you nest ifs, the main thing to remember is that an<br /> else statement always refers to the nearest if statement that is within the same block<br /> as the else and that is not already associated with an else. Here is an example:<br /> if(i == 10) {<br /> if(j < 20) a = b;<br /> if(k > 100) c = d; // this if is<br /> else a = c; // associated with this else<br /> }<br /> else a = d; // this else refers to if(i == 10)<br /> As the comments indicate, the final else is not associated with if(j<20), because it is not<br /> in the same block (even though it is the nearest if without an else). Rather, the final else<br /> is associated with if(i==10). The inner else refers to if(k>100), because it is the closest if<br /> within the same block.<br /> The if-else-if Ladder<br /> A common programming construct that is based upon a sequence of nested ifs is the<br /> if-else-if ladder. It looks like this:<br /> if(condition)<br /> statement;<br /> else if(condition)</div> <div>684 Java™ 2: The Complete Reference<br /> public class InnerClassDemo extends Applet {<br /> public void init() {<br /> addMouseListener(new MyMouseAdapter());<br /> }<br /> class MyMouseAdapter extends MouseAdapter {<br /> public void mousePressed(MouseEvent me) {<br /> showStatus("Mouse Pressed");<br /> }<br /> }<br /> }<br /> Anonymous Inner Classes<br /> An anonymous inner class is one that is not assigned a name. This section illustrates how<br /> an anonymous inner class can facilitate the writing of event handlers. Consider the applet<br /> shown in the following listing. As before, its goal is to display the string “Mouse Pressed”<br /> in the status bar of the applet viewer or browser when the mouse is pressed.<br /> // Anonymous inner class demo.<br /> import java.applet.*;<br /> import java.awt.event.*;<br /> /*<br /> <applet code="AnonymousInnerClassDemo" width=200 height=100><br /> </applet><br /> */<br /> public class AnonymousInnerClassDemo extends Applet {<br /> public void init() {<br /> addMouseListener(new MouseAdapter() {<br /> public void mousePressed(MouseEvent me) {<br /> showStatus("Mouse Pressed");<br /> }<br /> });<br /> }<br /> }<br /> There is one top-level class in this program: AnonymousInnerClassDemo. The init( )<br /> method calls the addMouseListener( ) method. Its argument is an expression that defines<br /> and instantiates an anonymous inner class. Let’s analyze this expression carefully.</div> <div>APPLYING JAVA<br /> Chapter 30: ImageMenu: An Image-Based Web Menu 1055<br /> g.drawImage(off, 0, 0, this);<br /> }<br /> class MyMouseMotionAdapter extends MouseMotionAdapter {<br /> public void mouseDragged(MouseEvent me) {<br /> mouseMoved(me);<br /> }<br /> public void mouseMoved(MouseEvent me) {<br /> int y = me.getY();<br /> selectedCell = (int)(y/(double)d.height*cells);<br /> if (selectedCell != oldCell) {<br /> paint(getGraphics());<br /> showStatus(urlPrefix + url[selectedCell] + urlSuffix);<br /> oldCell = selectedCell;<br /> }<br /> }<br /> }<br /> class MyMouseAdapter extends MouseAdapter {<br /> public void mouseExited(MouseEvent me) {<br /> selectedCell = oldCell = -1;<br /> paint(getGraphics());<br /> showStatus("");<br /> }<br /> public void mouseReleased(MouseEvent me) {<br /> URL u = null;<br /> try {<br /> u = new URL(urlPrefix + url[selectedCell] + urlSuffix);<br /> } catch(Exception e) {<br /> showStatus("error: " + e);<br /> }<br /> }<br /> }<br /> if (me.isShiftDown())<br /> getAppletContext().showDocument(u, "_blank");<br /> else<br /> getAppletContext().showDocument(u, target[selectedCell]);<br /> }</div> <div>This page intentionally left blank.</div> <div>THE JAVA LIBRARY<br /> Chapter 21: Introducing the AWT: Working with Windows, Graphics, and Text 723<br /> // Display font info.<br /> import java.applet.*;<br /> import java.awt.*;<br /> /*<br /> <applet code="FontInfo" width=350 height=60><br /> </applet><br /> */<br /> public class FontInfo extends Applet {<br /> public void paint(Graphics g) {<br /> Font f = g.getFont();<br /> String fontName = f.getName();<br /> String fontFamily = f.getFamily();<br /> int fontSize = f.getSize();<br /> int fontStyle = f.getStyle();<br /> String msg = "Family: " + fontName;<br /> msg += ", Font: " + fontFamily;<br /> msg += ", Size: " + fontSize + ", Style: ";<br /> if((fontStyle & Font.BOLD) == Font.BOLD)<br /> msg += "Bold ";<br /> if((fontStyle & Font.ITALIC) == Font.ITALIC)<br /> msg += "Italic ";<br /> if((fontStyle & Font.PLAIN) == Font.PLAIN)<br /> msg += "Plain ";<br /> }<br /> }<br /> g.drawString(msg, 4, 16);<br /> Managing Text Output Using FontMetrics<br /> As just explained, Java supports a number of fonts. For most fonts, characters are<br /> not all the same dimension—most fonts are proportional. Also, the height of each<br /> character, the length of descenders (the hanging parts of letters, such as y), and the<br /> amount of space between horizontal lines vary from font to font. Further, the point size<br /> of a font can be changed. That these (and other) attributes are variable would not be of<br /> too much consequence except that Java demands that you, the programmer, manually<br /> manage virtually all text output.<br /> Given that the size of each font may differ and that fonts may be changed while<br /> your program is executing, there must be some way to determine the dimensions and<br /> various other attributes of the currently selected font. For example, to write one line of<br /> text after another implies that you have some way of knowing how tall the font is and</div> <div>252 Java™ 2: The Complete Reference<br /> Java run-time system. Any exception that is not caught by your program will ultimately<br /> be processed by the default handler. The default handler displays a string describing<br /> the exception, prints a stack trace from the point at which the exception occurred, and<br /> terminates the program.<br /> Here is the output generated when this example is executed.<br /> java.lang.ArithmeticException: / by zero<br /> at Exc0.main(Exc0.java:4)<br /> Notice how the class name, Exc0; the method name, main; the filename, Exc0.java;<br /> and the line number, 4, are all included in the simple stack trace. Also, notice that the<br /> type of the exception thrown is a subclass of Exception called ArithmeticException,<br /> which more specifically describes what type of error happened. As discussed later in<br /> this chapter, Java supplies several built-in exception types that match the various sorts<br /> of run-time errors that can be generated.<br /> The stack trace will always show the sequence of method invocations that led up to<br /> the error. For example, here is another version of the preceding program that introduces<br /> the same error but in a method separate from main( ):<br /> class Exc1 {<br /> static void subroutine() {<br /> int d = 0;<br /> int a = 10 / d;<br /> }<br /> public static void main(String args[]) {<br /> Exc1.subroutine();<br /> }<br /> }<br /> The resulting stack trace from the default exception handler shows how the entire<br /> call stack is displayed:<br /> java.lang.ArithmeticException: / by zero<br /> at Exc1.subroutine(Exc1.java:4)<br /> at Exc1.main(Exc1.java:7)<br /> As you can see, the bottom of the stack is main’s line 7, which is the call to<br /> subroutine( ), which caused the exception at line 4. The call stack is quite useful for<br /> debugging, because it pinpoints the precise sequence of steps that led to the error.</div> <div>792 Java™ 2: The Complete Reference<br /> Extending Button<br /> The following program creates an applet that displays a button labeled “Test Button”.<br /> When the button is pressed, the string “action event: ” is displayed on the status line<br /> of the applet viewer or browser, followed by a count of the number of button presses.<br /> The program has one top-level class named ButtonDemo2 that extends Applet.A<br /> static integer variable named i is defined and initialized to zero. This records the number<br /> of button pushes. The init( ) method instantiates MyButton and adds it to the applet.<br /> MyButton is an inner class that extends Button. Its constructor uses super to pass<br /> the label of the button to the superclass constructor. It calls enableEvents( ) so that<br /> action events may be received by this object. When an action event is generated,<br /> processActionEvent( ) is called. That method displays a string on the status line and<br /> calls processActionEvent( ) for the superclass. Because MyButton is an inner class, it<br /> has direct access to the showStatus( ) method of ButtonDemo2.<br /> /*<br /> * <applet code=ButtonDemo2 width=200 height=100><br /> * </applet><br /> */<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import java.applet.*;<br /> public class ButtonDemo2 extends Applet {<br /> MyButton myButton;<br /> static int i = 0;<br /> public void init() {<br /> myButton = new MyButton("Test Button");<br /> add(myButton);<br /> }<br /> class MyButton extends Button {<br /> public MyButton(String label) {<br /> super(label);<br /> enableEvents(AWTEvent.ACTION_EVENT_MASK);<br /> }<br /> protected void processActionEvent(ActionEvent ae) {<br /> showStatus("action event: " + i++);<br /> super.processActionEvent(ae);<br /> }<br /> }<br /> }</div> <div>1054 Java™ 2: The Complete Reference<br /> }<br /> urlSuffix = getParameter("urlSuffix");<br /> StringTokenizer st;<br /> st = new StringTokenizer(getParameter("urlList"), "+");<br /> int i=0;<br /> while(st.hasMoreTokens() && i < MAXITEMS)<br /> url[i++] = st.nextToken();<br /> cells = i;<br /> cellH = d.height/cells;<br /> st = new StringTokenizer(getParameter("targetList"), "+");<br /> i=0;<br /> while(st.hasMoreTokens() && i < MAXITEMS)<br /> target[i++] = st.nextToken();<br /> addMouseListener(new MyMouseAdapter());<br /> addMouseMotionListener(new MyMouseMotionAdapter());<br /> private void lateInit() {<br /> off = createImage(d.width, d.height);<br /> try {<br /> img = getImage(getDocumentBase(), getParameter("img"));<br /> MediaTracker t = new MediaTracker(this);<br /> t.addImage(img, 0);<br /> t.waitForID(0);<br /> } catch(Exception e) {<br /> showStatus("error: " + e);<br /> }<br /> }<br /> public void update(Graphics g) {}<br /> public void paint(Graphics g) {<br /> if(off == null)<br /> lateInit();<br /> offg = off.getGraphics();<br /> offg.drawImage(img, 0, 0, this);<br /> if (selectedCell >= 0) {<br /> offg.clipRect(0, selectedCell * cellH, d.width, cellH)<br /> offg.drawImage(img, -d.width, 0, this);<br /> }</div> <div>APPLYING JAVA<br /> Chapter 30: ImageMenu: An Image-Based Web Menu 1049<br /> The ImageMenu applet was inspired by an applet called Navigation, created by<br /> top-notch Java programmer Sean Welch. The difference between Navigation and<br /> ImageMenu is efficiency in bandwidth and applet tag specification. The Navigation<br /> applet uses a source image that is the applet’s width times the number of possible<br /> selections wide to display all of its states. Both applets download a single image, which<br /> is much more efficient over the Internet than loading multiple files. A menu of seven<br /> choices for the Navigation applet (100×140 pixels) would require a source image of<br /> 700×140. The applet described here, ImageMenu, uses a source image that is two times<br /> the applet width, or 200×140. Most web designers hate typing when they don’t have to,<br /> which leads to the second significant difference between Navigation and ImageMenu:<br /> abbreviated applet parameters.<br /> While ImageMenu is many times more efficient, using a smaller source image and<br /> fewer bytes of parameters, Welch’s Navigation has one inimitable trait—it can display<br /> individually selected “states” that bleed over into the space of the next menu item. The<br /> ImageMenu applet requires that each menu item be self-contained in a rectangular area<br /> that cannot overlap with adjacent items. This would prohibit, for example, ascending<br /> letters (like h) from overlapping descending letters (such as j)inthe line above.<br /> The Source Image<br /> While you won’t see the code for Navigation here, looking at its GIF image shows clearly<br /> what it does. The source image for Navigation in Figure 30-2 shows seven columns,<br /> each of which provides a visual representation of a possible selection. However, each<br /> selectable item only has two states, so each row has five redundant copies of the<br /> unselected state.<br /> The source image for ImageMenu is shown in Figure 30-3. Given this image, it is<br /> simple to render any of the seven possible states of a six-choice menu. First, drawImage( )<br /> displays the left half of the source image. This is the state where no items are selected.<br /> If any of the items is selected, then the clipping rectangle is simply set to the bounds of<br /> the selected item, and drawImage( ) is used to display the right-hand side. This will<br /> paint just the selected cell through the clipping rectangle.<br /> Figure 30-2.<br /> The source image for the Navigation applet</div> <div>THE JAVA LIBRARY<br /> Chapter 22: Using AWT Controls, Layout Managers, and Menus 793<br /> Extending Checkbox<br /> The following program creates an applet that displays three check boxes labeled<br /> “Item 1”, “Item 2”, and “Item 3”. When a check box is selected or deselected, a string<br /> containing the name and state of that check box is displayed on the status line of the<br /> applet viewer or browser.<br /> The program has one top-level class named CheckboxDemo2 that extends Applet.<br /> Its init( ) method creates three instances of MyCheckbox and adds these to the applet.<br /> MyCheckbox is an inner class that extends Checkbox. Its constructor uses super to<br /> pass the label of the check box to the superclass constructor. It calls enableEvents( )<br /> so that item events may be received by this object. When an item event is generated,<br /> processItemEvent( ) is called. That method displays a string on the status line and<br /> calls processItemEvent( ) for the superclass.<br /> /*<br /> * <applet code=CheckboxDemo2 width=300 height=100><br /> * </applet><br /> */<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import java.applet.*;<br /> public class CheckboxDemo2 extends Applet {<br /> MyCheckbox myCheckbox1, myCheckbox2, myCheckbox3;<br /> public void init() {<br /> myCheckbox1 = new MyCheckbox("Item 1");<br /> add(myCheckbox1);<br /> myCheckbox2 = new MyCheckbox("Item 2");<br /> add(myCheckbox2);<br /> myCheckbox3 = new MyCheckbox("Item 3");<br /> add(myCheckbox3);<br /> }<br /> class MyCheckbox extends Checkbox {<br /> public MyCheckbox(String label) {<br /> super(label);<br /> enableEvents(AWTEvent.ITEM_EVENT_MASK);<br /> }<br /> protected void processItemEvent(ItemEvent ie) {<br /> showStatus("Checkbox name/state: " + getLabel() +<br /> "/" + getState());<br /> super.processItemEvent(ie);<br /> }</div> <div>882 Java™ 2: The Complete Reference<br /> example, a zzzz pattern can display Pacific Daylight Time, and a zzz pattern can<br /> display PDT.<br /> For numbers, the number of times a pattern letter is repeated determines how<br /> many digits are presented. For example, hh:mm:ss can present 01:51:15, but h:m:s<br /> displays the same time value as 1:51:15.<br /> Finally, M or MM causes the month to be displayed as one or two digits. However,<br /> three or more repetitions of M cause the month to be displayed as a text string.<br /> The following program shows how this class is used:<br /> // Demonstrate SimpleDateFormat.<br /> import java.text.*;<br /> import java.util.*;<br /> public class SimpleDateFormatDemo {<br /> public static void main(String args[]) {<br /> Date date = new Date();<br /> SimpleDateFormat sdf;<br /> sdf = new SimpleDateFormat("hh:mm:ss");<br /> System.out.println(sdf.format(date));<br /> sdf = new SimpleDateFormat("dd MMM yyyy hh:mm:ss zzz");<br /> System.out.println(sdf.format(date));<br /> sdf = new SimpleDateFormat("E MMM dd yyyy");<br /> System.out.println(sdf.format(date));<br /> }<br /> }<br /> Sample output from this program is shown here:<br /> 02:18:23<br /> 08 May 2002 02:18:23 CDT<br /> Wed May 08 2002</div> <div>Contents<br /> xix<br /> Drawing Arcs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 709<br /> Drawing Polygons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 710<br /> Sizing Graphics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 711<br /> Working with Color . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 712<br /> Color Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 713<br /> Setting the Current Graphics Color . . . . . . . . . . . . . . . . . . . . . . . . . 714<br /> A Color Demonstration Applet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 714<br /> Setting the Paint Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 715<br /> Working with Fonts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 717<br /> Determining the Available Fonts . . . . . . . . . . . . . . . . . . . . . . . . . . . 719<br /> Creating and Selecting a Font . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 720<br /> Obtaining Font Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 722<br /> Managing Text Output Using FontMetrics . . . . . . . . . . . . . . . . . . . . . . . . . . . 723<br /> Displaying Multiple Lines of Text . . . . . . . . . . . . . . . . . . . . . . . . . . 725<br /> Centering Text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 727<br /> Multiline Text Alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 728<br /> Exploring Text and Graphics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 733<br /> 22 Using AWT Controls, Layout Managers, and Menus . . . . . . 735<br /> Control Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 736<br /> Adding and Removing Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . 736<br /> Responding to Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 737<br /> Labels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 737<br /> Using Buttons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 739<br /> Handling Buttons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 739<br /> Applying Check Boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 743<br /> Handling Check Boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 743<br /> CheckboxGroup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 745<br /> Choice Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 748<br /> Handling Choice Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 748<br /> Using Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 751<br /> Handling Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 752<br /> Managing Scroll Bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 754<br /> Handling Scroll Bars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 756<br /> Using a TextField . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 758<br /> Handling a TextField . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 759<br /> Using a TextArea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 761<br /> Understanding Layout Managers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 763<br /> FlowLayout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764<br /> BorderLayout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 766<br /> Using Insets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 768<br /> GridLayout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 770<br /> CardLayout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 772<br /> Menu Bars and Menus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 775<br /> Dialog Boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 782<br /> FileDialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 788<br /> Handling Events by Extending AWT Components . . . . . . . . . . . . . . . . . . . . 790<br /> Extending Button . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 792<br /> Extending Checkbox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 793</div> <div>THE JAVA LANGUAGE<br /> Chapter 6: Introducing Classes 153<br /> As you can see, the Stack class defines two data items and three methods. The stack<br /> of integers is held by the array stck. This array is indexed by the variable tos, which<br /> always contains the index of the top of the stack. The Stack( ) constructor initializes<br /> tos to –1, which indicates an empty stack. The method push( ) puts an item on the<br /> stack. To retrieve an item, call pop( ). Since access to the stack is through push( ) and<br /> pop( ), the fact that the stack is held in an array is actually not relevant to using the<br /> stack. For example, the stack could be held in a more complicated data structure, such<br /> as a linked list, yet the interface defined by push( ) and pop( ) would remain the same.<br /> The class TestStack, shown here, demonstrates the Stack class. It creates two<br /> integer stacks, pushes some values onto each, and then pops them off.<br /> class TestStack {<br /> public static void main(String args[]) {<br /> Stack mystack1 = new Stack();<br /> Stack mystack2 = new Stack();<br /> // push some numbers onto the stack<br /> for(int i=0; i<10; i++) mystack1.push(i);<br /> for(int i=10; i<20; i++) mystack2.push(i);<br /> // pop those numbers off the stack<br /> System.out.println("Stack in mystack1:");<br /> for(int i=0; i<10; i++)<br /> System.out.println(mystack1.pop());<br /> }<br /> }<br /> System.out.println("Stack in mystack2:");<br /> for(int i=0; i<10; i++)<br /> System.out.println(mystack2.pop());<br /> This program generates the following output:<br /> Stack in mystack1:<br /> 9<br /> 8<br /> 7<br /> 6<br /> 5<br /> 4<br /> 3<br /> 2</div> <div>798 Java™ 2: The Complete Reference<br /> Exploring the Controls, Menus, and Layout<br /> Managers<br /> This chapter has discussed the classes that comprise the AWT controls, menus, and<br /> layout managers. However, the AWT provides a rich programming environment that<br /> you will want to continue exploring on your own. Here are some suggestions:<br /> ■ Try nesting a canvas inside an applet panel.<br /> ■ Explore the FileDialog component.<br /> ■ Experiment with manual positioning of components by using setBounds( ).<br /> ■ Try nesting controls within panels to gain more control over layouts.<br /> ■ Create your own layout manager by implementing the LayoutManager<br /> interface.<br /> ■ Explore PopupMenu.<br /> The more you know about the AWT components, the more control you will have over<br /> the look, feel, and performance of your applets and applications.<br /> In the next chapter, we will examine one more of the AWT’s classes: Image. This<br /> class is used to support imaging and animation.</div> <div>THE JAVA LIBRARY<br /> Chapter 16: java.util Part 2: More Utility Classes 513<br /> Method<br /> boolean equals(Object date)<br /> long getTime( )<br /> int hashCode( )<br /> void setTime(long time)<br /> String toString( )<br /> Description<br /> Returns true if the invoking Date object contains<br /> the same time and date as the one specified by date.<br /> Otherwise, it returns false.<br /> Returns the number of milliseconds that have<br /> elapsed since January 1, 1970.<br /> Returns a hash code for the invoking object.<br /> Sets the time and date as specified by time, which<br /> represents an elapsed time in milliseconds from<br /> midnight, January 1, 1970.<br /> Converts the invoking Date object into a string and<br /> returns the result.<br /> Table 16-3.<br /> The Nondeprecated Methods Defined by Date (continued)<br /> As you can see by examining Table 16-3, the Date features do not allow you to<br /> obtain the individual components of the date or time. As the following program<br /> demonstrates, you can only obtain the date and time in terms of milliseconds or in its<br /> default string representation as returned by toString( ). To obtain more-detailed<br /> information about the date and time, you will use the Calendar class.<br /> // Show date and time using only Date methods.<br /> import java.util.Date;<br /> class DateDemo {<br /> public static void main(String args[]) {<br /> // Instantiate a Date object<br /> Date date = new Date();<br /> // display time and date using toString()<br /> System.out.println(date);<br /> // Display number of milliseconds since midnight, January 1, 1970 GMT</div> <div>THE JAVA LANGUAGE<br /> Chapter 8: Inheritance 191<br /> B subOb = new B();<br /> // The superclass may be used by itself.<br /> superOb.i = 10;<br /> superOb.j = 20;<br /> System.out.println("Contents of superOb: ");<br /> superOb.showij();<br /> System.out.println();<br /> /* The subclass has access to all public members of<br /> its superclass. */<br /> subOb.i = 7;<br /> subOb.j = 8;<br /> subOb.k = 9;<br /> System.out.println("Contents of subOb: ");<br /> subOb.showij();<br /> subOb.showk();<br /> System.out.println();<br /> }<br /> }<br /> System.out.println("Sum of i, j and k in subOb:");<br /> subOb.sum();<br /> The output from this program is shown here:<br /> Contents of superOb:<br /> i and j: 10 20<br /> Contents of subOb:<br /> i and j: 7 8<br /> k: 9<br /> Sum of i, j and k in subOb:<br /> i+j+k: 24<br /> As you can see, the subclass B includes all of the members of its superclass, A. This<br /> is why subOb can access i and j and call showij( ). Also, inside sum( ), i and j can be<br /> referred to directly, as if they were part of B.</div> <div>862 Java™ 2: The Complete Reference<br /> // A simple pattern matching demo.<br /> import java.util.regex.*;<br /> class RegExpr {<br /> public static void main(String args[]) {<br /> Pattern pat;<br /> Matcher mat;<br /> boolean found;<br /> pat = Pattern.compile("Java");<br /> mat = pat.matcher("Java");<br /> found = mat.matches(); // check for a match<br /> System.out.println("Testing Java against Java.");<br /> if(found) System.out.println("Matches");<br /> else System.out.println("No Match");<br /> System.out.println();<br /> System.out.println("Testing Java against Java 2.");<br /> mat = pat.matcher("Java 2"); // create a new matcher<br /> found = mat.matches(); // check for a match<br /> }<br /> }<br /> if(found) System.out.println("Matches");<br /> else System.out.println("No Match");<br /> The output from the program is shown here:<br /> Testing Java against Java.<br /> Matches<br /> Testing Java against Java 2.<br /> No Match<br /> Let’s look closely at this program. The program begins by creating the pattern that<br /> contains the sequence “Java”. Next, a Matcher is created for that pattern that has the<br /> input sequence “Java”. Then, the matches( ) method is called to determine if the input<br /> sequence matches the pattern. Because, the sequence and the pattern are the same,</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 28: Migrating from C++ to Java 995<br /> Converting C++ Abstract Classes into<br /> Java Interfaces<br /> One of the most innovative aspects of Java is the interface. As explained earlier in this<br /> book, an interface specifies the form of its various methods without specifying any<br /> implementation details. Each class that implements an interface does so by creating<br /> the actual methods declared by the interface. Thus, in Java an interface is the means<br /> by which you can define the general form of a class while ensuring that all specific<br /> versions of the class conform to the same set of rules. The interface is one of the ways<br /> that Java provides support for polymorphism.<br /> In C++, there is no direct parallel to the interface. Instead, in C++, if you wish to<br /> define the form of a class without defining implementation details, you must do so by<br /> using an abstract class. Abstract classes in C++ are similar to abstract classes in Java:<br /> they do not contain a full set of implementation details. In C++, an abstract class contains<br /> at least one pure virtual function. A pure virtual function defines no implementation; it<br /> only defines the function prototype. Thus, a pure virtual function in C++ is essentially<br /> the same as an abstract method in Java. In C++, abstract classes serve a function similar<br /> to interfaces in Java. For this reason, they are one of the items that you will want to<br /> watch for when converting code to Java. While not all C++ abstract classes can be<br /> converted into Java interfaces, many can. Let’s look at two examples.<br /> Here is a short C++ program that uses an abstract class called IntList to define the<br /> form of an integer list. An implementation of this class is created by IntArray, which<br /> uses an array to implement a list of integers.<br /> // A C++-style abstract class and its implementation.<br /> #include <iostream><br /> #include <cstdlib><br /> using namespace std;<br /> // An abstract class that defines the form of an integer list.<br /> class IntList {<br /> public:<br /> virtual int getNext() = 0; // pure virtual functions<br /> virtual void putOnList(int i) = 0;<br /> };<br /> // Create an implementation of an integer list.<br /> class IntArray : public IntList {<br /> int storage[100];<br /> int putIndex, getIndex;<br /> public:<br /> IntArray() {<br /> putIndex = 0;<br /> getIndex = 0;</div> <div>Chapter 11<br /> Multithreaded<br /> Programming<br /> 273</div> <div>824 Java™ 2: The Complete Reference<br /> Figure 23-7.<br /> Sample output from TileImage<br /> RGBImageFilters, and two more classes—Blur and Sharpen—which do more<br /> complicated “convolution” filters that change pixel data based on the pixels<br /> surrounding each pixel of source data. Blur and Sharpen are subclasses of an<br /> abstract helper class called Convolver. Let’s look at each part of our example.<br /> ImageFilterDemo.java<br /> The ImageFilterDemo class is the applet framework for our sample image filters. It<br /> employs a simple BorderLayout, with a Panel at the South position to hold the buttons<br /> that will represent each filter. A Label object occupies the North slot for informational<br /> messages about filter progress. The Center is where the image (which is encapsulated in<br /> the LoadedImage Canvas subclass, described later) is put. We parse the buttons/filters<br /> out of the filters <param> tag, separating them with +’s using a StringTokenizer.<br /> The actionPerformed( ) method is interesting because it uses the label from a<br /> button as the name of a filter class that it tries to load with (PlugInFilter)<br /> Class.forName(a).newInstance( ). This method is robust and takes appropriate action<br /> if the button does not correspond to a proper class that implements PlugInFilter.</div> <div>THE JAVA LIBRARY<br /> Chapter 15: java.util Part 1: The Collections Framework 487<br /> Method<br /> void insertElementAt(Object element,<br /> int index)<br /> boolean isEmpty( )<br /> Object lastElement( )<br /> int lastIndexOf(Object element)<br /> int lastIndexOf(Object element,<br /> int start)<br /> void removeAllElements( )<br /> boolean removeElement(Object element)<br /> void removeElementAt(int index)<br /> void setElementAt(Object element,<br /> int index)<br /> void setSize(int size)<br /> Description<br /> Adds element to the vector at the<br /> location specified by index.<br /> Returns true if the vector is empty<br /> and returns false if it contains one<br /> or more elements.<br /> Returns the last element in the<br /> vector.<br /> Returns the index of the last<br /> occurrence of element. If the object<br /> is not in the vector, –1 is returned.<br /> Returns the index of the last<br /> occurrence of element before start.<br /> If the object is not in that portion<br /> of the vector, –1 is returned.<br /> Empties the vector. After this<br /> method executes, the size of the<br /> vector is zero.<br /> Removes element from the vector.<br /> If more than one instance of the<br /> specified object exists in the<br /> vector, then it is the first one that<br /> is removed. Returns true if<br /> successful and false if the object is<br /> not found.<br /> Removes the element at the<br /> location specified by index.<br /> The location specified by index is<br /> assigned element.<br /> Sets the number of elements in the<br /> vector to size. If the new size is<br /> less than the old size, elements are<br /> lost. If the new size is larger than<br /> the old size, null elements are<br /> added.<br /> Table 15-10.<br /> The Methods Defined by Vector (continued)</div> <div>THE JAVA LANGUAGE<br /> Chapter 9: Packages and Interfaces 235<br /> }<br /> test.show(); // you may also call show()<br /> }<br /> As an experiment, remove the public specifier from the Balance class and then try<br /> compiling TestBalance. As explained, errors will result.<br /> Interfaces<br /> Using the keyword interface, you can fully abstract a class’ interface from its implementation.<br /> That is, using interface, you can specify what a class must do, but not how<br /> it does it. Interfaces are syntactically similar to classes, but they lack instance variables,<br /> and their methods are declared without any body. In practice, this means that you can<br /> define interfaces which don’t make assumptions about how they are implemented.<br /> Once it is defined, any number of classes can implement an interface. Also, one class<br /> can implement any number of interfaces.<br /> To implement an interface, a class must create the complete set of methods defined<br /> by the interface. However, each class is free to determine the details of its own<br /> implementation. By providing the interface keyword, Java allows you to fully utilize<br /> the “one interface, multiple methods” aspect of polymorphism.<br /> Interfaces are designed to support dynamic method resolution at run time.<br /> Normally, in order for a method to be called from one class to another, both classes<br /> need to be present at compile time so the Java compiler can check to ensure that the<br /> method signatures are compatible. This requirement by itself makes for a static and<br /> nonextensible classing environment. Inevitably in a system like this, functionality gets<br /> pushed up higher and higher in the class hierarchy so that the mechanisms will be<br /> available to more and more subclasses. Interfaces are designed to avoid this problem.<br /> They disconnect the definition of a method or set of methods from the inheritance<br /> hierarchy. Since interfaces are in a different hierarchy from classes, it is possible for<br /> classes that are unrelated in terms of the class hierarchy to implement the same<br /> interface. This is where the real power of interfaces is realized.<br /> Interfaces add most of the functionality that is required for many applications which<br /> would normally resort to using multiple inheritance in a language such as C++.<br /> Defining an Interface<br /> An interface is defined much like a class. This is the general form of an interface:<br /> access interface name {<br /> return-type method-name1(parameter-list);<br /> return-type method-name2(parameter-list);<br /> type final-varname1 = value;</div> <div>224 Java™ 2: The Complete Reference<br /> This chapter examines two of Java’s most innovative features: packages and<br /> interfaces. Packages are containers for classes that are used to keep the class name<br /> space compartmentalized. For example, a package allows you to create a class<br /> named List, which you can store in your own package without concern that it will<br /> collide with some other class named List stored elsewhere. Packages are stored in a<br /> hierarchical manner and are explicitly imported into new class definitions.<br /> In previous chapters you have seen how methods define the interface to the data in<br /> a class. Through the use of the interface keyword, Java allows you to fully abstract the<br /> interface from its implementation. Using interface, you can specify a set of methods<br /> which can be implemented by one or more classes. The interface, itself, does not<br /> actually define any implementation. Although they are similar to abstract classes,<br /> interfaces have an additional capability: A class can implement more than one<br /> interface. By contrast, a class can only inherit a single superclass (abstract or<br /> otherwise).<br /> Packages and interfaces are two of the basic components of a Java program. In<br /> general, a Java source file can contain any (or all) of the following four internal parts:<br /> ■ A single package statement (optional)<br /> ■ Any number of import statements (optional)<br /> ■ A single public class declaration (required)<br /> ■ Any number of classes private to the package (optional)<br /> Only one of these—the single public class declaration—has been used in the<br /> examples so far. This chapter will explore the remaining parts.<br /> Packages<br /> In the preceding chapters, the name of each example class was taken from the same<br /> name space. This means that a unique name had to be used for each class to avoid<br /> name collisions. After a while, without some way to manage the name space, you<br /> could run out of convenient, descriptive names for individual classes. You also need<br /> some way to be assured that the name you choose for a class will be reasonably<br /> unique and not collide with class names chosen by other programmers. (Imagine<br /> a small group of programmers fighting over who gets to use the name “Foobar” as a<br /> class name. Or, imagine the entire Internet community arguing over who first named<br /> a class “Espresso.”) Thankfully, Java provides a mechanism for partitioning the class<br /> name space into more manageable chunks. This mechanism is the package. The<br /> package is both a naming and a visibility control mechanism. You can define classes<br /> inside a package that are not accessible by code outside that package. You can also<br /> define class members that are only exposed to other members of the same package.<br /> This allows your classes to have intimate knowledge of each other, but not expose<br /> that knowledge to the rest of the world.</div> <div>1006 Java™ 2: The Complete Reference<br /> }<br /> }<br /> else {<br /> System.out.println("Error -- can't construct");<br /> System.exit(1);<br /> }<br /> // finalization<br /> protected void finalize() {<br /> count--;<br /> }<br /> static void f()<br /> {<br /> X ob = new X(); // allocate an object<br /> // destruct on way out<br /> }<br /> public static void main(String args[]) {<br /> int i;<br /> }<br /> }<br /> for(i=0; i < (MAX*2); i++) {<br /> f();<br /> System.out.println("Current count is: " + count);<br /> }<br /> This program will fail after five calls to f( ), as this output shows:<br /> Current count is: 1<br /> Current count is: 2<br /> Current count is: 3<br /> Current count is: 4<br /> Current count is: 5<br /> Error — can’t construct<br /> The reason the program fails is that garbage collection does not occur each time f( )<br /> returns. Thus, finalize( ) is not invoked, and the value of count is not decremented.<br /> After five calls to the method, count reaches its maximum value and the program fails.</div> <div>532 Java™ 2: The Complete Reference<br /> Method<br /> boolean cancel( )<br /> abstract void run( )<br /> long scheduledExecutionTime( )<br /> Description<br /> Terminates the task. It returns true if<br /> an execution of the task is prevented.<br /> Otherwise, false is returned.<br /> Contains the code for the timer task.<br /> Returns the time at which the last<br /> execution of the task was scheduled to<br /> have occurred.<br /> Table 16-8.<br /> The Methods Defined by TimerTask<br /> Once a task has been created, it is scheduled for execution by an object of type<br /> Timer. The constructors for Timer are shown here.<br /> Timer( )<br /> Timer(boolean DThread)<br /> The first version creates a Timer object that runs as a normal thread. The second<br /> uses a daemon thread if DThread is true. A daemon thread will execute only as long as<br /> the rest of the program continues to execute. The methods defined by Timer are shown<br /> in Table 16-9.<br /> Method<br /> void cancel( )<br /> void schedule(TimerTask TTask,<br /> long wait)<br /> void schedule(TimerTask TTask,<br /> long wait, long repeat)<br /> Description<br /> Cancels the timer thread.<br /> TTask is scheduled for execution after<br /> the period passed in wait has elapsed.<br /> The wait parameter is specified in<br /> milliseconds.<br /> TTask is scheduled for execution after<br /> the period passed in wait has elapsed.<br /> The task is then executed repeatedly at<br /> the interval specified by repeat. Both<br /> wait and repeat are specified in<br /> milliseconds.<br /> Table 16-9.<br /> The Methods Defined by Timer</div> <div>510 Java™ 2: The Complete Reference<br /> Method<br /> void set(int index, boolean v)<br /> void set(int startIndex,<br /> int endIndex)<br /> void set(int startIndex,<br /> int endIndex, boolean v)<br /> int size( )<br /> String toString( )<br /> void xor(BitSet bitSet)<br /> Description<br /> Sets the bit specified by index to the value<br /> passed in v. true sets the bit, false clears the<br /> bit. (Added by Java 2, version 1.4)<br /> Sets the bits from startIndex to endIndex–1.<br /> (Added by Java 2, version 1.4)<br /> Sets the bits from startIndex to endIndex–1, to<br /> the value passed in v. true sets the bits, false<br /> clears the bits. (Added by Java 2, version 1.4)<br /> Returns the number of bits in the invoking<br /> BitSet object.<br /> Returns the string equivalent of the invoking<br /> BitSet object.<br /> XORs the contents of the invoking BitSet<br /> object with that specified by bitSet. The result<br /> is placed into the invoking object.<br /> Table 16-2.<br /> The Methods Defined by BitSet (continued)<br /> Here is an example that demonstrates BitSet:<br /> // BitSet Demonstration.<br /> import java.util.BitSet;<br /> class BitSetDemo {<br /> public static void main(String args[]) {<br /> BitSet bits1 = new BitSet(16);<br /> BitSet bits2 = new BitSet(16);<br /> // set some bits<br /> for(int i=0; i<16; i++) {<br /> if((i%2) == 0) bits1.set(i);<br /> if((i%5) != 0) bits2.set(i);<br /> }</div> <div>APPLYING JAVA<br /> Chapter 29: The DynamicBillboard Applet 1043<br /> if(unroll_amount[c] > 1) {<br /> offset[1] = 3;<br /> }<br /> if(unroll_amount[c] > 2) {<br /> offset[unroll_amount[c] - 1] = 2;<br /> }<br /> if(unroll_amount[c] > 3) {<br /> offset[unroll_amount[c] - 2] = 3;<br /> }<br /> int offset_index = 0;<br /> int end_location = location + unroll_amount[c] * cell_w;<br /> for(int p = location; p < end_location; p += cell_w) {<br /> }<br /> System.arraycopy(next_pixels,<br /> p - y_flip + offset[offset_index],<br /> work_pixels,<br /> p, cell_w - offset[offset_index]);<br /> System.arraycopy(fill_pixels, 0,<br /> work_pixels,<br /> p + cell_w - offset[offset_index],<br /> offset[offset_index]);<br /> ++offset_index;<br /> y_flip += cell_w + cell_w;<br /> }<br /> }<br /> for(int x = location + cell_w - 1; x > location; --x) {<br /> work_pixels[x] |= 0xFFAAAAAA;<br /> work_pixels[x + unroll_amount[c]] &= 0xFF555555;<br /> }<br /> Here is what the unroll transition looks like before, during, and after:</div> <div>250 Java™ 2: The Complete Reference<br /> This chapter examines Java’s exception-handling mechanism. An exception is an<br /> abnormal condition that arises in a code sequence at run time. In other words,<br /> an exception is a run-time error. In computer languages that do not support<br /> exception handling, errors must be checked and handled manually—typically through<br /> the use of error codes, and so on. This approach is as cumbersome as it is troublesome.<br /> Java’s exception handling avoids these problems and, in the process, brings run-time<br /> error management into the object-oriented world.<br /> For the most part, exception handling has not changed since the original version<br /> of Java. However, Java 2, version 1.4 has added a new subsystem called the chained<br /> exception facility. This feature is described near the end of this chapter.<br /> Exception-Handling Fundamentals<br /> A Java exception is an object that describes an exceptional (that is, error) condition<br /> that has occurred in a piece of code. When an exceptional condition arises, an object<br /> representing that exception is created and thrown in the method that caused the error.<br /> That method may choose to handle the exception itself, or pass it on. Either way, at<br /> some point, the exception is caught and processed. Exceptions can be generated by the<br /> Java run-time system, or they can be manually generated by your code. Exceptions<br /> thrown by Java relate to fundamental errors that violate the rules of the Java language<br /> or the constraints of the Java execution environment. Manually generated exceptions<br /> are typically used to report some error condition to the caller of a method.<br /> Java exception handling is managed via five keywords: try, catch, throw, throws,<br /> and finally. Briefly, here is how they work. Program statements that you want to<br /> monitor for exceptions are contained within a try block. If an exception occurs within<br /> the try block, it is thrown. Your code can catch this exception (using catch) and handle<br /> it in some rational manner. System-generated exceptions are automatically thrown by<br /> the Java run-time system. To manually throw an exception, use the keyword throw.<br /> Any exception that is thrown out of a method must be specified as such by a throws<br /> clause. Any code that absolutely must be executed before a method returns is put in<br /> a finally block.<br /> This is the general form of an exception-handling block:<br /> try {<br /> // block of code to monitor for errors<br /> }<br /> catch (ExceptionType1 exOb) {<br /> // exception handler for ExceptionType1<br /> }<br /> catch (ExceptionType2 exOb) {<br /> // exception handler for ExceptionType2<br /> }<br /> // ...</div> <div>Preface<br /> The past few years document the following fact: The Web has irrevocably recast<br /> the face of computing and programmers unwilling to master its environment will<br /> be left behind.<br /> The preceding is a strong statement. It is also true. More and more, applications<br /> must interface to the Web. It no longer matters much what the application is, near<br /> universal Web access is dragging, pushing, and coaxing programmers to program for<br /> the online world, and Java is the language that many will use to do it. Frankly, fluency<br /> in Java is no longer an option for the professional programmer, it is a requirement. This<br /> book will help you acquire it.<br /> Aside from being the preeminent language of the Internet, Java is important for<br /> another reason: it has altered the course of computer language development. Many of<br /> the features first mainstreamed by Java are now finding their way into other languages.<br /> For example, the new C# language is strongly influenced by Java. Knowledge of Java<br /> opens the door to the latest innovations in programming. Put directly, Java is one of the<br /> world’s most important computer languages.<br /> xxv</div> <div>834 Java™ 2: The Complete Reference<br /> }<br /> }<br /> }<br /> pix = model.getRGB(pixels[sx++]);<br /> if((pix & 0xff000000) == 0)<br /> pix = 0x00ffffff;<br /> imgpixels[y*width+x] = pix;<br /> }<br /> sy += scansize;<br /> Blur.java<br /> The Blur filter is a subclass of Convolver and simply runs through every pixel in the<br /> source image array, imgpixels, and computes the average of the 3×3 box surrounding<br /> it. The corresponding output pixel in newimgpixels is that average value.<br /> public class Blur extends Convolver {<br /> public void convolve() {<br /> for(int y=1; y<height-1; y++) {<br /> for(int x=1; x<width-1; x++) {<br /> int rs = 0;<br /> int gs = 0;<br /> int bs = 0;<br /> for(int k=-1; k<=1; k++) {<br /> for(int j=-1; j<=1; j++) {<br /> int rgb = imgpixels[(y+k)*width+x+j];<br /> int r = (rgb >> 16) & 0xff;<br /> int g = (rgb >> 8) & 0xff;<br /> int b = rgb & 0xff;<br /> rs += r;<br /> gs += g;<br /> bs += b;<br /> }<br /> }<br /> rs /= 9;<br /> gs /= 9;<br /> bs /= 9;<br /> newimgpixels[y*width+x] = (0xff000000 |</div> <div>1012 Java™ 2: The Complete Reference<br /> Robert Temple is a software engineer who has designed several highly used applets.<br /> His work includes the ESPNET SportsZone “HitCharts” and “Batter vs. Pitcher”<br /> applets. One of his most impressive applets is DynamicBillboard, which he wrote<br /> while he was at Embry-Riddle Aeronautical University in Florida.<br /> The DynamicBillboard applet displays a sequence of images by repeatedly<br /> changing the image on the screen to another after a period of time. The transition<br /> between one image and the next is done with one of a variety of special effects. One<br /> example of a transition is the SmashTransition, where the new image drops down<br /> from above the old image and appears to smash the old image out of place. The applet<br /> links to other pages through a URL associated with each image. When the user presses<br /> the mouse button with the cursor over the applet, the browser will go to the new page<br /> associated with the current image. The DynamicBillboard applet provides web sites<br /> with an elegant way to rotate ads, banners, or billboards on a single static page.<br /> Robert has included many interesting optimizations. This applet would not be<br /> functional without the careful changes that he crafted. There are enough tips and tricks<br /> in this source code to help you make your applets really fly.<br /> The APPLET Tag<br /> The APPLET tag for DynamicBillboard is fairly easy to configure. You name the main<br /> class in the code parameter and specify the width and height, as with most applets:<br /> <applet code=DynamicBillboard width=392 height=72><br /> There are several parameters that must be specified for the applet to function<br /> properly. Without them the applet does nothing. Also, you will notice that if you make<br /> any mistakes naming files and such, the behavior is a little unfriendly: either nothing<br /> happens or some of your billboards will be blank. The following parameters are<br /> specified as:<br /> <param name=parameter_name value="your value here"><br /> ■ bgcolor This parameter is used to set the background color of the applet<br /> before the first image loads. You can use this to get rid of the gray applet<br /> square quickly.<br /> ■ delay This parameter specifies the number of milliseconds between<br /> each billboard. Typically, it’s a number like 5000 or 10000, meaning five or<br /> ten seconds.</div> <div>754 Java™ 2: The Complete Reference<br /> }<br /> }<br /> g.drawString(msg, 6, 120);<br /> msg = "Current Browser: ";<br /> msg += browser.getSelectedItem();<br /> g.drawString(msg, 6, 140);<br /> Sample output generated by the ListDemo applet is shown in Figure 22-5. Notice that<br /> the browser list has a scroll bar, since all of the items won’t fit in the number of rows<br /> specified when it is created.<br /> Managing Scroll Bars<br /> Scroll bars are used to select continuous values between a specified minimum and<br /> maximum. Scroll bars may be oriented horizontally or vertically. A scroll bar is actually<br /> a composite of several individual parts. Each end has an arrow that you can click to move<br /> the current value of the scroll bar one unit in the direction of the arrow. The current value<br /> of the scroll bar relative to its minimum and maximum values is indicated by the slider box<br /> (or thumb) for the scroll bar. The slider box can be dragged by the user to a new position.<br /> The scroll bar will then reflect this value. In the background space on either side of the<br /> Figure 22-5.<br /> Sample output from the ListDemo applet</div> <div>THE JAVA LIBRARY<br /> Chapter 15: java.util Part 1: The Collections Framework 495<br /> Method<br /> void clear( )<br /> Object clone( )<br /> boolean contains(Object value)<br /> boolean containsKey(Object key)<br /> boolean containsValue(Object value)<br /> Enumeration elements( )<br /> Object get(Object key)<br /> boolean isEmpty( )<br /> Enumeration keys( )<br /> Object put(Object key, Object value)<br /> void rehash( )<br /> Description<br /> Resets and empties the hash table.<br /> Returns a duplicate of the invoking object.<br /> Returns true if some value equal to value<br /> exists within the hash table. Returns false<br /> if the value isn’t found.<br /> Returns true if some key equal to key<br /> exists within the hash table. Returns false<br /> if the key isn’t found.<br /> Returns true if some value equal to value<br /> exists within the hash table. Returns false<br /> if the value isn’t found. (A non-Map<br /> method added by Java 2, for consistency.)<br /> Returns an enumeration of the values<br /> contained in the hash table.<br /> Returns the object that contains the value<br /> associated with key. If key is not in the<br /> hash table, a null object is returned.<br /> Returns true if the hash table is empty;<br /> returns false if it contains at least one key.<br /> Returns an enumeration of the keys<br /> contained in the hash table.<br /> Inserts a key and a value into the hash<br /> table. Returns null if key isn’t already in<br /> the hash table; returns the previous value<br /> associated with key if key is already in the<br /> hash table.<br /> Increases the size of the hash table and<br /> rehashes all of its keys.<br /> Table 15-13.<br /> The Legacy Methods Defined by Hashtable</div> <div>This page intentionally left blank.</div> <div>THE JAVA LIBRARY<br /> Chapter 22: Using AWT Controls, Layout Managers, and Menus 769<br /> The getInsets( ) method has this general form:<br /> Insets getInsets( )<br /> When overriding one of these methods, you must return a new Insets object that contains<br /> the inset spacing you desire.<br /> Here is the preceding BorderLayout example modified so that it insets its components<br /> ten pixels from each border. The background color has been set to cyan to help make the<br /> insets more visible.<br /> // Demonstrate BorderLayout with insets.<br /> import java.awt.*;<br /> import java.applet.*;<br /> import java.util.*;<br /> /*<br /> <applet code="InsetsDemo" width=400 height=200><br /> </applet><br /> */<br /> public class InsetsDemo extends Applet {<br /> public void init() {<br /> // set background color so insets can be easily seen<br /> setBackground(Color.cyan);<br /> setLayout(new BorderLayout());<br /> add(new Button("This is across the top."),<br /> BorderLayout.NORTH);<br /> add(new Label("The footer message might go here."),<br /> BorderLayout.SOUTH);<br /> add(new Button("Right"), BorderLayout.EAST);<br /> add(new Button("Left"), BorderLayout.WEST);<br /> String msg = "The reasonable man adapts " +<br /> "himself to the world;\n" +<br /> "the unreasonable one persists in " +<br /> "trying to adapt the world to himself.\n" +<br /> "Therefore all progress depends " +<br /> "on the unreasonable man.\n\n" +<br /> " - George Bernard Shaw\n\n";<br /> }<br /> add(new TextArea(msg), BorderLayout.CENTER);</div> <div>THE JAVA LIBRARY<br /> Chapter 24: New I/O, Regular Expressions, and Other Packages 861<br /> You can replace all occurrences of a matching sequence with another sequence by<br /> calling replaceAll( ), shown here:<br /> String replaceAll(String newStr)<br /> Here, newStr specifies the new character sequence that will replace the ones that match<br /> the pattern. The updated input sequence is returned as a string.<br /> Regular Expression Syntax<br /> Before demonstrating Pattern and Matcher it is necessary to explain how to construct a<br /> regular expression. The syntax and rules that define a regular expression are similar to<br /> those used by Perl 5. Although no rule is complicated by itself, there are a large number<br /> of them, and a complete discussion is beyond the scope of this chapter. However, a few<br /> of the more commonly used constructs are described here.<br /> In general, a regular expression is comprised of normal characters, character classes<br /> (sets of characters), wildcard characters, and quantifiers. A normal character is matched<br /> as-is. Thus, if a pattern consists of “xy”, then the only input sequence that will match it<br /> is “xy”. Characters such as newline and tab are specified using the standard escape<br /> sequences, which begin with a \. For example, a newline is specified by \n.Inthe language<br /> of regular expressions, a normal character is also called a literal.<br /> A character class is a set of characters. A character class is specified by putting the<br /> characters in the class between brackets. For example, the class [wxyz] matches w, x, y,<br /> or z. To specify an inverted set, precede the characters with a ^. For example, [^wxyz]<br /> matches any character except w, x, y, or z. You can specify a range of characters using a<br /> hypen. For example, to specify a character class that will match the digits 1 through 9<br /> use [1-9].<br /> The wildcard character is the . (dot) and it matches any character. Thus, a pattern that<br /> consists of “.” will match these (and other) input seqeunces: “A”, “a”, “x”, and so on.<br /> A quantifier determines how many times an expression is matched. The quantifiers<br /> are shown here:<br /> + Match one or more.<br /> * Match zero or more.<br /> ? Match zero or one.<br /> For example, the pattern “x+” will match “x”, “xx”, and “xxx”, among others.<br /> Demonstrating Pattern Matching<br /> The best way to understand how regular expression pattern matching operates is to work<br /> through some examples. The first, shown here, looks for a match with a literal pattern.</div> <div>THE JAVA LANGUAGE<br /> Chapter 1: The Genesis of Java 15<br /> Distributed<br /> Java is designed for the distributed environment of the Internet, because it handles<br /> TCP/IP protocols. In fact, accessing a resource using a URL is not much different<br /> from accessing a file. The original version of Java (Oak) included features for intraaddress-space<br /> messaging. This allowed objects on two different computers to execute<br /> procedures remotely. Java revived these interfaces in a package called Remote Method<br /> Invocation (RMI). This feature brings an unparalleled level of abstraction to client/<br /> server programming.<br /> Dynamic<br /> Java programs carry with them substantial amounts of run-time type information that<br /> is used to verify and resolve accesses to objects at run time. This makes it possible to<br /> dynamically link code in a safe and expedient manner. This is crucial to the robustness<br /> of the applet environment, in which small fragments of bytecode may be dynamically<br /> updated on a running system.<br /> The Continuing Revolution<br /> The initial release of Java was nothing short of revolutionary, but it did not mark the<br /> end of Java’s era of rapid innovation. Unlike most other software systems that usually<br /> settle into a pattern of small, incremental improvements, Java continued to evolve at<br /> an explosive pace. Soon after the release of Java 1.0, the designers of Java had already<br /> created Java 1.1. The features added by Java 1.1 were more significant and substantial<br /> than the increase in the minor revision number would have you think. Java 1.1 added<br /> many new library elements, redefined the way events are handled by applets, and<br /> reconfigured many features of the 1.0 library. It also deprecated (rendered obsolete)<br /> several features originally defined by Java 1.0. Thus, Java 1.1 both added and<br /> subtracted attributes from its original specification.<br /> The next major release of Java was Java 2. Java 2 was a watershed event, marking<br /> the beginning of the “modern age” of this rapidly evolving language! The first release<br /> of Java 2 carried the version number 1.2. It may seem odd that the first release of Java 2<br /> used the 1.2 version number. The reason is that it originally referred to the version of<br /> the Java libraries, but it was generalized to refer to the entire release, itself. Java 2<br /> added support for a number of new features, such as Swing and the Collections<br /> framework, and it enhanced the Java Virtual Machine and various programming tools.<br /> Java 2 also contained a few deprecations. The most important affected the Thread class<br /> in which the methods suspend( ), resume( ), and stop( ) were deprecated.<br /> The next release of Java was Java 2, version 1.3. This version of Java was the first<br /> major upgrade to the original Java 2 release. For the most part it added to existing<br /> functionality and “tightened up” the development environment. In general, programs<br /> written for version 1.2 and those written for version 1.3 are source-code compatible.<br /> Although version 1.3 contained a smaller set of changes than the preceding three major<br /> releases, it was nevertheless important.</div> <div>570 Java™ 2: The Complete Reference<br /> }<br /> }<br /> f.mark(32);<br /> marked = true;<br /> } else {<br /> marked = false;<br /> }<br /> break;<br /> case ';':<br /> if (marked) {<br /> marked = false;<br /> System.out.print("(c)");<br /> } else<br /> System.out.print((char) c);<br /> break;<br /> case ' ':<br /> if (marked) {<br /> marked = false;<br /> f.reset();<br /> System.out.print("&");<br /> } else<br /> System.out.print((char) c);<br /> break;<br /> default:<br /> if (!marked)<br /> System.out.print((char) c);<br /> break;<br /> }<br /> }<br /> BufferedWriter<br /> A BufferedWriter is a Writer that adds a flush( ) method that can be used to ensure<br /> that data buffers are physically written to the actual output stream. Using a<br /> BufferedWriter can increase performance by reducing the number of times data is<br /> actually physically written to the output stream.<br /> A BufferedWriter has these two constructors:<br /> BufferedWriter(Writer outputStream)<br /> BufferedWriter(Writer outputStream, int bufSize)</div> <div>246 Java™ 2: The Complete Reference<br /> Interfaces Can Be Extended<br /> One interface can inherit another by use of the keyword extends. The syntax is the<br /> same as for inheriting classes. When a class implements an interface that inherits<br /> another interface, it must provide implementations for all methods defined within<br /> the interface inheritance chain. Following is an example:<br /> // One interface can extend another.<br /> interface A {<br /> void meth1();<br /> void meth2();<br /> }<br /> // B now includes meth1() and meth2() -- it adds meth3().<br /> interface B extends A {<br /> void meth3();<br /> }<br /> // This class must implement all of A and B<br /> class MyClass implements B {<br /> public void meth1() {<br /> System.out.println("Implement meth1().");<br /> }<br /> public void meth2() {<br /> System.out.println("Implement meth2().");<br /> }<br /> public void meth3() {<br /> System.out.println("Implement meth3().");<br /> }<br /> }<br /> class IFExtend {<br /> public static void main(String arg[]) {<br /> MyClass ob = new MyClass();</div> <div>THE JAVA LIBRARY<br /> Chapter 17: Input/Output: Exploring java.io 567<br /> tmp.getChars(0, length, c, 0);<br /> CharArrayReader input1 = new CharArrayReader(c);<br /> CharArrayReader input2 = new CharArrayReader(c, 0, 5);<br /> int i;<br /> System.out.println("input1 is:");<br /> while((i = input1.read()) != -1) {<br /> System.out.print((char)i);<br /> }<br /> System.out.println();<br /> }<br /> }<br /> System.out.println("input2 is:");<br /> while((i = input2.read()) != -1) {<br /> System.out.print((char)i);<br /> }<br /> System.out.println();<br /> The input1 object is constructed using the entire lowercase alphabet, while input2<br /> contains only the first five letters. Here is the output:<br /> input1 is:<br /> abcdefghijklmnopqrstuvwxyz<br /> input2 is:<br /> abcde<br /> CharArrayWriter<br /> CharArrayWriter is an implementation of an output stream that uses an array as the<br /> destination. CharArrayWriter has two constructors, shown here:<br /> CharArrayWriter( )<br /> CharArrayWriter(int numChars)<br /> In the first form, a buffer with a default size is created. In the second, a buffer is created<br /> with a size equal to that specified by numChars. The buffer is held in the buf field of<br /> CharArrayWriter. The buffer size will be increased automatically, if needed. The</div> <div>viii Java™ 2: The Complete Reference<br /> Robust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13<br /> Multithreaded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14<br /> Architecture-Neutral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14<br /> Interpreted and High Performance . . . . . . . . . . . . . . . . . . . . . . . . . 14<br /> Distributed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15<br /> Dynamic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15<br /> The Continuing Revolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15<br /> 2 An Overview of Java . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17<br /> Object-Oriented Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18<br /> Two Paradigms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18<br /> Abstraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18<br /> The Three OOP Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19<br /> A First Simple Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25<br /> Entering the Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25<br /> Compiling the Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26<br /> A Closer Look at the First Sample Program . . . . . . . . . . . . . . . . . . 27<br /> A Second Short Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29<br /> Two Control Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31<br /> The if Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31<br /> The for Loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33<br /> Using Blocks of Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35<br /> Lexical Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37<br /> Whitespace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37<br /> Identifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37<br /> Literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37<br /> Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38<br /> Separators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38<br /> The Java Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38<br /> The Java Class Libraries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39<br /> 3 Data Types, Variables, and Arrays . . . . . . . . . . . . . . . . . . . . . . 41<br /> Java Is a Strongly Typed Language . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42<br /> The Simple Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42<br /> Integers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43<br /> byte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44<br /> short . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44<br /> int . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44<br /> long . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45<br /> Floating-Point Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45<br /> float . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46<br /> double . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46<br /> Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47<br /> Booleans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48<br /> A Closer Look at Literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50<br /> Integer Literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50<br /> Floating-Point Literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50<br /> Boolean Literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 25: Java Beans 919<br /> Figure 25-13.<br /> The third page of the Interaction Wizard.<br /> Next, repeat this process, except this time, wire the connection from the scroll bar<br /> to the slider box.<br /> Finally, test the application. To do this, uncheck the Design Mode check box. This<br /> causes the application to execute, as shown in Figure 25-14. Try moving the slider<br /> box. When it moves, the scroll bar automatically moves, too. This is because of the<br /> connection that we wired from the slider to the scroll bar. Assuming that you also<br /> wired the reverse connection, moving the scroll bar will cause the slider to move.</div> <div>928 Java™ 2: The Complete Reference<br /> name of that country is displayed in the text field. The applet begins by getting its<br /> content pane and setting the layout manager of that pane. Four image buttons are<br /> created and added to the content pane. Next, the applet is registered to receive action<br /> events that are generated by the buttons. A text field is then created and added to the<br /> applet. Finally, a handler for action events displays the command string that is<br /> associated with the button. The text field is used to present this string.<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import javax.swing.*;<br /> /*<br /> <applet code="JButtonDemo" width=250 height=300><br /> </applet><br /> */<br /> public class JButtonDemo extends JApplet<br /> implements ActionListener {<br /> JTextField jtf;<br /> public void init() {<br /> // Get content pane<br /> Container contentPane = getContentPane();<br /> contentPane.setLayout(new FlowLayout());<br /> // Add buttons to content pane<br /> ImageIcon france = new ImageIcon("france.gif");<br /> JButton jb = new JButton(france);<br /> jb.setActionCommand("France");<br /> jb.addActionListener(this);<br /> contentPane.add(jb);<br /> ImageIcon germany = new ImageIcon("germany.gif");<br /> jb = new JButton(germany);<br /> jb.setActionCommand("Germany");<br /> jb.addActionListener(this);<br /> contentPane.add(jb);<br /> ImageIcon italy = new ImageIcon("italy.gif");<br /> jb = new JButton(italy);<br /> jb.setActionCommand("Italy");</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 25: Java Beans 905<br /> Figure 25-5.<br /> Using the ColorsBeanInfo Class<br /> Constrained Properties<br /> A Bean that has a constrained property generates an event when an attempt is made to<br /> change its value. The event is of type PropertyChangeEvent. It is sent to objects that<br /> previously registered an interest in receiving such notifications. Those other objects<br /> have the ability to veto the proposed change. This capability allows a Bean to operate<br /> differently according to its run-time environment. A full discussion of constrained<br /> properties is beyond the scope of this book.<br /> Persistence<br /> Persistence is the ability to save a Bean to nonvolatile storage and retrieve it at a later<br /> time. The information that is particularly important are the configuration settings.</div> <div>THE JAVA LANGUAGE<br /> Chapter 7: A Closer Look at Methods and Classes 161<br /> }<br /> // constructor used when all dimensions specified<br /> Box(double w, double h, double d) {<br /> width = w;<br /> height = h;<br /> depth = d;<br /> }<br /> // constructor used when no dimensions specified<br /> Box() {<br /> width = -1; // use -1 to indicate<br /> height = -1; // an uninitialized<br /> depth = -1; // box<br /> }<br /> // constructor used when cube is created<br /> Box(double len) {<br /> width = height = depth = len;<br /> }<br /> // compute and return volume<br /> double volume() {<br /> return width * height * depth;<br /> }<br /> class OverloadCons {<br /> public static void main(String args[]) {<br /> // create boxes using the various constructors<br /> Box mybox1 = new Box(10, 20, 15);<br /> Box mybox2 = new Box();<br /> Box mycube = new Box(7);<br /> double vol;<br /> // get volume of first box<br /> vol = mybox1.volume();<br /> System.out.println("Volume of mybox1 is " + vol);<br /> // get volume of second box<br /> vol = mybox2.volume();<br /> System.out.println("Volume of mybox2 is " + vol);</div> <div>720 Java™ 2: The Complete Reference<br /> }<br /> g.drawString(msg, 4, 16);<br /> }<br /> Sample output from this program is shown next. However, when you run this<br /> program, you may see a different list of fonts than the one shown in this illustration.<br /> Prior to Java 2, you would use the method getFontList( ) defined by the Toolkit class<br /> to obtain a list of fonts. This method is now deprecated and should not be used by<br /> new programs.<br /> Creating and Selecting a Font<br /> To select a new font, you must first construct a Font object that describes that font.<br /> One Font constructor has this general form:<br /> Font(String fontName, int fontStyle, int pointSize)<br /> Here, fontName specifies the name of the desired font. The name can be specified using<br /> either the logical or face name. All Java environments will support the following fonts:<br /> Dialog, DialogInput, Sans Serif, Serif, Monospaced, and Symbol. Dialog is the font used<br /> by your system’s dialog boxes. Dialog is also the default if you don’t explicitly set a<br /> font. You can also use any other fonts supported by your particular environment, but<br /> be careful—these other fonts may not be universally available.<br /> The style of the font is specified by fontStyle. It may consist of one or more of these<br /> three constants: Font.PLAIN, Font.BOLD, and Font.ITALIC. To combine styles, OR<br /> them together. For example, Font.BOLD | Font.ITALIC specifies a bold, italics style.<br /> The size, in points, of the font is specified by pointSize.<br /> To use a font that you have created, you must select it using setFont( ), which is<br /> defined by Component. It has this general form:<br /> void setFont(Font fontObj)<br /> Here, fontObj is the object that contains the desired font.<br /> The following program outputs a sample of each standard font. Each time you click<br /> the mouse within its window, a new font is selected and its name is displayed.</div> <div>32 Java™ 2: The Complete Reference<br /> Here, condition is a Boolean expression. If condition is true, then the statement is<br /> executed. If condition is false, then the statement is bypassed. Here is an example:<br /> if(num < 100) println("num is less than 100");<br /> In this case, if num contains a value that is less than 100, the conditional expression<br /> is true, and println( ) will execute. If num contains a value greater than or equal to 100,<br /> then the println( ) method is bypassed.<br /> As you will see in Chapter 4, Java defines a full complement of relational operators<br /> which may be used in a conditional expression. Here are a few:<br /> Operator<br /> Meaning<br /> < Less than<br /> > Greater than<br /> == Equal to<br /> Notice that the test for equality is the double equal sign.<br /> Here is a program that illustrates the if statement:<br /> /*<br /> Demonstrate the if.<br /> Call this file "IfSample.java".<br /> */<br /> class IfSample {<br /> public static void main(String args[]) {<br /> int x, y;<br /> x = 10;<br /> y = 20;<br /> if(x < y) System.out.println("x is less than y");<br /> x = x * 2;<br /> if(x == y) System.out.println("x now equal to y");<br /> x = x * 2;<br /> if(x > y) System.out.println("x now greater than y");</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 26: A Tour of Swing 925<br /> <applet code="JLabelDemo" width=250 height=150><br /> </applet><br /> */<br /> public class JLabelDemo extends JApplet {<br /> public void init() {<br /> // Get content pane<br /> Container contentPane = getContentPane();<br /> // Create an icon<br /> ImageIcon ii = new ImageIcon("france.gif");<br /> // Create a label<br /> JLabel jl = new JLabel("France", ii, JLabel.CENTER);<br /> }<br /> }<br /> // Add label to the content pane<br /> contentPane.add(jl);<br /> Output from this applet is shown here:<br /> Text Fields<br /> The Swing text field is encapsulated by the JTextComponent class, which extends<br /> JComponent. It provides functionality that is common to Swing text components. One</div> <div>THE JAVA LANGUAGE<br /> Chapter 2: An Overview of Java 19<br /> A powerful way to manage abstraction is through the use of hierarchical classifications.<br /> This allows you to layer the semantics of complex systems, breaking them into more<br /> manageable pieces. From the outside, the car is a single object. Once inside, you see<br /> that the car consists of several subsystems: steering, brakes, sound system, seat belts,<br /> heating, cellular phone, and so on. In turn, each of these subsystems is made up of more<br /> specialized units. For instance, the sound system consists of a radio, a CD player, and/or<br /> a tape player. The point is that you manage the complexity of the car (or any other<br /> complex system) through the use of hierarchical abstractions.<br /> Hierarchical abstractions of complex systems can also be applied to computer<br /> programs. The data from a traditional process-oriented program can be transformed<br /> by abstraction into its component objects. A sequence of process steps can become a<br /> collection of messages between these objects. Thus, each of these objects describes its<br /> own unique behavior. You can treat these objects as concrete entities that respond to<br /> messages telling them to do something. This is the essence of object-oriented programming.<br /> Object-oriented concepts form the heart of Java just as they form the basis for human<br /> understanding. It is important that you understand how these concepts translate into<br /> programs. As you will see, object-oriented programming is a powerful and natural<br /> paradigm for creating programs that survive the inevitable changes accompanying the<br /> life cycle of any major software project, including conception, growth, and aging. For<br /> example, once you have well-defined objects and clean, reliable interfaces to those objects,<br /> you can gracefully decommission or replace parts of an older system without fear.<br /> The Three OOP Principles<br /> All object-oriented programming languages provide mechanisms that help you implement<br /> the object-oriented model. They are encapsulation, inheritance, and polymorphism.<br /> Let’s take a look at these concepts now.<br /> Encapsulation<br /> Encapsulation is the mechanism that binds together code and the data it manipulates,<br /> and keeps both safe from outside interference and misuse. One way to think about<br /> encapsulation is as a protective wrapper that prevents the code and data from being<br /> arbitrarily accessed by other code defined outside the wrapper. Access to the code<br /> and data inside the wrapper is tightly controlled through a well-defined interface.<br /> To relate this to the real world, consider the automatic transmission on an automobile.<br /> It encapsulates hundreds of bits of information about your engine, such as how much<br /> you are accelerating, the pitch of the surface you are on, and the position of the shift<br /> lever. You, as the user, have only one method of affecting this complex encapsulation:<br /> by moving the gear-shift lever. You can’t affect the transmission by using the turn signal<br /> or windshield wipers, for example. Thus, the gear-shift lever is a well-defined (indeed,<br /> unique) interface to the transmission. Further, what occurs inside the transmission does<br /> not affect objects outside the transmission. For example, shifting gears does not turn<br /> on the headlights! Because an automatic transmission is encapsulated, dozens of car</div> <div>180 Java™ 2: The Complete Reference<br /> You can put the length member to good use in many situations. For example, here<br /> is an improved version of the Stack class. As you might recall, the earlier versions of<br /> this class always created a ten-element stack. The following version lets you create<br /> stacks of any size. The value of stck.length is used to prevent the stack from<br /> overflowing.<br /> // Improved Stack class that uses the length array member.<br /> class Stack {<br /> private int stck[];<br /> private int tos;<br /> }<br /> // allocate and initialize stack<br /> Stack(int size) {<br /> stck = new int[size];<br /> tos = -1;<br /> }<br /> // Push an item onto the stack<br /> void push(int item) {<br /> if(tos==stck.length-1) // use length member<br /> System.out.println("Stack is full.");<br /> else<br /> stck[++tos] = item;<br /> }<br /> // Pop an item from the stack<br /> int pop() {<br /> if(tos < 0) {<br /> System.out.println("Stack underflow.");<br /> return 0;<br /> }<br /> else<br /> return stck[tos--];<br /> }<br /> class TestStack2 {<br /> public static void main(String args[]) {<br /> Stack mystack1 = new Stack(5);<br /> Stack mystack2 = new Stack(8);</div> <div>THE JAVA LANGUAGE<br /> Chapter 7: A Closer Look at Methods and Classes 187<br /> if(strOb1.equals(strOb2))<br /> System.out.println("strOb1 == strOb2");<br /> else<br /> System.out.println("strOb1 != strOb2");<br /> }<br /> }<br /> if(strOb1.equals(strOb3))<br /> System.out.println("strOb1 == strOb3");<br /> else<br /> System.out.println("strOb1 != strOb3");<br /> This program generates the following output:<br /> Length of strOb1: 12<br /> Char at index 3 in strOb1: s<br /> strOb1 != strOb2<br /> strOb1 == strOb3<br /> Of course, you can have arrays of strings, just like you can have arrays of any other<br /> type of object. For example:<br /> // Demonstrate String arrays.<br /> class StringDemo3 {<br /> public static void main(String args[]) {<br /> String str[] = { "one", "two", "three" };<br /> }<br /> }<br /> for(int i=0; i<str.length; i++)<br /> System.out.println("str[" + i + "]: " +<br /> str[i]);<br /> Here is the output from this program:<br /> str[0]: one<br /> str[1]: two<br /> str[2]: three<br /> As you will see in the following section, string arrays play an important part in<br /> many Java programs.</div> <div>582 Java™ 2: The Complete Reference<br /> Method<br /> int read( )<br /> int read(byte buffer[ ], int offset,<br /> int numBytes)<br /> boolean readBoolean( )<br /> byte readByte( )<br /> char readChar( )<br /> double readDouble( )<br /> float readFloat( )<br /> void readFully(byte buffer[ ])<br /> void readFully(byte buffer[ ],<br /> int offset,<br /> int numBytes)<br /> int readInt( )<br /> long readLong( )<br /> final Object readObject( )<br /> Description<br /> Returns an integer representation of the next<br /> available byte of input. –1 is returned when<br /> the end of the file is encountered.<br /> Attempts to read up to numBytes bytes into<br /> buffer starting at buffer[offset], returning the<br /> number of bytes successfully read. –1 is<br /> returned when the end of the file is<br /> encountered.<br /> Reads and returns a boolean from the<br /> invoking stream.<br /> Reads and returns a byte from the<br /> invoking stream.<br /> Reads and returns a char from the<br /> invoking stream.<br /> Reads and returns a double from the<br /> invoking stream.<br /> Reads and returns a float from the<br /> invoking stream.<br /> Reads buffer.length bytes into buffer. Returns<br /> only when all bytes have been read.<br /> Reads numBytes bytes into buffer starting at<br /> buffer[offset]. Returns only when numBytes<br /> have been read.<br /> Reads and returns an int from the<br /> invoking stream.<br /> Reads and returns a long from the<br /> invoking stream.<br /> Reads and returns an object from the<br /> invoking stream.<br /> Table 17-8.<br /> Commonly Used Methods Defined by ObjectInputStream (continued)</div> <div>280 Java™ 2: The Complete Reference<br /> Creating a Thread<br /> In the most general sense, you create a thread by instantiating an object of type Thread.<br /> Java defines two ways in which this can be accomplished:<br /> ■ You can implement the Runnable interface.<br /> ■ You can extend the Thread class, itself.<br /> The following two sections look at each method, in turn.<br /> Implementing Runnable<br /> The easiest way to create a thread is to create a class that implements the Runnable<br /> interface. Runnable abstracts a unit of executable code. You can construct a thread on<br /> any object that implements Runnable. To implement Runnable, a class need only<br /> implement a single method called run( ), which is declared like this:<br /> public void run( )<br /> Inside run( ), you will define the code that constitutes the new thread. It is<br /> important to understand that run( ) can call other methods, use other classes, and<br /> declare variables, just like the main thread can. The only difference is that run( )<br /> establishes the entry point for another, concurrent thread of execution within your<br /> program. This thread will end when run( ) returns.<br /> After you create a class that implements Runnable, you will instantiate an object of<br /> type Thread from within that class. Thread defines several constructors. The one that<br /> we will use is shown here:<br /> Thread(Runnable threadOb, String threadName)<br /> In this constructor, threadOb is an instance of a class that implements the Runnable<br /> interface. This defines where execution of the thread will begin. The name of the new<br /> thread is specified by threadName.<br /> After the new thread is created, it will not start running until you call its start( )<br /> method, which is declared within Thread. In essence, start( ) executes a call to run( ).<br /> The start( ) method is shown here:<br /> void start( )<br /> Here is an example that creates a new thread and starts it running:</div> <div>578 Java™ 2: The Complete Reference<br /> Externalizable<br /> The Java facilities for serialization and deserialization have been designed so that much<br /> of the work to save and restore the state of an object occurs automatically. However,<br /> there are cases in which the programmer may need to have control over these<br /> processes. For example, it may be desirable to use compression or encryption<br /> techniques. The Externalizable interface is designed for these situations.<br /> The Externalizable interface defines these two methods:<br /> void readExternal(ObjectInput inStream)<br /> throws IOException, ClassNotFoundException<br /> void writeExternal(ObjectOutput outStream)<br /> throws IOException<br /> In these methods, inStream is the byte stream from which the object is to be read, and<br /> outStream is the byte stream to which the object is to be written.<br /> ObjectOutput<br /> The ObjectOutput interface extends the DataOutput interface and supports object<br /> serialization. It defines the methods shown in Table 17-5. Note especially the<br /> writeObject( ) method. This is called to serialize an object. All of these methods will<br /> throw an IOException on error conditions.<br /> Method<br /> void close( )<br /> void flush( )<br /> void write(byte buffer[ ])<br /> void write(byte buffer[ ], int offset,<br /> int numBytes)<br /> void write(int b)<br /> void writeObject(Object obj)<br /> Description<br /> Closes the invoking stream. Further write<br /> attempts will generate an IOException.<br /> Finalizes the output state so that any<br /> buffers are cleared. That is, it flushes the<br /> output buffers.<br /> Writes an array of bytes to the invoking<br /> stream.<br /> Writes a subrange of numBytes bytes from<br /> the array buffer, beginning at buffer[offset].<br /> Writes a single byte to the invoking stream.<br /> The byte written is the low-order byte of b.<br /> Writes object obj to the invoking stream.<br /> Table 17-5.<br /> The Methods Defined by ObjectOutput</div> <div>THE JAVA LANGUAGE<br /> Chapter 6: Introducing Classes 149<br /> Box mybox1 = new Box(10, 20, 15);<br /> the values 10, 20, and 15 are passed to the Box( ) constructor when new creates the<br /> object. Thus, mybox1’s copy of width, height, and depth will contain the values 10,<br /> 20, and 15, respectively.<br /> The this Keyword<br /> Sometimes a method will need to refer to the object that invoked it. To allow this, Java<br /> defines the this keyword. this can be used inside any method to refer to the current object.<br /> That is, this is always a reference to the object on which the method was invoked. You<br /> can use this anywhere a reference to an object of the current class’ type is permitted.<br /> To better understand what this refers to, consider the following version of Box( ):<br /> // A redundant use of this.<br /> Box(double w, double h, double d) {<br /> this.width = w;<br /> this.height = h;<br /> this.depth = d;<br /> }<br /> This version of Box( ) operates exactly like the earlier version. The use of this is redundant,<br /> but perfectly correct. Inside Box( ), this will always refer to the invoking object. While<br /> it is redundant in this case, this is useful in other contexts, one of which is explained in<br /> the next section.<br /> Instance Variable Hiding<br /> As you know, it is illegal in Java to declare two local variables with the same name<br /> inside the same or enclosing scopes. Interestingly, you can have local variables,<br /> including formal parameters to methods, which overlap with the names of the class’<br /> instance variables. However, when a local variable has the same name as an instance<br /> variable, the local variable hides the instance variable. This is why width, height, and<br /> depth were not used as the names of the parameters to the Box( ) constructor inside the<br /> Box class. If they had been, then width would have referred to the formal parameter,<br /> hiding the instance variable width. While it is usually easier to simply use different<br /> names, there is another way around this situation. Because this lets you refer directly<br /> to the object, you can use it to resolve any name space collisions that might occur<br /> between instance variables and local variables. For example, here is another version of</div> <div>APPLYING JAVA<br /> Chapter 32: Scrabblet: A Multiplayer Word Game 1121<br /> }<br /> for (int i = 0; i < keystrings.length; i++)<br /> keys.put(keystrings[i], new Integer(i));<br /> private int lookup(String s) {<br /> Integer i = (Integer) keys.get(s);<br /> return i == null ? -1 : i.intValue();<br /> }<br /> run( )<br /> run( ) is the main loop of the game’s connection to the server. It goes into a blocking<br /> call to readline( ) that will return with a String whenever a line of text comes from the<br /> server. It uses a StringTokenizer to break the line into words. The switch statement<br /> dispatches us to the right code, based on the first word in the input line. Each of the<br /> keywords in the protocol parses the input line differently, and most of them make<br /> method calls back into the Scrabblet class to do their work.<br /> public void run() {<br /> String s;<br /> StringTokenizer st;<br /> while ((s = readline()) != null) {<br /> st = new StringTokenizer(s);<br /> String keyword = st.nextToken();<br /> switch (lookup(keyword)) {<br /> default:<br /> System.out.println("bogus keyword: " + keyword + "\r");<br /> break;<br /> case ID:<br /> id = st.nextToken();<br /> break;<br /> case ADD: {<br /> String id = st.nextToken();<br /> String hostname = st.nextToken();<br /> String name = st.nextToken(CRLF);<br /> scrabblet.add(id, hostname, name);<br /> }<br /> break;<br /> case DELETE:</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 28: Migrating from C++ to Java 997<br /> In this program, the abstract class IntList defines only the form of an integer list. It<br /> contains only pure virtual functions and does not declare any data. For these reasons, it<br /> can be made into an interface when the program is converted into Java, as shown here:<br /> // Here, IntList is made into an interface which IntArray implements.<br /> // Define interface for an integer list.<br /> interface IntListIF {<br /> int getNext();<br /> void putOnList(int i);<br /> }<br /> // Create an implementation of an integer list.<br /> class IntArray implements IntListIF {<br /> private int storage[];<br /> private int putIndex, getIndex;<br /> IntArray() {<br /> storage = new int[100];<br /> putIndex = 0;<br /> getIndex = 0;<br /> }<br /> // Create an implementation of an integer list.<br /> public int getNext() {<br /> if(getIndex >= 100) {<br /> System.out.println("List Underflow");<br /> System.exit(1);<br /> }<br /> getIndex++;<br /> return storage[getIndex-1];<br /> }<br /> // Put an integer on the list.<br /> public void putOnList(int i) {<br /> if(putIndex < 100) {<br /> storage[putIndex] = i;<br /> putIndex++;<br /> }<br /> else {<br /> System.out.println("List Overflow");</div> <div>166 Java™ 2: The Complete Reference<br /> class CallByValue {<br /> public static void main(String args[]) {<br /> Test ob = new Test();<br /> int a = 15, b = 20;<br /> System.out.println("a and b before call: " +<br /> a + " " + b);<br /> ob.meth(a, b);<br /> }<br /> }<br /> System.out.println("a and b after call: " +<br /> a + " " + b);<br /> The output from this program is shown here:<br /> a and b before call: 15 20<br /> a and b after call: 15 20<br /> As you can see, the operations that occur inside meth( ) have no effect on the values<br /> of a and b used in the call; their values here did not change to 30 and 10.<br /> When you pass an object to a method, the situation changes dramatically, because<br /> objects are passed by reference. Keep in mind that when you create a variable of a class<br /> type, you are only creating a reference to an object. Thus, when you pass this reference<br /> to a method, the parameter that receives it will refer to the same object as that referred<br /> to by the argument. This effectively means that objects are passed to methods by use of<br /> call-by-reference. Changes to the object inside the method do affect the object used as<br /> an argument. For example, consider the following program:<br /> // Objects are passed by reference.<br /> class Test {<br /> int a, b;<br /> Test(int i, int j) {<br /> a = i;<br /> b = j;<br /> }</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 25: Java Beans 889<br /> a directory called bdk. Ifthis is not the case with your system, substitute the proper<br /> directory.<br /> Starting the BDK<br /> To start the BDK, follow these steps:<br /> 1. Change to the directory c:\bdk\beanbox.<br /> 2. Execute the batch file called run.bat. This causes the BDK to display the three<br /> windows shown in Figure 25-1. ToolBox lists all of the different Beans that have<br /> been included with the BDK. BeanBox provides an area to lay out and connect<br /> the Beans selected from the ToolBox. Properties provides the ability to configure<br /> a selected Bean. You may also see a window called Method Tracer, but we<br /> won’t be using it.<br /> Using the BDK<br /> This section describes how to create an application by using some of the Beans<br /> provided with the BDK. First, the Molecule Bean displays a three-dimensional view of<br /> a molecule. It may be configured to present one of the following molecules: hyaluronic<br /> acid, benzene, buckminsterfullerine, cyclohexane, ethane, or water. This component<br /> also has methods that allow the molecule to be rotated in space along its X or Y axis.<br /> Figure 25-1.<br /> The Bean Developer Kit (BDK)</div> <div>THE JAVA LANGUAGE<br /> Chapter 2: An Overview of Java 33<br /> }<br /> }<br /> // this won't display anything<br /> if(x == y) System.out.println("you won't see this");<br /> The output generated by this program is shown here:<br /> x is less than y<br /> x now equal to y<br /> x now greater than y<br /> Notice one other thing in this program. The line<br /> int x, y;<br /> declares two variables, x and y, by use of a comma-separated list.<br /> The for Loop<br /> As you may know from your previous programming experience, loop statements are<br /> an important part of nearly any programming language. Java is no exception. In fact,<br /> as you will see in Chapter 5, Java supplies a powerful assortment of loop constructs.<br /> Perhaps the most versatile is the for loop. If you are familiar with C, C++, or C#, then<br /> you will be pleased to know that the for loop in Java works the same way it does in<br /> those languages. If you don’t know C/C++/C#, the for loop is still easy to use. The<br /> simplest form of the for loop is shown here:<br /> for(initialization; condition; iteration) statement;<br /> In its most common form, the initialization portion of the loop sets a loop control<br /> variable to an initial value. The condition is a Boolean expression that tests the loop<br /> control variable. If the outcome of that test is true, the for loop continues to iterate. If it<br /> is false, the loop terminates. The iteration expression determines how the loop control<br /> variable is changed each time the loop iterates. Here is a short program that illustrates<br /> the for loop:<br /> /*<br /> Demonstrate the for loop.<br /> Call this file "ForTest.java".</div> <div>THE JAVA LANGUAGE<br /> Chapter 5: Control Statements 107<br /> As you can see, execution falls through each case until a break statement (or the end of<br /> the switch) is reached.<br /> While the preceding example is, of course, contrived for the sake of illustration,<br /> omitting the break statement has many practical applications in real programs. To<br /> sample its more realistic usage, consider the following rewrite of the season example<br /> shown earlier. This version uses a switch to provide a more efficient implementation.<br /> // An improved version of the season program.<br /> class Switch {<br /> public static void main(String args[]) {<br /> int month = 4;<br /> String season;<br /> switch (month) {<br /> case 12:<br /> case 1:<br /> case 2:<br /> season = "Winter";<br /> break;<br /> case 3:<br /> case 4:<br /> case 5:<br /> season = "Spring";<br /> break;<br /> case 6:<br /> case 7:<br /> case 8:<br /> season = "Summer";<br /> break;<br /> case 9:<br /> case 10:<br /> case 11:<br /> season = "Autumn";<br /> break;<br /> default:<br /> season = "Bogus Month";<br /> }<br /> System.out.println("April is in the " + season + ".");<br /> }<br /> }</div> <div>1134 Java™ 2: The Complete Reference<br /> As explained in Part I, Java supports three types of comments. The first two are<br /> the // and the /* */. The third type is called a documentation comment. It begins<br /> with the character sequence /**. It ends with */. Documentation comments allow<br /> you to embed information about your program into the program itself. You can then<br /> use the javadoc utility program to extract the information and put it into an HTML file.<br /> Documentation comments make it convenient to document your programs. You have<br /> almost certainly seen documentation generated with javadoc, because that is the way<br /> the Java API library was documented by Sun.<br /> The javadoc Tags<br /> The javadoc utility recognizes the following tags:<br /> Tag<br /> @author<br /> @deprecated<br /> {@docRoot}<br /> @exception<br /> {@inheritDoc}<br /> {@link}<br /> {@linkplain}<br /> @param<br /> @return<br /> @see<br /> @serial<br /> Meaning<br /> Identifies the author of a class.<br /> Specifies that a class or member is deprecated.<br /> Specifies the path to the root directory of the current<br /> documentation (added by Java 2, version 1.3).<br /> Identifies an exception thrown by a method.<br /> Inherits a comment from the immediate superclass. (Added by<br /> Java 2, version 1.4, but not currently implemented.)<br /> Inserts an in-line link to another topic.<br /> Inserts an in-line link to another topic, but the link is displayed<br /> in a plain-text font. (Added by Java 2, version 1.4.)<br /> Documents a method’s parameter.<br /> Documents a method’s return value.<br /> Specifies a link to another topic.<br /> Documents a default serializable field.<br /> @serialData Documents the data written by the writeObject( )<br /> or writeExternal( ) methods.<br /> @serialField Documents an ObjectStreamField component.<br /> @since<br /> States the release when a specific change was introduced.<br /> @throws Same as @exception.<br /> {@value} Displays the value of a constant, which must be a static field.<br /> (Added by Java 2, version 1.4.)<br /> @version Specifies the version of a class.</div> <div>THE JAVA LANGUAGE<br /> Chapter 3: Data Types, Variables, and Arrays 61<br /> double result = (f * b) + (i / c) - (d * s);<br /> In the first subexpression, f*b, b is promoted to a float and the result of the subexpression<br /> is float. Next, in the subexpression i / c, c is promoted to int, and the result is of type<br /> int. Then, in d*s, the value of s is promoted to double, and the type of the subexpression<br /> is double. Finally, these three intermediate values, float, int, and double, are considered.<br /> The outcome of float plus an int is a float. Then the resultant float minus the last<br /> double is promoted to double, which is the type for the final result of the expression.<br /> Arrays<br /> An array is a group of like-typed variables that are referred to by a common name. Arrays<br /> of any type can be created and may have one or more dimensions. A specific element<br /> in an array is accessed by its index. Arrays offer a convenient means of grouping<br /> related information.<br /> If you are familiar with C/C++, be careful. Arrays in Java work differently than they do<br /> in those languages.<br /> One-Dimensional Arrays<br /> A one-dimensional array is, essentially, a list of like-typed variables. To create an array,<br /> you first must create an array variable of the desired type. The general form of a onedimensional<br /> array declaration is<br /> type var-name[ ];<br /> Here, type declares the base type of the array. The base type determines the data type<br /> of each element that comprises the array. Thus, the base type for the array determines<br /> what type of data the array will hold. For example, the following declares an array<br /> named month_days with the type “array of int”:<br /> int month_days[];<br /> Although this declaration establishes the fact that month_days is an array variable,<br /> no array actually exists. In fact, the value of month_days is set to null, which represents<br /> an array with no value. To link month_days with an actual, physical array of integers,</div> <div>THE JAVA LIBRARY<br /> Chapter 20: Event Handling 665<br /> when. The modifiers argument indicates which modifiers were pressed when a mouse<br /> event occurred. The coordinates of the mouse are passed in x and y. The click count is<br /> passed in clicks. The triggersPopup flag indicates if this event causes a pop-up menu to<br /> appear on this platform. Java 2, version 1.4 adds a second constructor which also allows<br /> the button that caused the event to be specified.<br /> The most commonly used methods in this class are getX( ) and getY( ). These<br /> return the X and Y coordinates of the mouse when the event occurred. Their forms<br /> are shown here:<br /> int getX( )<br /> int getY( )<br /> Alternatively, you can use the getPoint( ) method to obtain the coordinates of the<br /> mouse. It is shown here:<br /> Point getPoint( )<br /> It returns a Point object that contains the X, Y coordinates in its integer members: x and y.<br /> The translatePoint( ) method changes the location of the event. Its form is shown here:<br /> void translatePoint(int x, int y)<br /> Here, the arguments x and y are added to the coordinates of the event.<br /> The getClickCount( ) method obtains the number of mouse clicks for this event.<br /> Its signature is shown here:<br /> int getClickCount( )<br /> The isPopupTrigger( ) method tests if this event causes a pop-up menu to appear<br /> on this platform. Its form is shown here:<br /> boolean isPopupTrigger( )<br /> Java 2, version 1.4 added the getButton( ) method, shown here.<br /> int getButton( )<br /> It returns a value that represents the button that caused the event. The return value<br /> will be one of these constants defined by MouseEvent.<br /> NOBUTTON BUTTON1 BUTTON2 BUTTON3<br /> The NOBUTTON value indicates that no button was pressed or released.<br /> The MouseWheelEvent Class<br /> The MouseWheelEvent class encapsulates a mouse wheel event. It is a subclass<br /> of MouseEvent and was added by Java 2, version 1.4. Not all mice have wheels.</div> <div>About the Author<br /> Herbert Schildt is the world’s leading<br /> programming author. He is an authority on the<br /> C, C++, Java, and C# languages, and is a master<br /> Windows programmer. His programming books<br /> have sold more that 3 million copies worldwide<br /> and have been translated into all major foreign<br /> languages. He is the author of numerous<br /> bestsellers, including Java 2: The Complete<br /> Reference, Java 2: A Beginner's Guide, Java 2<br /> Programmers Reference, C++: The Complete<br /> Reference, C: The Complete Reference, and C#:<br /> The Complete Reference. Schildt holds a master's<br /> degree in computer science from the University<br /> of Illinois. He can be reached at his consulting<br /> office at (217) 586-4683.</div> <div>THE JAVA LIBRARY<br /> Chapter 15: java.util Part 1: The Collections Framework 477<br /> Method<br /> static Object min(Collection c,<br /> Comparator comp)<br /> static Object min(Collection c)<br /> static List nCopies(int num, Object obj)<br /> static boolean replaceAll(List list,<br /> Object old,<br /> Object new)<br /> static void reverse(List list)<br /> static Comparator reverseOrder( )<br /> static void rotate(List list, int n)<br /> static void shuffle(List list, Random r)<br /> static void shuffle(List list)<br /> static Set singleton(Object obj)<br /> Description<br /> Returns the minimum element<br /> in c as determined by comp. The<br /> collection need not be sorted.<br /> Returns the minimum element<br /> in c as determined by natural<br /> ordering.<br /> Returns num copies of obj<br /> contained in an immutable list.<br /> num must be greater than or<br /> equal to zero.<br /> Replaces all occurrences of old<br /> with new in list. Returns true if at<br /> least one replacement occurred.<br /> Returns false, otherwise. (Added<br /> by Java 2, v1.4)<br /> Reverses the sequence in list.<br /> Returns a reverse comparator<br /> (a comparator that reverses the<br /> outcome of a comparison<br /> between two elements).<br /> Rotates list by n places to<br /> the right. To rotate left, use a<br /> negative value for n. (Added<br /> by Java 2, v1.4)<br /> Shuffles (i.e., randomizes) the<br /> elements in list by using r as a<br /> source of random numbers.<br /> Shuffles (i.e., randomizes) the<br /> elements in list.<br /> Returns obj as an immutable set.<br /> This is an easy way to convert a<br /> single object into a set.<br /> Table 15-9.<br /> The Algorithms Defined by Collections (continued)</div> <div>This page intentionally left blank.</div> <div>THE JAVA LIBRARY<br /> Chapter 17: Input/Output: Exploring java.io 583<br /> Method<br /> short readShort( )<br /> int readUnsignedByte( )<br /> int readUnsignedShort( )<br /> Description<br /> Reads and returns a short from the invoking<br /> stream.<br /> Reads and returns an unsigned byte from the<br /> invoking stream.<br /> Reads an unsigned short from the invoking<br /> stream.<br /> Table 17-8.<br /> Commonly Used Methods Defined by ObjectInputStream (continued)<br /> A Serialization Example<br /> The following program illustrates how to use object serialization and deserialization.<br /> It begins by instantiating an object of class MyClass. This object has three instance<br /> variables that are of types String, int, and double. This is the information we want to<br /> save and restore.<br /> A FileOutputStream is created that refers to a file named “serial,” and an<br /> ObjectOutputStream is created for that file stream. The writeObject( ) method<br /> of ObjectOutputStream is then used to serialize our object. The object output<br /> stream is flushed and closed.<br /> A FileInputStream is then created that refers to the file named “serial,” and<br /> an ObjectInputStream is created for that file stream. The readObject( ) method of<br /> ObjectInputStream is then used to deserialize our object. The object input stream is<br /> then closed.<br /> Note that MyClass is defined to implement the Serializable interface. If this is not<br /> done, a NotSerializableException is thrown. Try experimenting with this program by<br /> declaring some of the MyClass instance variables to be transient. That data is then not<br /> saved during serialization.<br /> import java.io.*;<br /> public class SerializationDemo {<br /> public static void main(String args[]) {<br /> // Object serialization<br /> try {</div> <div>660 Java™ 2: The Complete Reference<br /> The amount of the adjustment can be obtained from the getValue( ) method, shown here:<br /> int getValue( )<br /> For example, when a scroll bar is manipulated, this method returns the value represented<br /> by that change.<br /> The ComponentEvent Class<br /> A ComponentEvent is generated when the size, position, or visibility of a component<br /> is changed. There are four types of component events. The ComponentEvent class<br /> defines integer constants that can be used to identify them. The constants and their<br /> meanings are shown here:<br /> COMPONENT_HIDDEN<br /> COMPONENT_MOVED<br /> COMPONENT_RESIZED<br /> COMPONENT_SHOWN<br /> The component was hidden.<br /> The component was moved.<br /> The component was resized.<br /> The component became visible.<br /> ComponentEvent has this constructor:<br /> ComponentEvent(Component src, int type)<br /> Here, src is a reference to the object that generated this event. The type of the event is<br /> specified by type.<br /> ComponentEvent is the superclass either directly or indirectly of ContainerEvent,<br /> FocusEvent, KeyEvent, MouseEvent, and WindowEvent.<br /> The getComponent( ) method returns the component that generated the event. It is<br /> shown here:<br /> Component getComponent( )<br /> The ContainerEvent Class<br /> A ContainerEvent is generated when a component is added to or removed from a<br /> container. There are two types of container events. The ContainerEvent class defines<br /> int constants that can be used to identify them: COMPONENT_ADDED and<br /> COMPONENT_REMOVED. They indicate that a component has been added<br /> to or removed from the container.<br /> ContainerEvent is a subclass of ComponentEvent and has this constructor:<br /> ContainerEvent(Component src, int type, Component comp)<br /> Here, src is a reference to the container that generated this event. The type of the event<br /> is specified by type, and the component that has been added to or removed from the<br /> container is comp.</div> <div>Contents at a Glance<br /> Part I<br /> The Java Language<br /> 1 The Genesis of Java . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3<br /> 2 An Overview of Java . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17<br /> 3 Data Types, Variables, and Arrays . . . . . . . . . . . . . . . . . . . . . . . 41<br /> 4 Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73<br /> 5 Control Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99<br /> 6 Introducing Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129<br /> 7 A Closer Look at Methods and Classes . . . . . . . . . . . . . . . . . . . 155<br /> 8 Inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189<br /> 9 Packages and Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223<br /> 10 Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249<br /> 11 Multithreaded Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . 273<br /> 12 I/O, Applets, and Other Topics . . . . . . . . . . . . . . . . . . . . . . . . . 313<br /> v</div> <div>1016 Java™ 2: The Complete Reference<br /> In start( ), the mouse cursor is changed to a hand so that when the mouse cursor is<br /> over the applet, it will appear to be a link.<br /> run( )<br /> The run( ) method starts with a loop that waits for the first image to be fully loaded<br /> before proceeding. It then finishes the initialization of the applet by calling<br /> finishInit( ). From there, it enters the main loop of the program.<br /> This main loop drives the transitions between billboards. Using the delay<br /> parameter passed in from the HTML to the applet, the applet calculates when the next<br /> transition is supposed to be run. While it is waiting, it prepares for the transition. It<br /> starts the preparation by determining which billboard is to be displayed next, parsing<br /> the billboard data from HTML parameters if this has not been done yet for this<br /> billboard. Then it randomly chooses which transition to run next, being careful not to<br /> let the applet run the same transition consecutively.<br /> Once the applet has determined what transition will be run next, it creates a new<br /> instance of this transition class by dynamically loading the class using the String name<br /> and then creating a new instance of the class. The dynamic loading of the transition<br /> classes has a big impact on the loading time of the applet as a whole. Instead of every<br /> single class having to be downloaded before the applet starts, only three classes are<br /> sent initially: DynamicBillboard, BillData, and BillTransition. The other transition<br /> classes are only downloaded by the applet the first time they are needed. This reduces<br /> the initial download of the applet significantly. Some class files might not even need to<br /> be sent if the user leaves the page quickly.<br /> Finally, the applet calls the init( ) method on the transition object, passing the<br /> applet and image pixels for the current and next billboard as parameters. This creates<br /> all the cell frames that are used to animate a transition. With the transition ready to go,<br /> the applet only need wait for the proper time to start the transition.<br /> The applet performs the transition by using simple frame animation—drawing each<br /> cell in order onto the screen, with a short delay between each frame. The applet calls<br /> the toolkit method sync( ) just to be sure that the drawing of one cell does not take<br /> place before the previous cell has been shown on the screen. After the last cell is<br /> displayed, the applet draws the image from the next billboard onto the screen to<br /> complete the transition.<br /> Following this, the mouse_over_applet flag is checked to see if the mouse cursor<br /> is currently over the applet. If so, the URL of the previous billboard is showing on the<br /> status bar and must be updated to reflect the URL of the new billboard. This is done<br /> with a call to the applet method showStatus( ). The applet has completed this<br /> transition and is now ready to begin the next one.<br /> mouseMoved( ) and mouseExited( )<br /> mouseMoved( ) and mouseExited( ) are used to change the text that appears on the<br /> status bar. When the mouse cursor is over the applet, the status bar is supposed to<br /> show the URL that the current billboard links to. So when mouseMoved( ) gets called,</div> <div>160 Java™ 2: The Complete Reference<br /> class Box {<br /> double width;<br /> double height;<br /> double depth;<br /> }<br /> // This is the constructor for Box.<br /> Box(double w, double h, double d) {<br /> width = w;<br /> height = h;<br /> depth = d;<br /> }<br /> // compute and return volume<br /> double volume() {<br /> return width * height * depth;<br /> }<br /> As you can see, the Box( ) constructor requires three parameters. This means that<br /> all declarations of Box objects must pass three arguments to the Box( ) constructor. For<br /> example, the following statement is currently invalid:<br /> Box ob = new Box();<br /> Since Box( ) requires three arguments, it’s an error to call it without them. This<br /> raises some important questions. What if you simply wanted a box and did not care (or<br /> know) what its initial dimensions were? Or, what if you want to be able to initialize a<br /> cube by specifying only one value that would be used for all three dimensions? As the<br /> Box class is currently written, these other options are not available to you.<br /> Fortunately, the solution to these problems is quite easy: simply overload the Box<br /> constructor so that it handles the situations just described. Here is a program that<br /> contains an improved version of Box that does just that:<br /> /* Here, Box defines three constructors to initialize<br /> the dimensions of a box various ways.<br /> */<br /> class Box {<br /> double width;<br /> double height;<br /> double depth;</div> <div>500 Java™ 2: The Complete Reference<br /> another instance of Properties to be used as the default properties for the new instance.<br /> In this case, if you call getProperty(“foo”) on a given Properties object, and “foo” does<br /> not exist, Java looks for “foo” in the default Properties object. This allows for arbitrary<br /> nesting of levels of default properties.<br /> The following example demonstrates Properties. It creates a property list in which<br /> the keys are the names of states and the values are the names of their capitals. Notice<br /> that the attempt to find the capital for Florida includes a default value.<br /> // Demonstrate a Property list.<br /> import java.util.*;<br /> class PropDemo {<br /> public static void main(String args[]) {<br /> Properties capitals = new Properties();<br /> Set states;<br /> String str;<br /> capitals.put("Illinois", "Springfield");<br /> capitals.put("Missouri", "Jefferson City");<br /> capitals.put("Washington", "Olympia");<br /> capitals.put("California", "Sacramento");<br /> capitals.put("Indiana", "Indianapolis");<br /> // Show all states and capitals in hashtable.<br /> states = capitals.keySet(); // get set-view of keys<br /> Iterator itr = states.iterator();<br /> while(itr.hasNext()) {<br /> str = (String) itr.next();<br /> System.out.println("The capital of " +<br /> str + " is " +<br /> capitals.getProperty(str)<br /> + ".");<br /> }<br /> System.out.println();<br /> }<br /> }<br /> // look for state not in list -- specify default<br /> str = capitals.getProperty("Florida", "Not Found");<br /> System.out.println("The capital of Florida is "<br /> + str + ".");</div> <div>THE JAVA LANGUAGE<br /> Chapter 6: Introducing Classes 141<br /> // Now, volume() returns the volume of a box.<br /> class Box {<br /> double width;<br /> double height;<br /> double depth;<br /> }<br /> // compute and return volume<br /> double volume() {<br /> return width * height * depth;<br /> }<br /> class BoxDemo4 {<br /> public static void main(String args[]) {<br /> Box mybox1 = new Box();<br /> Box mybox2 = new Box();<br /> double vol;<br /> }<br /> }<br /> // assign values to mybox1's instance variables<br /> mybox1.width = 10;<br /> mybox1.height = 20;<br /> mybox1.depth = 15;<br /> /* assign different values to mybox2's<br /> instance variables */<br /> mybox2.width = 3;<br /> mybox2.height = 6;<br /> mybox2.depth = 9;<br /> // get volume of first box<br /> vol = mybox1.volume();<br /> System.out.println("Volume is " + vol);<br /> // get volume of second box<br /> vol = mybox2.volume();<br /> System.out.println("Volume is " + vol);</div> <div>780 Java™ 2: The Complete Reference<br /> if(debug.getState())<br /> g.drawString("Debug is on.", 10, 220);<br /> else<br /> g.drawString("Debug is off.", 10, 220);<br /> }<br /> }<br /> if(test.getState())<br /> g.drawString("Testing is on.", 10, 240);<br /> else<br /> g.drawString("Testing is off.", 10, 240);<br /> class MyWindowAdapter extends WindowAdapter {<br /> MenuFrame menuFrame;<br /> public MyWindowAdapter(MenuFrame menuFrame) {<br /> this.menuFrame = menuFrame;<br /> }<br /> public void windowClosing(WindowEvent we) {<br /> menuFrame.setVisible(false);<br /> }<br /> }<br /> class MyMenuHandler implements ActionListener, ItemListener {<br /> MenuFrame menuFrame;<br /> public MyMenuHandler(MenuFrame menuFrame) {<br /> this.menuFrame = menuFrame;<br /> }<br /> // Handle action events<br /> public void actionPerformed(ActionEvent ae) {<br /> String msg = "You selected ";<br /> String arg = (String)ae.getActionCommand();<br /> if(arg.equals("New..."))<br /> msg += "New.";<br /> else if(arg.equals("Open..."))<br /> msg += "Open.";<br /> else if(arg.equals("Close"))<br /> msg += "Close.";<br /> else if(arg.equals("Quit..."))<br /> msg += "Quit.";<br /> else if(arg.equals("Edit"))<br /> msg += "Edit.";</div> <div>APPLYING JAVA<br /> Chapter 29: The DynamicBillboard Applet 1031<br /> int seed = (int)System.currentTimeMillis();<br /> int denominator = 10;<br /> while((new_pixels_per_cell % denominator > 0 ||<br /> cell_h % denominator == 0) && denominator > 1) {<br /> --denominator;<br /> }<br /> int new_randoms_per_cell = new_pixels_per_cell / denominator;<br /> int new_randoms = rounded_new_pixels_per_cell / denominator;<br /> for(int p = 0; p < new_randoms_per_cell; ++p) {<br /> seed *= MULTIPLIER;<br /> cell = (seed >>> 29);<br /> random[cell][random_count[cell]++] = (short)p;<br /> }<br /> seed += 0x5050;<br /> try { Thread.sleep(150); } catch (InterruptedException e) {}<br /> for(int p = new_randoms_per_cell; p < new_randoms; ++p) {<br /> seed *= MULTIPLIER;<br /> cell = (seed >>> 29);<br /> }<br /> while(random_count[cell] >= new_randoms_per_cell) {<br /> if(++cell >= total_cells) {<br /> cell = 0;<br /> }<br /> }<br /> random[cell][random_count[cell]++] = (short)p;<br /> for(int s = 0; s < CELLS; ++s) {<br /> for(int ps = new_randoms_per_cell; ps < new_pixels_per_cell;<br /> ps += new_randoms_per_cell) {<br /> }<br /> int offset = ps * total_cells;<br /> for(int p = 0; p < new_randoms_per_cell; ++p) {<br /> random[s][ps + p] = (short)(random[s][p] + offset);<br /> }</div> <div>688 Java™ 2: The Complete Reference<br /> The Abstract Window Toolkit (AWT) was introduced in Chapter 19 because it<br /> provides support for applets. This chapter begins its in-depth examination.<br /> The AWT contains numerous classes and methods that allow you to create<br /> and manage windows. A full description of the AWT would easily fill an entire book.<br /> Therefore, it is not possible to describe in detail every method, instance variable, or<br /> class contained in the AWT. However, this and the following two chapters explain<br /> the techniques needed to effectively use the AWT when creating your own applets or<br /> stand-alone programs. From there, you will be able to explore other parts of the AWT<br /> on your own.<br /> In this chapter, you will learn how to create and manage windows, manage fonts,<br /> output text, and utilize graphics. Chapter 22 describes the various controls, such as<br /> scroll bars and push buttons, supported by the AWT. It also explains further aspects of<br /> Java’s event-handling mechanism. Chapter 23 examines the AWT’s imaging subsystem<br /> and animation.<br /> Although the main purpose of the AWT is to support applet windows, it can<br /> also be used to create stand-alone windows that run in a GUI environment, such as<br /> Windows. Most of the examples are contained in applets, so to run them, you need<br /> to use an applet viewer or a Java-compatible Web browser. A few examples will<br /> demonstrate the creation of stand-alone, windowed programs.<br /> If you have not yet read Chapter 20, please do so now. It provides an overview of event<br /> handling, which is used by many of the examples in this chapter.<br /> AWT Classes<br /> The AWT classes are contained in the java.awt package. It is one of Java’s largest<br /> packages. Fortunately, because it is logically organized in a top-down, hierarchical<br /> fashion, it is easier to understand and use than you might at first believe. Table 21-1<br /> lists some of the many AWT classes.<br /> Class<br /> AWTEvent<br /> AWTEventMulticaster<br /> BorderLayout<br /> Button<br /> Description<br /> Encapsulates AWT events.<br /> Dispatches events to multiple listeners.<br /> The border layout manager. Border layouts use five<br /> components: North, South, East, West, and Center.<br /> Creates a push button control.<br /> Table 21-1.<br /> Some AWT Classes</div> <div>880 Java™ 2: The Complete Reference<br /> The argument style is one of the following values: DEFAULT, SHORT, MEDIUM,<br /> LONG, or FULL. These are int constants defined by DateFormat. They cause<br /> different details about the time to be presented. The argument locale is one of the<br /> static references defined by Locale. If the style and/or locale is not specified,<br /> defaults are used.<br /> The following listing illustrates how to format time information. It begins by<br /> creating a Date object. This captures the current date and time information and then<br /> outputs the time information by using different styles and locales.<br /> // Demonstrate time formats.<br /> import java.text.*;<br /> import java.util.*;<br /> public class TimeFormatDemo {<br /> public static void main(String args[]) {<br /> Date date = new Date();<br /> DateFormat df;<br /> df = DateFormat.getTimeInstance(DateFormat.SHORT, Locale.JAPAN);<br /> System.out.println("Japan: " + df.format(date));<br /> df = DateFormat.getTimeInstance(DateFormat.LONG, Locale.UK);<br /> System.out.println("United Kingdom: " + df.format(date));<br /> }<br /> }<br /> df = DateFormat.getTimeInstance(DateFormat.FULL, Locale.CANADA);<br /> System.out.println("Canada: " + df.format(date));<br /> Sample output from this program is shown here:<br /> Japan: 20:25<br /> United Kingdom: 20:25:14 CDT<br /> Canada: 8:25:14 o'clock PM CDT<br /> The DateFormat class also has a getDateTimeInstance( ) method that can format<br /> both date and time information. You may wish to experiment with it on your own.<br /> SimpleDateFormat Class<br /> SimpleDateFormat is a concrete subclass of DateFormat. It allows you to define your<br /> own formatting patterns that are used to display date and time information.<br /> One of its constructors is shown here:<br /> SimpleDateFormat(String formatString)</div> <div>1040 Java™ 2: The Complete Reference<br /> UnrollTransition.java<br /> UnrollTransition makes it appear as if a rolled-up poster is placed on the bottom of the<br /> applet and then unrolled upward, gradually revealing the next image and covering<br /> the old image. To enhance the unroll illusion, the roll gradually decreases in size as it<br /> makes its way upward on the billboard.<br /> Two instance variables are used during the creation of unroll transitions. The<br /> location variable references pixels within the pixel arrays. It stores the current pixel<br /> that the roll first appears on. The unroll_amount array variable tells the class how<br /> many vertical pixels the roll should move upward each frame.<br /> The most difficult part of creating each cell frame is drawing the roll. The only<br /> other task that needs to be completed each frame is to draw the pixels from the new<br /> image onto the space vacated by the roll from the previous frame.<br /> The roll is drawn with scan lines from the new image. The first line of the roll is<br /> drawn with the scan line located at the Y coordinate above the roll’s Y coordinate on<br /> the applet. For example, if the roll is located on line ten for a particular cell frame,<br /> then line nine of the new image will be used to draw the first line of the roll. Each<br /> subsequent line of the roll is drawn using a line from the image located above the<br /> previous line of the new image. So, continuing the example, the second line of the roll<br /> will be drawn using line eight of the new image.<br /> The roll is painted with its 3-D appearance by drawing each line of the roll with a<br /> slight offset to the left. Lines closer to the center of the roll are drawn with a larger<br /> offset than lines close to the top and bottom. The top and bottom lines of the rolls are<br /> then shaded to make it look as if a light were above the applet. This results in the top<br /> line being a bit brighter than the rest of the roll and the bottom line being a bit darker.<br /> createUnrollAmountArray( )<br /> Each consecutive cell frame in this transition unrolls the roll onto the applet a little<br /> bit less than the previous cell frame. The createUnrollAmountArray( ) static method<br /> is used to calculate an array that indicates how much each cell frame should unroll<br /> the roll.<br /> init( )<br /> The init( ) method for this transition starts like all other transitions, with a call to the<br /> base class’ init( ) method. Then the location variable is initialized to an index past the<br /> last pixel in a pixel array. This is followed by copying all of the old billboard’s pixels<br /> into the work_pixels array.</div> <div>1104 Java™ 2: The Complete Reference<br /> {w3, bg, bg, l2, bg, bg, bg, w2}<br /> };<br /> private Dimension checksize() {<br /> Dimension d = getSize();<br /> int w = d.width;<br /> int h = d.height;<br /> if (w < 1 || h < 1)<br /> return d;<br /> if ((offscreen == null) ||<br /> (w != offscreensize.width) ||<br /> (h != offscreensize.height)) {<br /> System.out.println("updating board: " + w + " x " + h + "\r");<br /> offscreen = createImage(w, h);<br /> offscreensize = d;<br /> offGraphics = offscreen.getGraphics();<br /> offscreen2 = createImage(w, h);<br /> offGraphics2 = offscreen2.getGraphics();<br /> offGraphics.setColor(Color.white);<br /> offGraphics.fillRect(0,0,w,h);<br /> // lt is the thickness of the white lines between tiles.<br /> // gaps is the sum of all the whitespace.<br /> // lw, lh are the dimensions of the tiles.<br /> // aw, ah are the dimensions of the entire board<br /> // lm, tmare the left and top margin to center aw, ah in the applet.<br /> lt = 1 + w / 400;<br /> int gaps = lt * 20;<br /> lw = (w - gaps) / 15;<br /> lh = (h - gaps - lt * 2) / 16; // compensating for tray height;<br /> aw = lw * 15 + gaps;<br /> ah = lh * 15 + gaps;<br /> lm = (w - aw) / 2 + lt;<br /> tm = (h - ah - (lt * 2 + lh)) / 2 + lt;</div> <div>170 Java™ 2: The Complete Reference<br /> The output from this program is shown here:<br /> Factorial of 3 is 6<br /> Factorial of 4 is 24<br /> Factorial of 5 is 120<br /> If you are unfamiliar with recursive methods, then the operation of fact( ) may<br /> seem a bit confusing. Here is how it works. When fact( ) is called with an argument of<br /> 1, the function returns 1; otherwise it returns the product of fact(n–1)*n. To evaluate<br /> this expression, fact( ) is called with n–1. This process repeats until n equals 1 and the<br /> calls to the method begin returning.<br /> To better understand how the fact( ) method works, let’s go through a short<br /> example. When you compute the factorial of 3, the first call to fact( ) will cause a<br /> second call to be made with an argument of 2. This invocation will cause fact( ) to<br /> be called a third time with an argument of 1. This call will return 1, which is then<br /> multiplied by 2 (the value of n in the second invocation). This result (which is 2) is<br /> then returned to the original invocation of fact( ) and multiplied by 3 (the original<br /> value of n). This yields the answer, 6. You might find it interesting to insert println( )<br /> statements into fact( ) which will show at what level each call is and what the<br /> intermediate answers are.<br /> When a method calls itself, new local variables and parameters are allocated<br /> storage on the stack, and the method code is executed with these new variables<br /> from the start. A recursive call does not make a new copy of the method. Only<br /> the arguments are new. As each recursive call returns, the old local variables and<br /> parameters are removed from the stack, and execution resumes at the point of the<br /> call inside the method. Recursive methods could be said to “telescope” out and back.<br /> Recursive versions of many routines may execute a bit more slowly than the<br /> iterative equivalent because of the added overhead of the additional function calls.<br /> Many recursive calls to a method could cause a stack overrun. Because storage for<br /> parameters and local variables is on the stack and each new call creates a new copy of<br /> these variables, it is possible that the stack could be exhausted. If this occurs, the Java<br /> run-time system will cause an exception. However, you probably will not have to<br /> worry about this unless a recursive routine runs wild.<br /> The main advantage to recursive methods is that they can be used to create clearer<br /> and simpler versions of several algorithms than can their iterative relatives. For<br /> example, the QuickSort sorting algorithm is quite difficult to implement in an iterative<br /> way. Some problems, especially AI-related ones, seem to lend themselves to recursive<br /> solutions. Finally, some people seem to think recursively more easily than iteratively.<br /> When writing recursive methods, you must have an if statement somewhere to<br /> force the method to return without the recursive call being executed. If you don’t do<br /> this, once you call the method, it will never return. This is a very common error in<br /> working with recursion. Use println( ) statements liberally during development so that</div> <div>THE JAVA LIBRARY<br /> Chapter 18: Networking 625<br /> class WriteServer {<br /> public static int serverPort = 998;<br /> public static int clientPort = 999;<br /> public static int buffer_size = 1024;<br /> public static DatagramSocket ds;<br /> public static byte buffer[] = new byte[buffer_size];<br /> public static void TheServer() throws Exception {<br /> int pos=0;<br /> while (true) {<br /> int c = System.in.read();<br /> switch (c) {<br /> case -1:<br /> System.out.println("Server Quits.");<br /> return;<br /> case '\r':<br /> break;<br /> case '\n':<br /> ds.send(new DatagramPacket(buffer,pos,<br /> InetAddress.getLocalHost(),clientPort));<br /> pos=0;<br /> break;<br /> default:<br /> buffer[pos++] = (byte) c;<br /> }<br /> }<br /> }<br /> public static void TheClient() throws Exception {<br /> while(true) {<br /> DatagramPacket p = new DatagramPacket(buffer, buffer.length);<br /> ds.receive(p);<br /> System.out.println(new String(p.getData(), 0, p.getLength()));<br /> }<br /> }<br /> public static void main(String args[]) throws Exception {<br /> if(args.length == 1) {<br /> ds = new DatagramSocket(serverPort);<br /> TheServer();<br /> } else {</div> <div>992 Java™ 2: The Complete Reference<br /> int main()<br /> {<br /> Coord ob1, ob2;<br /> ob1.x = 10;<br /> ob1.y = 20;<br /> ob2.x = 88;<br /> ob2.y = 99;<br /> cout << "Original values:\n";<br /> cout << "ob1: " << ob1.x << ", " << ob1.y << "\n";<br /> cout << "ob2: " << ob2.x << ", " << ob2.y << "\n";<br /> cout << "\n";<br /> swap(ob1, ob2);<br /> cout << "Swapped values:\n";<br /> cout << "ob1: " << ob1.x << ", " << ob1.y << "\n";<br /> cout << "ob2: " << ob2.x << ", " << ob2.y << "\n";<br /> }<br /> return 0;<br /> Following is the output produced by this program. As you can see, the contents of<br /> ob1 and ob2 have been exchanged:<br /> Original values:<br /> ob1: 10, 20<br /> ob2: 88, 99<br /> Swapped values:<br /> ob1: 88, 99<br /> ob2: 10, 20<br /> In Java, all objects are accessed via an object reference variable. Thus, when an<br /> object is passed to a method, only its reference is passed. This means that all objects<br /> are automatically passed by reference to a Java method. Without thinking any deeper<br /> about what is actually occurring, someone might initially try the following (incorrect)<br /> conversion of the preceding program:</div> <div>THE JAVA LIBRARY<br /> Chapter 22: Using AWT Controls, Layout Managers, and Menus 783<br /> all input is directed to it until it is closed. This means that you cannot access other parts<br /> of your program until you have closed the dialog box. When a modeless dialog box is<br /> active, input focus can be directed to another window in your program. Thus, other<br /> parts of your program remain active and accessible. Dialog boxes are of type Dialog.<br /> Two commonly used constructors are shown here:<br /> Dialog(Frame parentWindow, boolean mode)<br /> Dialog(Frame parentWindow, String title, boolean mode)<br /> Here, parentWindow is the owner of the dialog box. If mode is true, the dialog box is modal.<br /> Otherwise, it is modeless. The title of the dialog box can be passed in title. Generally, you<br /> will subclass Dialog, adding the functionality required by your application.<br /> Following is a modified version of the preceding menu program that displays a<br /> modeless dialog box when the New option is chosen. Notice that when the dialog box<br /> is closed, dispose( ) is called. This method is defined by Window, and it frees all system<br /> resources associated with the dialog box window.<br /> // Demonstrate Dialog box.<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import java.applet.*;<br /> /*<br /> <applet code="DialogDemo" width=250 height=250><br /> </applet><br /> */<br /> // Create a subclass of Dialog.<br /> class SampleDialog extends Dialog implements ActionListener {<br /> SampleDialog(Frame parent, String title) {<br /> super(parent, title, false);<br /> setLayout(new FlowLayout());<br /> setSize(300, 200);<br /> }<br /> add(new Label("Press this button:"));<br /> Button b;<br /> add(b = new Button("Cancel"));<br /> b.addActionListener(this);<br /> public void actionPerformed(ActionEvent ae) {<br /> dispose();<br /> }</div> <div>THE JAVA LIBRARY<br /> Chapter 14: Exploring java.lang 385<br /> Method<br /> int intValue( )<br /> boolean isInfinite( )<br /> static boolean isInfinite(double num)<br /> boolean isNaN( )<br /> static boolean isNaN(double num)<br /> static double longBitsToDouble(long num)<br /> long longValue( )<br /> static double parseDouble(String str)<br /> throws NumberFormatException<br /> short shortValue( )<br /> String toString( )<br /> static String toString(double num)<br /> static Double valueOf(String str)<br /> throws NumberFormatException<br /> Description<br /> Returns the value of the invoking<br /> object as an int.<br /> Returns true if the invoking object<br /> contains an infinite value.<br /> Otherwise, it returns false.<br /> Returns true if num specifies an<br /> infinite value. Otherwise, it<br /> returns false.<br /> Returns true if the invoking object<br /> contains a value that is not a<br /> number. Otherwise, it returns false.<br /> Returns true if num specifies a<br /> value that is not a number.<br /> Otherwise, it returns false.<br /> Returns double equivalent of the<br /> IEEE-compatible, double-precision<br /> bit pattern specified by num.<br /> Returns the value of the invoking<br /> object as a long.<br /> Returns the double equivalent of<br /> the number contained in the string<br /> specified by str using radix 10.<br /> (Added by Java 2)<br /> Returns the value of the invoking<br /> object as a short.<br /> Returns the string equivalent of the<br /> invoking object.<br /> Returns the string equivalent of the<br /> value specified by num.<br /> Returns a Double object that<br /> contains the value specified by the<br /> string in str.<br /> Table 14-2.<br /> The Methods Defined by Double (continued)</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 28: Migrating from C++ to Java 987<br /> to the Coord object that will be reversed. As you can see, C++’s *, &, and -> pointer<br /> operators are used to perform the operation.<br /> // Reverse the signs of a coordinate - C++ version.<br /> #include <iostream><br /> using namespace std;<br /> class Coord {<br /> public:<br /> int x;<br /> int y;<br /> };<br /> // Reverse the sign of the coordinates.<br /> void reverseSign(Coord *ob) {<br /> ob->x = -ob->x;<br /> ob->y = -ob->y;<br /> }<br /> int main()<br /> {<br /> Coord ob;<br /> ob.x = 10;<br /> ob.y = 20;<br /> cout << "Original values for ob: ";<br /> cout << ob.x << ", " << ob.y << "\n";<br /> reverseSign(&ob);<br /> cout << "Sign reversed values for ob: ";<br /> cout << ob.x << ", " << ob.y << "\n";<br /> return 0;<br /> }</div> <div>THE JAVA LIBRARY<br /> Chapter 24: New I/O, Regular Expressions, and Other Packages 863<br /> matches( ) returns true. Next, a new Matcher is created with the input sequence “Java 2”<br /> and matches( ) is called again. In this case, the pattern and the input sequence differ,<br /> and no match is found. Remember, the matches( ) function returns true only when the<br /> input sequence precisely matches the pattern. It will not return true just because a<br /> subsequence matches.<br /> You can use find( ) to determine if the input sequence contains a subsequence that<br /> matches the pattern. Consider the following program.<br /> // Use find() to find a subsequence.<br /> import java.util.regex.*;<br /> class RegExpr2 {<br /> public static void main(String args[]) {<br /> Pattern pat = Pattern.compile("Java");<br /> Matcher mat = pat.matcher("Java 2");<br /> System.out.println("Looking for Java in Java 2.");<br /> }<br /> }<br /> if(mat.find()) System.out.println("subsequence found");<br /> else System.out.println("No Match");<br /> The output is shown here:<br /> Looking for Java in Java 2.<br /> subsequence found<br /> In this case, find( ) finds the subsequence “Java”.<br /> The find( ) method can be used to search the input sequence for repeated occurrences<br /> of the pattern because each call to find( ) picks up where the previous one left off. For<br /> example, the following program finds two occurrences of the pattern “test”.<br /> // Use find() to find multiple subsequences.<br /> import java.util.regex.*;<br /> class RegExpr3 {<br /> public static void main(String args[]) {<br /> Pattern pat = Pattern.compile("test");<br /> Matcher mat = pat.matcher("test 1 2 3 test");</div> <div>This page intentionally left blank.</div> <div>962 Java™ 2: The Complete Reference<br /> // Get enumeration of parameter names.<br /> Enumeration e = request.getParameterNames();<br /> }<br /> }<br /> // Display parameter names and values.<br /> while(e.hasMoreElements()) {<br /> String pname = (String)e.nextElement();<br /> pw.print(pname + " = ");<br /> String pvalue = request.getParameter(pname);<br /> pw.println(pvalue);<br /> }<br /> pw.close();<br /> Compile the servlet and perform these steps to test this example:<br /> 1. Start Tomcat (if it is not already running).<br /> 2. Display the Web page in a browser.<br /> 3. Enter an employee name and phone number in the text fields.<br /> 4. Submit the Web page.<br /> After following these steps, the browser will display a response that is dynamically<br /> generated by the servlet.<br /> The javax.servlet.http Package<br /> The javax.servlet.http package contains a number of interfaces and classes that are<br /> commonly used by servlet developers. You will see that its functionality makes it easy<br /> to build servlets that work with HTTP requests and responses.<br /> The following table summarizes the core interfaces that are provided in this package:<br /> Interface<br /> HttpServletRequest<br /> HttpServletResponse<br /> HttpSession<br /> HttpSessionBindingListener<br /> Description<br /> Enables servlets to read data from an HTTP request.<br /> Enables servlets to write data to an HTTP response.<br /> Allows session data to be read and written.<br /> Informs an object that it is bound to or unbound<br /> from a session.</div> <div>856 Java™ 2: The Complete Reference<br /> mBuf = ByteBuffer.allocateDirect(26);<br /> // Write some bytes to the buffer.<br /> for(int i=0; i<26; i++)<br /> mBuf.put((byte)('A' + i));<br /> // Rewind the buffer so that it can written.<br /> mBuf.rewind();<br /> // Write the buffer to the output file.<br /> fChan.write(mBuf);<br /> }<br /> }<br /> // close channel and file.<br /> fChan.close();<br /> fOut.close();<br /> } catch (IOException exc) {<br /> System.out.println(exc);<br /> System.exit(1);<br /> }<br /> The call to rewind( ) on mBuf is necessary in order to reset the current position to zero<br /> after data has been written to mBuf. Remember, each call to put( ) advances the current<br /> position. Therefore, it is necessary for the current position to be reset to the start of the<br /> buffer before calling write( ). If this is not done, write( ) will think that there is no data<br /> in the buffer.<br /> To write to a file using a mapped file, follow these steps. First, open the file for<br /> read/write operations. Next, map that file to a buffer by calling map( ). Then, write<br /> to the buffer. Because the buffer is mapped to the file, any changes to that buffer are<br /> automatically reflected in the file. Thus, no explicit write operations to the channel<br /> are necessary. Here is the preceding program reworked so that a mapped file is used.<br /> Notice that the file is opened as a RandomAccessFile. This is necessary to allow the<br /> file to be read and written.<br /> // Write to a mapped file.<br /> import java.io.*;<br /> import java.nio.*;<br /> import java.nio.channels.*;<br /> public class MappedChannelWrite {</div> <div>924 Java™ 2: The Complete Reference<br /> The ImageIcon class implements the Icon interface that declares the methods<br /> shown here:<br /> Method<br /> int getIconHeight( )<br /> int getIconWidth( )<br /> void paintIcon(Component comp, Graphics g,<br /> int x, int y)<br /> Description<br /> Returns the height of the icon<br /> in pixels.<br /> Returns the width of the icon<br /> in pixels.<br /> Paints the icon at position x, y on<br /> the graphics context g. Additional<br /> information about the paint<br /> operation can be provided in comp.<br /> Swing labels are instances of the JLabel class, which extends JComponent. It can<br /> display text and/or an icon. Some of its constructors are shown here:<br /> JLabel(Icon i)<br /> Label(String s)<br /> JLabel(String s, Icon i, int align)<br /> Here, s and i are the text and icon used for the label. The align argument is either LEFT,<br /> RIGHT, CENTER, LEADING, or TRAILING. These constants are defined in the<br /> SwingConstants interface, along with several others used by the Swing classes.<br /> The icon and text associated with the label can be read and written by the<br /> following methods:<br /> Icon getIcon( )<br /> String getText( )<br /> void setIcon(Icon i)<br /> void setText(String s)<br /> Here, i and s are the icon and text, respectively.<br /> The following example illustrates how to create and display a label containing both<br /> an icon and a string. The applet begins by getting its content pane. Next, an ImageIcon<br /> object is created for the file france.gif. This is used as the second argument to the<br /> JLabel constructor. The first and last arguments for the JLabel constructor are the label<br /> text and the alignment. Finally, the label is added to the content pane.<br /> import java.awt.*;<br /> import javax.swing.*;<br /> /*</div> <div>164 Java™ 2.0: The Complete Reference<br /> }<br /> // constructor used when all dimensions specified<br /> Box(double w, double h, double d) {<br /> width = w;<br /> height = h;<br /> depth = d;<br /> }<br /> // constructor used when no dimensions specified<br /> Box() {<br /> width = -1; // use -1 to indicate<br /> height = -1; // an uninitialized<br /> depth = -1; // box<br /> }<br /> // constructor used when cube is created<br /> Box(double len) {<br /> width = height = depth = len;<br /> }<br /> // compute and return volume<br /> double volume() {<br /> return width * height * depth;<br /> }<br /> class OverloadCons2 {<br /> public static void main(String args[]) {<br /> // create boxes using the various constructors<br /> Box mybox1 = new Box(10, 20, 15);<br /> Box mybox2 = new Box();<br /> Box mycube = new Box(7);<br /> Box myclone = new Box(mybox1);<br /> double vol;<br /> // get volume of first box<br /> vol = mybox1.volume();<br /> System.out.println("Volume of mybox1 is " + vol);</div> <div>This page intentionally left blank.</div> <div>THE JAVA LIBRARY<br /> Chapter 14: Exploring java.lang 393<br /> Method<br /> static String toString(int num, int radix)<br /> static Integer valueOf(String str)<br /> throws NumberFormatException<br /> static Integer valueOf(String str, int radix)<br /> throws NumberFormatException<br /> Description<br /> Returns a string that contains the<br /> decimal equivalent of num using<br /> the specified radix.<br /> Returns an Integer object that<br /> contains the value specified by<br /> the string in str.<br /> Returns an Integer object that<br /> contains the value specified by<br /> the string in str using the<br /> specified radix.<br /> Table 14-5.<br /> The Methods Defined by Integer (continued)<br /> Method<br /> byte byteValue( )<br /> int compareTo(Long l)<br /> int compareTo(Object obj)<br /> Description<br /> Returns the value of the invoking<br /> object as a byte.<br /> Compares the numerical value of<br /> the invoking object with that of l.<br /> Returns 0 if the values are equal.<br /> Returns a negative value if the<br /> invoking object has a lower<br /> value. Returns a positive value if<br /> the invoking object has a greater<br /> value. (Added by Java 2)<br /> Operates identically to<br /> compareTo(Long) if obj is of<br /> class Long. Otherwise, throws a<br /> ClassCastException. (Added by<br /> Java 2)<br /> Table 14-6.<br /> The Methods Defined by Long</div> <div>1142 Java™ 2: The Complete Reference<br /> addCookie( ), 965, 967, 975<br /> addElement( ), 486, 488<br /> addFirst( ), 453<br /> addImage( ), 811<br /> addLast( ), 453, 454<br /> addMouseListener( ), 676<br /> addMouseMotionListener( ), 676<br /> addTypeListener( ), 655–656<br /> AdjustmentEvent class, 657,<br /> 659–660, 756<br /> AdjustmentListener interface, 669,<br /> 670, 756<br /> adjustmentValueChanged( ), 670<br /> after( ), 512, 514<br /> Algorithms, collection, 441,<br /> 475–480<br /> ALIGN, 644<br /> allocate( ), 850, 851–852<br /> ALT, 643<br /> AND operator<br /> bitwise (&), 80, 82<br /> Boolean logical (&), 92, 94<br /> short-circuit (&&), 92, 93–94<br /> Animation, cell, 837–841<br /> Apache Software Foundation, 951<br /> append( ), 372–373, 762<br /> Applet, 10, 328–331<br /> architecture, 632<br /> basics, 628–629<br /> colors, setting and<br /> obtaining, 636–638<br /> executing, 330–331<br /> and the Internet, 10<br /> and main( ), 29, 131, 329, 331<br /> outputting to console, 652<br /> passing parameters to,<br /> 644–649<br /> request for repaint, 638–641<br /> skeleton, 632–635<br /> and socket connections, 595<br /> string output to, 636<br /> versus application, 10<br /> viewer, 330–331<br /> Applet class, 329, 628–652, 692<br /> methods, table of, 629–631<br /> applet package, 314, 328<br /> applet tag, 16<br /> APPLET tag, HTML, 330–331,<br /> 628–629<br /> full syntax for, 643–644<br /> AppletContext interface, 628,<br /> 649–651, 1048<br /> methods, table of, 650<br /> AppletStub interface, 628, 652<br /> appletviewer, 330, 628<br /> status window, using, 642<br /> Application builder tools, 887–888<br /> Application versus applet, 10<br /> AreaAveragingScaleFilter class, 821<br /> areFieldsSet, 514<br /> Arguments, 138, 143<br /> command-line, 188<br /> passing, 165–167<br /> Arithmetic operators, 74–80<br /> ArithmeticException, 252, 253, 265<br /> Array(s), 28, 61–70<br /> boundary checks, 64<br /> copying, 408, 411<br /> declaration syntax,<br /> alternative, 70<br /> dynamic, 449–451, 485<br /> initializing, 63–64, 68–69<br /> length instance variable of,<br /> 179–181<br /> multidimensional, 64–70<br /> one-dimensional, 61–64<br /> of strings, 187<br /> and strings, 52, 70<br /> arraycopy( ), 408, 411<br /> ArrayIndexOutOfBoundsExceptio<br /> n, 256, 265, 482, 483<br /> ArrayList class, 448, 449–452, 462<br /> Arrays class, 480–484<br /> ArrayStoreException, 265<br /> ASCII character set, 47, 48, 51<br /> and the Internet, 350, 356<br /> asin( ), 420<br /> asList( ), 480<br /> Assembly language, 4, 5<br /> assert( ), 16, 39, 340–343<br /> Assertion, 340–344<br /> AssertionError, 340<br /> Assignment operator(s)<br /> =, 31, 94–95<br /> arithmetic (op=), 74, 76–78<br /> bitwise, 80, 89–90<br /> Boolean, 92<br /> atan( ), 420<br /> atan2( ), 420<br /> AudioClip interface, 628, 651<br /> available( ), 548<br /> AWT. See Abstract Window Toolkit<br /> AWTEvent class, 656–657<br /> bit mask constants, 791<br /> B<br /> B, 4, 5<br /> BASIC, 5<br /> BCPL, 5<br /> Bean Builder, 888, 911–920<br /> Bean Developer Kit (BDK), 888–891<br /> BeanBox, 888<br /> BeanDescriptor class, 907, 909–911<br /> BeanInfo interface, 903–904, 907,<br /> 910–911<br /> Beans, Java. See Java Beans<br /> before( ), 512, 514<br /> Bell curve, 525<br /> Berkeley Software Distribution<br /> (BSD), 588<br /> Berners-Lee, Tim, 597<br /> Beyond Photography, The Digital<br /> Darkroom (Holzmann), 816<br /> binarySearch( ), 481<br /> BitSet class, 508–511<br /> methods, table of, 508–510<br /> Bitwise operators, 80–90<br /> Blocks, code. See Code blocks<br /> Boolean<br /> literals, 51<br /> logical operators, 92–94<br /> Boolean class, 401<br /> methods, table of, 401<br /> boolean data type, 42, 48–49<br /> and relational operators, 91<br /> BorderLayout class, 766–768<br /> Borenstein, Nat, 602<br /> break statement, 100, 104, 105–107,<br /> 120–124<br /> as form of goto, 122–124<br /> Buffer class, 847–850<br /> methods, table of, 848<br /> Buffer(s), NIO, 847–850<br /> BufferedInputStream class, 316,<br /> 555–557<br /> BufferedOutputStream class, 316,<br /> 557<br /> BufferedReader class, 318–319, 320,<br /> 321, 569–570<br /> BufferedWriter class, 570–571<br /> Buffering, double, 807–811<br /> Button class, 739<br /> extending, 792<br /> Buttons, Swing, 927–934<br /> Byte class, 387, 396, 397<br /> methods defined by, table<br /> of, 387–389<br /> byte data type, 42, 43, 44, 50<br /> ByteArrayInputStream class,<br /> 552–553<br /> ByteArrayOutputStream class,<br /> 553–554<br /> ByteBuffer class, 848–850, 851, 852<br /> get( ) and put( ) methods,<br /> table of, 849<br /> Bytecode, 11–12, 14, 26, 422<br /> byteValue( ), 381</div> <div>THE JAVA LIBRARY<br /> Chapter 15: java.util Part 1: The Collections Framework 479<br /> Method<br /> static Map unmodifiableMap(Map m)<br /> static Set unmodifiableSet(Set s)<br /> static SortedMap<br /> unmodifiableSortedMap(SortedMap sm)<br /> static SortedSet<br /> unmodifiableSortedSet(SortedSet ss)<br /> Description<br /> Returns an unmodifiable map<br /> backed by m.<br /> Returns an unmodifiable set<br /> backed by s.<br /> Returns an unmodifiable sorted<br /> map backed by sm.<br /> Returns an unmodifiable sorted<br /> set backed by ss.<br /> Table 15-9.<br /> The Algorithms Defined by Collections (continued)<br /> Collections defines three static variables: EMPTY_SET, EMPTY_LIST, and<br /> EMPTY_MAP. All are immutable. EMPTY_MAP was added by Java 2, version 1.3.<br /> The following program demonstrates some of the algorithms. It creates and<br /> initializes a linked list. The reverseOrder( ) method returns a Comparator that reverses<br /> the comparison of Integer objects. The list elements are sorted according to this<br /> comparator and then are displayed. Next, the list is randomized by calling shuffle( ),<br /> and then its minimum and maximum values are displayed.<br /> // Demonstrate various algorithms.<br /> import java.util.*;<br /> class AlgorithmsDemo {<br /> public static void main(String args[]) {<br /> // Create and initialize linked list<br /> LinkedList ll = new LinkedList();<br /> ll.add(new Integer(-8));<br /> ll.add(new Integer(20));<br /> ll.add(new Integer(-20));<br /> ll.add(new Integer(8));<br /> // Create a reverse order comparator<br /> Comparator r = Collections.reverseOrder();<br /> // Sort list by using the comparator<br /> Collections.sort(ll, r);</div> <div>232 Java™ 2: The Complete Reference<br /> // Instantiate the various classes in p1.<br /> public class Demo {<br /> public static void main(String args[]) {<br /> Protection ob1 = new Protection();<br /> Derived ob2 = new Derived();<br /> SamePackage ob3 = new SamePackage();<br /> }<br /> }<br /> The test file for p2 is shown next:<br /> // Demo package p2.<br /> package p2;<br /> // Instantiate the various classes in p2.<br /> public class Demo {<br /> public static void main(String args[]) {<br /> Protection2 ob1 = new Protection2();<br /> OtherPackage ob2 = new OtherPackage();<br /> }<br /> }<br /> Importing Packages<br /> Given that packages exist and are a good mechanism for compartmentalizing diverse<br /> classes from each other, it is easy to see why all of the built-in Java classes are stored in<br /> packages. There are no core Java classes in the unnamed default package; all of the<br /> standard classes are stored in some named package. Since classes within packages<br /> must be fully qualified with their package name or names, it could become tedious to<br /> type in the long dot-separated package path name for every class you want to use.<br /> For this reason, Java includes the import statement to bring certain classes, or entire<br /> packages, into visibility. Once imported, a class can be referred to directly, using only<br /> its name. The import statement is a convenience to the programmer and is not<br /> technically needed to write a complete Java program. If you are going to refer to a<br /> few dozen classes in your application, however, the import statement will save a lot<br /> of typing.<br /> In a Java source file, import statements occur immediately following the package<br /> statement (if it exists) and before any class definitions. This is the general form of the<br /> import statement:<br /> import pkg1[.pkg2].(classname|*);</div> <div>THE JAVA LIBRARY<br /> Chapter 14: Exploring java.lang 405<br /> Let’s look at two of the most common uses of the Runtime class: memory<br /> management and executing additional processes.<br /> Memory Management<br /> Although Java provides automatic garbage collection, sometimes you will want to<br /> know how large the object heap is and how much of it is left. You can use this<br /> information, for example, to check your code for efficiency or to approximate how<br /> many more objects of a certain type can be instantiated. To obtain these values, use the<br /> totalMemory( ) and freeMemory( ) methods.<br /> As we mentioned in Part I, Java’s garbage collector runs periodically to recycle<br /> unused objects. However, sometimes you will want to collect discarded objects prior to<br /> the collector’s next appointed rounds. You can run the garbage collector on demand by<br /> calling the gc( ) method. A good thing to try is to call gc( ) and then call freeMemory( )<br /> to get a baseline memory usage. Next, execute your code and call freeMemory( ) again<br /> to see how much memory it is allocating. The following program illustrates this idea:<br /> // Demonstrate totalMemory(), freeMemory() and gc().<br /> class MemoryDemo {<br /> public static void main(String args[]) {<br /> Runtime r = Runtime.getRuntime();<br /> long mem1, mem2;<br /> Integer someints[] = new Integer[1000];<br /> System.out.println("Total memory is: " +<br /> r.totalMemory());<br /> mem1 = r.freeMemory();<br /> System.out.println("Initial free memory: " + mem1);<br /> r.gc();<br /> mem1 = r.freeMemory();<br /> System.out.println("Free memory after garbage collection: "<br /> + mem1);<br /> for(int i=0; i<1000; i++)<br /> someints[i] = new Integer(i); // allocate integers<br /> mem2 = r.freeMemory();<br /> System.out.println("Free memory after allocation: "<br /> + mem2);</div> <div>910 Java™ 2: The Complete Reference<br /> PropertyDescriptor, and EventSetDescriptor classes and the BeanInfo interface. It lists<br /> the properties and events of the Colors Bean that was developed earlier in this chapter.<br /> // Show properties and events.<br /> package sunw.demo.colors;<br /> import java.awt.*;<br /> import java.beans.*;<br /> public class IntrospectorDemo {<br /> public static void main(String args[]) {<br /> try {<br /> Class c = Class.forName("sunw.demo.colors.Colors");<br /> BeanInfo beanInfo = Introspector.getBeanInfo(c);<br /> BeanDescriptor beanDescriptor = beanInfo.getBeanDescriptor();<br /> System.out.println("Bean name = " +<br /> beanDescriptor.getName());<br /> System.out.println("Properties:");<br /> PropertyDescriptor propertyDescriptor[] =<br /> beanInfo.getPropertyDescriptors();<br /> for(int i = 0; i < propertyDescriptor.length; i++) {<br /> System.out.println("\t" + propertyDescriptor[i].getName());<br /> }<br /> }<br /> }<br /> System.out.println("Events:");<br /> EventSetDescriptor eventSetDescriptor[] =<br /> beanInfo.getEventSetDescriptors();<br /> for(int i = 0; i < eventSetDescriptor.length; i++) {<br /> System.out.println("\t" + eventSetDescriptor[i].getName());<br /> }<br /> }<br /> catch(Exception e) {<br /> System.out.println("Exception caught. " + e);<br /> }<br /> The output from this program is the following:<br /> Bean name = Colors<br /> Properties:</div> <div>972 Java™ 2: The Complete Reference<br /> is defined in ColorGet.htm and a servlet is defined in ColorGetServlet.java. The HTML<br /> source code for ColorGet.htm is shown in the following listing. It defines a form that<br /> contains a select element and a submit button. Notice that the action parameter of the<br /> form tag specifies a URL. The URL identifies a servlet to process the HTTP GET request.<br /> <html><br /> <body><br /> <center><br /> <form name="Form1"<br /> action="http://localhost:8080/examples/servlet/ColorGetServlet"><br /> <B>Color:</B><br /> <select name="color" size="1"><br /> <option value="Red">Red</option><br /> <option value="Green">Green</option><br /> <option value="Blue">Blue</option><br /> </select><br /> <br><br><br /> <input type=submit value="Submit"><br /> </form><br /> </body><br /> </html><br /> The source code for ColorGetServlet.java is shown in the following listing. The<br /> doGet( ) method is overridden to process any HTTP GET requests that are sent to<br /> this servlet. It uses the getParameter( ) method of HttpServletRequest to obtain the<br /> selection that was made by the user. A response is then formulated.<br /> import java.io.*;<br /> import javax.servlet.*;<br /> import javax.servlet.http.*;<br /> public class ColorGetServlet extends HttpServlet {<br /> public void doGet(HttpServletRequest request,<br /> HttpServletResponse response)<br /> throws ServletException, IOException {<br /> String color = request.getParameter("color");<br /> response.setContentType("text/html");<br /> PrintWriter pw = response.getWriter();<br /> pw.println("<B>The selected color is: ");<br /> pw.println(color);</div> <div>Chapter 8<br /> Inheritance<br /> 189</div> <div>Chapter 12<br /> I/O, Applets, and<br /> Other Topics<br /> 313</div> <div>400 Java™ 2: The Complete Reference<br /> Method<br /> static boolean isTitleCase(char ch)<br /> static boolean isUnicodeIdentifierPart(char ch)<br /> Description<br /> Returns true if ch is a Unicode<br /> titlecase character. Otherwise,<br /> it returns false.<br /> Returns true if ch is allowed as<br /> part of a Unicode identifier (other<br /> than the first character).<br /> Otherwise, it returns false.<br /> static boolean isUnicodeIdentifierStart(char ch) Returns true if ch is allowed<br /> as the first character of a Unicode<br /> identifier. Otherwise,<br /> it returns false.<br /> static boolean isUpperCase(char ch)<br /> static boolean isWhitespace(char ch)<br /> static char toLowerCase(char ch)<br /> static char toTitleCase(char ch)<br /> static char toUpperCase(char ch)<br /> Returns true if ch is an uppercase<br /> letter. Otherwise, it returns false.<br /> Returns true if ch is whitespace.<br /> Otherwise, it returns false.<br /> Returns lowercase equivalent of ch.<br /> Returns titlecase equivalent of ch.<br /> Returns uppercase equivalent of ch.<br /> Table 14-7.<br /> Various Character Methods (continued)<br /> Character defines the forDigit( ) and digit( ) methods, shown here:<br /> static char forDigit(int num, int radix)<br /> static int digit(char digit, int radix)<br /> forDigit( ) returns the digit character associated with the value of num. The radix of the<br /> conversion is specified by radix. digit( ) returns the integer value associated with the<br /> specified character (which is presumably a digit) according to the specified radix.<br /> Another method defined by Character is compareTo( ), which has the following<br /> two forms:<br /> int compareTo(Character c)<br /> int compareTo(Object obj)<br /> The first form returns 0 if the invoking object and c have the same value. It returns a<br /> negative value if the invoking object has a lower value. Otherwise, it returns a positive<br /> value. The second form works just like the first if obj is a reference to a Character.<br /> Otherwise, a ClassCastException is thrown. These methods were added by Java 2.</div> <div>366 Java™ 2: The Complete Reference<br /> str = br.readLine();<br /> str = str.trim(); // remove whitespace<br /> }<br /> }<br /> if(str.equals("Illinois"))<br /> System.out.println("Capital is Springfield.");<br /> else if(str.equals("Missouri"))<br /> System.out.println("Capital is Jefferson City.");<br /> else if(str.equals("California"))<br /> System.out.println("Capital is Sacramento.");<br /> else if(str.equals("Washington"))<br /> System.out.println("Capital is Olympia.");<br /> // ...<br /> } while(!str.equals("stop"));<br /> Data Conversion Using valueOf( )<br /> The valueOf( ) method converts data from its internal format into a human-readable<br /> form. It is a static method that is overloaded within String for all of Java’s built-in types,<br /> so that each type can be converted properly into a string. valueOf( ) is also overloaded<br /> for type Object,soanobject of any class type you create can also be used as an argument.<br /> (Recall that Object is a superclass for all classes.) Here are a few of its forms:<br /> static String valueOf(double num)<br /> static String valueOf(long num)<br /> static String valueOf(Object ob)<br /> static String valueOf(char chars[ ])<br /> As we discussed earlier, valueOf( ) is called when a string representation of some<br /> other type of data is needed—for example, during concatenation operations. You can call<br /> this method directly with any data type and get a reasonable String representation. All<br /> of the simple types are converted to their common String representation. Any object that<br /> you pass to valueOf( ) will return the result of a call to the object’s toString( ) method. In<br /> fact, you could just call toString( ) directly and get the same result.<br /> For most arrays, valueOf( ) returns a rather cryptic string, which indicates that it<br /> is an array of some type. For arrays of char, however, a String object is created that<br /> contains the characters in the char array. There is a special version of valueOf( ) that<br /> allows you to specify a subset of a char array. It has this general form:<br /> static String valueOf(char chars[ ], int startIndex, int numChars)</div> <div>290 Java™ 2: The Complete Reference<br /> You can obtain the current priority setting by calling the getPriority( ) method of<br /> Thread, shown here:<br /> final int getPriority( )<br /> Implementations of Java may have radically different behavior when it comes to<br /> scheduling. The Windows XP/98/NT/2000 version works, more or less, as you would<br /> expect. However, other versions may work quite differently. Most of the inconsistencies<br /> arise when you have threads that are relying on preemptive behavior, instead of<br /> cooperatively giving up CPU time. The safest way to obtain predictable, cross-platform<br /> behavior with Java is to use threads that voluntarily give up control of the CPU.<br /> The following example demonstrates two threads at different priorities, which do<br /> not run on a preemptive platform in the same way as they run on a nonpreemptive<br /> platform. One thread is set two levels above the normal priority, as defined by<br /> Thread.NORM_PRIORITY, and the other is set to two levels below it. The threads<br /> are started and allowed to run for ten seconds. Each thread executes a loop, counting<br /> the number of iterations. After ten seconds, the main thread stops both threads. The<br /> number of times that each thread made it through the loop is then displayed.<br /> // Demonstrate thread priorities.<br /> class clicker implements Runnable {<br /> int click = 0;<br /> Thread t;<br /> private volatile boolean running = true;<br /> }<br /> public clicker(int p) {<br /> t = new Thread(this);<br /> t.setPriority(p);<br /> }<br /> public void run() {<br /> while (running) {<br /> click++;<br /> }<br /> }<br /> public void stop() {<br /> running = false;<br /> }<br /> public void start() {<br /> t.start();<br /> }</div> <div>530 Java™ 2: The Complete Reference<br /> More than one object can be an observer. For example, the following program<br /> implements two observing classes and adds an object of each class to the<br /> BeingWatched observer list. The second observer waits until the count reaches<br /> zero and then rings the bell.<br /> /* An object may be observed by two or more<br /> observers.<br /> */<br /> import java.util.*;<br /> // This is the first observing class.<br /> class Watcher1 implements Observer {<br /> public void update(Observable obj, Object arg) {<br /> System.out.println("update() called, count is " +<br /> ((Integer)arg).intValue());<br /> }<br /> }<br /> // This is the second observing class.<br /> class Watcher2 implements Observer {<br /> public void update(Observable obj, Object arg) {<br /> // Ring bell when done<br /> if(((Integer)arg).intValue() == 0)<br /> System.out.println("Done" + '\7');<br /> }<br /> }<br /> // This is the class being observed.<br /> class BeingWatched extends Observable {<br /> void counter(int period) {<br /> for( ; period >=0; period--) {<br /> setChanged();<br /> notifyObservers(new Integer(period));<br /> try {<br /> Thread.sleep(100);<br /> } catch(InterruptedException e) {<br /> System.out.println("Sleep interrupted");<br /> }<br /> }<br /> }<br /> }</div> <div>THE JAVA LIBRARY<br /> Chapter 23: Images 809<br /> Canvas c = new Canvas();<br /> Image test = c.createImage(200, 100);<br /> Graphics gc = test.getGraphics();<br /> gc.setColor(Color.red);<br /> gc.fillRect(0, 0, 200, 100);<br /> Once you have constructed and filled an offscreen image, it will still not be visible.<br /> To actually display the image, call drawImage( ). Here is an example that draws a<br /> time-consuming image, to demonstrate the difference that double buffering can make<br /> in perceived drawing time:<br /> /*<br /> * <applet code=DoubleBuffer width=250 height=250><br /> * </applet><br /> */<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import java.applet.*;<br /> public class DoubleBuffer extends Applet {<br /> int gap = 3;<br /> int mx, my;<br /> boolean flicker = true;<br /> Image buffer = null;<br /> int w, h;<br /> public void init() {<br /> Dimension d = getSize();<br /> w = d.width;<br /> h = d.height;<br /> buffer = createImage(w, h);<br /> addMouseMotionListener(new MouseMotionAdapter() {<br /> public void mouseDragged(MouseEvent me) {<br /> mx = me.getX();<br /> my = me.getY();<br /> flicker = false;<br /> repaint();<br /> }<br /> public void mouseMoved(MouseEvent me) {<br /> mx = me.getX();<br /> my = me.getY();<br /> flicker = true;</div> <div>Appendix A<br /> Using Java’s<br /> Documentation<br /> Comments<br /> 1133</div> <div>692 Java™ 2: The Complete Reference<br /> Figure 21-1.<br /> The class hierarchy for Panel and Frame<br /> Container<br /> The Container class is a subclass of Component. It has additional methods that allow<br /> other Component objects to be nested within it. Other Container objects can be stored<br /> inside of a Container (since they are themselves instances of Component). This makes<br /> for a multileveled containment system. A container is responsible for laying out (that<br /> is, positioning) any components that it contains. It does this through the use of various<br /> layout managers, which you will learn about in Chapter 22.<br /> Panel<br /> The Panel class is a concrete subclass of Container. It doesn’t add any new methods; it<br /> simply implements Container. A Panel may be thought of as a recursively nestable,<br /> concrete screen component. Panel is the superclass for Applet. When screen output is<br /> directed to an applet, it is drawn on the surface of a Panel object. In essence, a Panel is<br /> a window that does not contain a title bar, menu bar, or border. This is why you don’t<br /> see these items when an applet is run inside a browser. When you run an applet using<br /> an applet viewer, the applet viewer provides the title and border.<br /> Other components can be added to a Panel object by its add( ) method (inherited<br /> from Container). Once these components have been added, you can position and resize<br /> them manually using the setLocation( ), setSize( ), or setBounds( ) methods defined by<br /> Component.</div> <div>1034 Java™ 2: The Complete Reference<br /> init( )<br /> The init( ) method for this transition starts like all other transitions, with a call to the<br /> base class’ init( ) method. It follows this with a call to the method described earlier,<br /> setupFillPixels( ). The initial values of the drop_amount and location variables are then<br /> calculated. After this, the init( ) method goes into a loop to create each frame. It actually<br /> does this in reverse, creating the last frame first. It does not have to be done in reverse.<br /> However, running loops in reverse saves one byte of code in the resulting class file. After<br /> each cell is created, the location variable is incremented to the next proper location.<br /> Smash( )<br /> The Smash( ) method modifies the work_pixels array for the next cell. It creates the<br /> smashed image of the old billboard in the work_pixels array and draws in the pixels<br /> for the new image. This method takes one parameter, max_fold, which is used as the<br /> maximum right offset that the lines in the fold will have. It is also used by subtracting<br /> this from the line width to determine the length of the lines to draw for the folds.<br /> The method begins by copying the pixels from the new image onto work_ pixels.<br /> It then initializes a number of variables that it uses to draw the smashed image. The<br /> drawing of this smashed image is done line by line, in a loop. Within the loop, it first<br /> makes the current line totally white. It then copies a portion of the correct line from<br /> the old billboard over this line. To get the accordion effect, it does not start drawing<br /> onto the same pixel location as it did for drawing the white line. It instead offsets<br /> the destination pixels to the right by a few pixels. After drawing in the line, it adds a<br /> number to the offset counter. It follows this with a bounds check to see if the offset has<br /> gone beyond the minimum or maximum offset. If it has, it flips the sign of the number<br /> it adds to the offset counter each line. The effect of this is that the direction of the offset<br /> is reversed.<br /> The Code<br /> Here is the source code for the SmashTransition class:<br /> import java.awt.*;<br /> import java.awt.image.*;<br /> public class SmashTransition extends BillTransition {<br /> final static int CELLS = 8;<br /> final static float FOLDS = 8.0f;<br /> static int[] fill_pixels;<br /> static void setupFillPixels(int width) {<br /> if(fill_pixels != null && fill_pixels.length <= width) {<br /> return;</div> <div>THE JAVA LANGUAGE<br /> Chapter 4: Operators 89<br /> }<br /> }<br /> System.out.println(" b = 0x"<br /> + hex[(b >> 4) & 0x0f] + hex[b & 0x0f]);<br /> System.out.println(" b >> 4 = 0x"<br /> + hex[(c >> 4) & 0x0f] + hex[c & 0x0f]);<br /> System.out.println(" b >>> 4 = 0x"<br /> + hex[(d >> 4) & 0x0f] + hex[d & 0x0f]);<br /> System.out.println("(b & 0xff) >> 4 = 0x"<br /> + hex[(e >> 4) & 0x0f] + hex[e & 0x0f]);<br /> The following output of this program shows how the >>> operator appears to do<br /> nothing when dealing with bytes. The variable b is set to an arbitrary negative byte<br /> value for this demonstration. Then c is assigned the byte value of b shifted right by<br /> four, which is 0xff because of the expected sign extension. Then d is assigned the byte<br /> value of b unsigned shifted right by four, which you might have expected to be 0x0f,<br /> but is actually 0xff because of the sign extension that happened when b was promoted<br /> to int before the shift. The last expression sets e to the byte value of b masked to 8 bits<br /> using the AND operator, then shifted right by four, which produces the expected value<br /> of 0x0f. Notice that the unsigned shift right operator was not used for d, since the state<br /> of the sign bit after the AND was known.<br /> b = 0xf1<br /> b >> 4 = 0xff<br /> b >>> 4 = 0xff<br /> (b & 0xff) >> 4 = 0x0f<br /> Bitwise Operator Assignments<br /> All of the binary bitwise operators have a shorthand form similar to that of the algebraic<br /> operators, which combines the assignment with the bitwise operation. For example, the<br /> following two statements, which shift the value in a right by four bits, are equivalent:<br /> a = a >> 4;<br /> a >>= 4;<br /> Likewise, the following two statements, which result in a being assigned the<br /> bitwise expression a OR b, are equivalent:<br /> a = a | b;<br /> a |= b;</div> <div>1152 Java™ 2: The Complete Reference<br /> Security problem, 10–11, 1070–1071<br /> and native methods, 340<br /> and servlets, 950–951, 979<br /> SecurityException, 266, 403, 408<br /> SecurityManager class, 434<br /> seek( ), 561<br /> select( ), 748, 752, 759<br /> Selection statements, 100–108<br /> Selectors, 851<br /> Semaphore, 292<br /> SequenceInputStream class, 316,<br /> 559–560<br /> Serializable interface, 577<br /> Serialization, 577–585<br /> example program, 583–585<br /> and static variables, 577<br /> and transient variables, 577<br /> Server, 589<br /> proxy, 590<br /> ServerSocket class, 595, 601–602<br /> service( ), 951, 953, 955, 956<br /> Servlet(s), 950–979<br /> advantages of, 950–951<br /> example of simple, 953–954<br /> life cycle of, 951<br /> parameters, reading,<br /> 960–962<br /> and security, 950–951, 979<br /> and session tracking,<br /> 977–979<br /> using Tomcat to develop,<br /> 951–952<br /> Servlet interface, 955–956<br /> methods, table of, 956<br /> ServletConfig interface, 955, 956<br /> ServletContext interface, 955–957<br /> methods, table of, 957<br /> ServletException class, 955, 960<br /> ServletInputStream class, 955, 960<br /> ServletOutputStream class,<br /> 955, 960<br /> ServletRequest interface, 953, 955,<br /> 957, 960<br /> methods, table of, 958–959<br /> ServletResponse interface, 953,<br /> 955, 957<br /> methods, table of, 959<br /> Session tracking, 977–979<br /> Set interface, 442, 447<br /> Set-view, obtaining, 497<br /> set( ), 445, 446, 454<br /> setAlignment( ), 738<br /> setAttribute( ), 967, 978<br /> setBackground( ), 636, 713<br /> setBlockIncrement( ), 755<br /> setBounds( ), 692, 764<br /> setChanged( ), 527<br /> setCharAt( ), 371<br /> setColor( ), 714<br /> setContentType( ), 953<br /> setDefault( ), 524<br /> setEchoCharacter( ), 759<br /> setEditable( ), 759<br /> setEnabled( ), 776<br /> setFont( ), 720<br /> setForeground( ), 636, 713<br /> SetIntField( ), 339<br /> setLabel( ), 739, 743, 776<br /> setLastModified( ), 542<br /> setLayout( ), 763–764<br /> setLength( ), 370–371, 562<br /> setLocation( ), 692<br /> setMaxAge( ), 969, 977<br /> setN( ), 894, 895, 896<br /> setName( ), 278, 279<br /> setPaintMode( ), 715<br /> setPriority( ), 289<br /> setReadOnly( ), 542<br /> setSelectedCheckbox( ), 746<br /> setSize( ), 692, 694, 695<br /> setState( ), 743, 777<br /> setText( ), 738, 758<br /> setTitle( ), 704<br /> setUnitIncrement( ), 755<br /> setValue( ), 755<br /> setValues( ), 755<br /> setVisible( ), 694, 695<br /> setXORMode( ), 715<br /> Sheridan, Mike, 7<br /> Shift operators, bitwise, 80, 84–89<br /> Short class, 387, 396, 397<br /> methods defined by, table<br /> of, 389–390<br /> short data type, 42, 43, 44, 50<br /> show( ), 772, 773<br /> showDocument( ), 649, 650–651,<br /> 1048, 1056<br /> showStatus( ), 642, 681<br /> shuffle( ), 477, 479<br /> Sign extension, 87<br /> SimpleBeanInfo class, 903, 909<br /> SimpleDateFormat class, 524,<br /> 880–882<br /> SimpleTimeZone class, 522–523<br /> sin( ), 420<br /> SingleThreadModel interface,<br /> 955, 957<br /> size( ), 444, 445, 455, 493, 851<br /> Skeletons (RMI), 876–877<br /> skip( ), 548, 556, 558<br /> sleep( ), 277, 278, 279<br /> slice( ), 850<br /> Socket(s)<br /> example program of<br /> client/server, 602–623<br /> overview, 588–589<br /> reserved, 589–590<br /> TCP/IP client, 594–597<br /> TCP/IP server, 601<br /> Socket class, 595–596<br /> SocketChannel class, 850<br /> sort( ), 482<br /> SortedMap interface, 465<br /> methods, table of, 465<br /> SortedSet interface, 442, 447–448<br /> methods, table of, 447–448<br /> Source code, 25–26<br /> split( ), 368, 867–868<br /> sqrt( ), 53, 421<br /> Stack, definition of, 152<br /> Stack class, 490–492<br /> methods, table of, 491<br /> Stack trace, 252, 435<br /> StackTraceElement class, 435<br /> methods, table of, 435<br /> Standard Template Library (STL),<br /> 442<br /> start( ), 277, 280, 282, 632, 634, 637,<br /> 860, 864<br /> startsWith( ), 358–359<br /> Statements, 29<br /> null, 110<br /> Statements, control<br /> iteration, 100, 109–119<br /> jump, 100, 119–127<br /> selection, 100–108<br /> static, 28, 176–178<br /> stop( ), 15, 308, 632, 634, 635, 651<br /> store( ), 498, 499, 502–504<br /> Stream(s)<br /> benefits, 585<br /> buffered, 555–559<br /> classes, byte, 315, 316,<br /> 545–562<br /> classes, character, 315, 317,<br /> 545, 562–577<br /> definition of, 314, 538<br /> filtered, 555<br /> predefined, 318<br /> StreamTokenizer class, 574–577<br /> strictfp, 39, 335<br /> StrictMath class, 422<br /> String(s)<br /> arrays of, 187, 188<br /> changing case of characters<br /> in, 367<br /> comparison, 356–361</div> <div>4 Java™ 2: The Complete Reference<br /> When the chronicle of computer languages is written, the following will be said:<br /> B led to C, C evolved into C++, and C++ set the stage for Java. To understand<br /> Java is to understand the reasons that drove its creation, the forces that<br /> shaped it, and the legacy that it inherits. Like the successful computer languages that<br /> came before, Java is a blend of the best elements of its rich heritage combined with the<br /> innovative concepts required by its unique environment. While the remaining chapters<br /> of this book describe the practical aspects of Java—including its syntax, libraries, and<br /> applications—in this chapter, you will learn how and why Java came about, and what<br /> makes it so important.<br /> Although Java has become inseparably linked with the online environment of the<br /> Internet, it is important to remember that Java is first and foremost a programming<br /> language. Computer language innovation and development occurs for two fundamental<br /> reasons:<br /> ■ To adapt to changing environments and uses<br /> ■ To implement refinements and improvements in the art of programming<br /> As you will see, the creation of Java was driven by both elements in nearly<br /> equal measure.<br /> Java’s Lineage<br /> Java is related to C++, which is a direct descendent of C. Much of the character of Java<br /> is inherited from these two languages. From C, Java derives its syntax. Many of Java’s<br /> object-oriented features were influenced by C++. In fact, several of Java’s defining<br /> characteristics come from—or are responses to—its predecessors. Moreover, the creation<br /> of Java was deeply rooted in the process of refinement and adaptation that has been<br /> occurring in computer programming languages for the past three decades. For these<br /> reasons, this section reviews the sequence of events and forces that led up to Java. As<br /> you will see, each innovation in language design was driven by the need to solve a<br /> fundamental problem that the preceding languages could not solve. Java is no exception.<br /> The Birth of Modern Programming: C<br /> The C language shook the computer world. Its impact should not be underestimated,<br /> because it fundamentally changed the way programming was approached and thought<br /> about. The creation of C was a direct result of the need for a structured, efficient, highlevel<br /> language that could replace assembly code when creating systems programs. As<br /> you probably know, when a computer language is designed, trade-offs are often made,<br /> such as the following:<br /> ■ Ease-of-use versus power<br /> ■ Safety versus efficiency<br /> ■ Rigidity versus extensibility</div> <div>364 Java™ 2: The Complete Reference<br /> i = org.indexOf(search);<br /> if(i != -1) {<br /> result = org.substring(0, i);<br /> result = result + sub;<br /> result = result + org.substring(i + search.length());<br /> org = result;<br /> }<br /> } while(i != -1);<br /> }<br /> }<br /> The output from this program is shown here:<br /> This is a test. This is, too.<br /> Thwas is a test. This is, too.<br /> Thwas was a test. This is, too.<br /> Thwas was a test. Thwas is, too.<br /> Thwas was a test. Thwas was, too.<br /> concat( )<br /> You can concatenate two strings using concat( ), shown here:<br /> String concat(String str)<br /> This method creates a new object that contains the invoking string with the contents<br /> of str appended to the end. concat( ) performs the same function as +. For example,<br /> String s1 = "one";<br /> String s2 = s1.concat("two");<br /> puts the string “onetwo” into s2. It generates the same result as the following sequence:<br /> String s1 = "one";<br /> String s2 = s1 + "two";<br /> replace( )<br /> The replace( ) method replaces all occurrences of one character in the invoking string<br /> with another character. It has the following general form:</div> <div>158 Java™ 2: The Complete Reference<br /> }<br /> System.out.println("No parameters");<br /> }<br /> // Overload test for two integer parameters.<br /> void test(int a, int b) {<br /> System.out.println("a and b: " + a + " " + b);<br /> }<br /> // overload test for a double parameter<br /> void test(double a) {<br /> System.out.println("Inside test(double) a: " + a);<br /> }<br /> class Overload {<br /> public static void main(String args[]) {<br /> OverloadDemo ob = new OverloadDemo();<br /> int i = 88;<br /> ob.test();<br /> ob.test(10, 20);<br /> }<br /> }<br /> ob.test(i); // this will invoke test(double)<br /> ob.test(123.2); // this will invoke test(double)<br /> This program generates the following output:<br /> No parameters<br /> a and b: 10 20<br /> Inside test(double) a: 88<br /> Inside test(double) a: 123.2<br /> As you can see, this version of OverloadDemo does not define test(int). Therefore,<br /> when test( ) is called with an integer argument inside Overload, no matching method<br /> is found. However, Java can automatically convert an integer into a double, and this<br /> conversion can be used to resolve the call. Therefore, after test(int) is not found, Java<br /> elevates i to double and then calls test(double). Of course, if test(int) had been defined,</div> <div>590 Java™ 2: The Complete Reference<br /> Here’s an example of a client requesting a single file, /index.html, and the server<br /> replying that it has successfully found the file and is sending it to the client:<br /> Server<br /> Client<br /> Listens to port 80. Connects to port 80.<br /> Accepts the connection.<br /> Writes “GET /index.html<br /> HTTP/1.0\n\n”.<br /> Reads up until the second end-of-line (\n).<br /> Sees that GET is a known command and that<br /> HTTP/1.0 is a valid protocol version.<br /> Reads a local file called /index.html.<br /> Writes “HTTP/1.0 200 OK\n\n”.<br /> “200” means “here comes the file.”<br /> Copies the contents of the file into the socket. Reads the contents of the file and<br /> displays it.<br /> Hangs up.<br /> Hangs up.<br /> Obviously, the HTTP protocol is much more complicated than this example shows,<br /> but this is an actual transaction that you could have with any web server near you.<br /> Proxy Servers<br /> A proxy server speaks the client side of a protocol to another server. This is often<br /> required when clients have certain restrictions on which servers they can connect to.<br /> Thus, a client would connect to a proxy server, which did not have such restrictions,<br /> and the proxy server would in turn communicate for the client. A proxy server has<br /> the additional ability to filter certain requests or cache the results of those requests for<br /> future use. A caching proxy HTTP server can help reduce the bandwidth demands on<br /> a local network’s connection to the Internet. When a popular web site is being hit by<br /> hundreds of users, a proxy server can get the contents of the web server’s popular<br /> pages once, saving expensive internetwork transfers while providing faster access to<br /> those pages to the clients.<br /> Later in this chapter, we will actually build a complete caching proxy HTTP server.<br /> The interesting part about this sample program is that it is both a client and a server.<br /> To serve certain pages, it must act as a client to other servers to obtain a copy of the<br /> requested content.<br /> Internet Addressing<br /> Every computer on the Internet has an address. An Internet address is a number that<br /> uniquely identifies each computer on the Net. Originally, all Internet addresses</div> <div>THE JAVA LANGUAGE<br /> Chapter 2: An Overview of Java 23<br /> Figure 2-2.<br /> Labrador inherits the encapsulation of all of its superclasses</div> <div>Chapter 3<br /> Data Types, Variables,<br /> and Arrays<br /> 41</div> <div>THE JAVA LIBRARY<br /> Chapter 13: String Handling 359<br /> "Foobar".startsWith("bar", 3)<br /> returns true.<br /> equals( ) Versus ==<br /> It is important to understand that the equals( ) method and the == operator perform<br /> two different operations. As just explained, the equals( ) method compares the<br /> characters inside a String object. The == operator compares two object references to<br /> see whether they refer to the same instance. The following program shows how two<br /> different String objects can contain the same characters, but references to these objects<br /> will not compare as equal:<br /> // equals() vs ==<br /> class EqualsNotEqualTo {<br /> public static void main(String args[]) {<br /> String s1 = "Hello";<br /> String s2 = new String(s1);<br /> }<br /> }<br /> System.out.println(s1 + " equals " + s2 + " -> " +<br /> s1.equals(s2));<br /> System.out.println(s1 + " == " + s2 + " -> " + (s1 == s2));<br /> The variable s1 refers to the String instance created by “Hello”. The object<br /> referred to by s2 is created with s1 as an initializer. Thus, the contents of the two<br /> String objects are identical, but they are distinct objects. This means that s1 and s2<br /> do not refer to the same objects and are, therefore, not ==, asisshown here by the<br /> output of the preceding example:<br /> Hello equals Hello -> true<br /> Hello == Hello -> false<br /> compareTo( )<br /> Often, it is not enough to simply know whether two strings are identical. For sorting<br /> applications, you need to know which is less than, equal to, or greater than the next. A<br /> string is less than another if it comes before the other in dictionary order. A string is<br /> greater than another if it comes after the other in dictionary order. The String method<br /> compareTo( ) serves this purpose. It has this general form:<br /> int compareTo(String str)</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 27: Servlets 969<br /> Method<br /> Description<br /> void setComment(String c) Sets the comment to c.<br /> void setDomain(String d) Sets the domain to d.<br /> void setMaxAge(int secs)<br /> void setPath(String p) Sets the path to p.<br /> void setSecure(boolean secure)<br /> void setValue(String v) Sets the value to v.<br /> void setVersion(int v)<br /> Sets the maximum age of the cookie to secs.<br /> This is the number of seconds after which the<br /> cookie is deleted. Passing –1 causes the cookie<br /> to be removed when the browser is terminated.<br /> Sets the security flag to secure, which means<br /> that cookies will be sent only when a secure<br /> protocol is being used.<br /> Sets the cookie protocol version to v, which will<br /> be 0 or 1.<br /> Table 27-8.<br /> The Methods Defined by Cookie (continued)<br /> The HttpServlet Class<br /> The HttpServlet class extends GenericServlet. It is commonly used when developing<br /> servlets that receive and process HTTP requests. The methods of the HttpServlet class<br /> are summarized in Table 27-9.<br /> Method<br /> void doDelete(HttpServletRequest req,<br /> HttpServletResponse res)<br /> throws IOException, ServletException<br /> void doGet(HttpServletRequest req,<br /> HttpServletResponse res)<br /> throws IOException, ServletException<br /> Description<br /> Performs an HTTP DELETE.<br /> Performs an HTTP GET.<br /> Table 27-9.<br /> The Methods Defined by HttpServlet</div> <div>430 Java™ 2: The Complete Reference<br /> }<br /> }<br /> class ThreadGroupDemo {<br /> public static void main(String args[]) {<br /> ThreadGroup groupA = new ThreadGroup("Group A");<br /> ThreadGroup groupB = new ThreadGroup("Group B");<br /> NewThread ob1 = new NewThread("One", groupA);<br /> NewThread ob2 = new NewThread("Two", groupA);<br /> NewThread ob3 = new NewThread("Three", groupB);<br /> NewThread ob4 = new NewThread("Four", groupB);<br /> System.out.println("\nHere is output from list():");<br /> groupA.list();<br /> groupB.list();<br /> System.out.println();<br /> System.out.println("Suspending Group A");<br /> Thread tga[] = new Thread[groupA.activeCount()];<br /> groupA.enumerate(tga); // get threads in group<br /> for(int i = 0; i < tga.length; i++) {<br /> ((NewThread)tga[i]).mysuspend(); // suspend each thread<br /> }<br /> try {<br /> Thread.sleep(4000);<br /> } catch (InterruptedException e) {<br /> System.out.println("Main thread interrupted.");<br /> }<br /> System.out.println("Resuming Group A");<br /> for(int i = 0; i < tga.length; i++) {<br /> ((NewThread)tga[i]).myresume(); // resume threads in group<br /> }<br /> // wait for threads to finish<br /> try {<br /> System.out.println("Waiting for threads to finish.");<br /> ob1.join();<br /> ob2.join();<br /> ob3.join();</div> <div>162 Java™ 2: The Complete Reference<br /> }<br /> }<br /> // get volume of cube<br /> vol = mycube.volume();<br /> System.out.println("Volume of mycube is " + vol);<br /> The output produced by this program is shown here:<br /> Volume of mybox1 is 3000.0<br /> Volume of mybox2 is -1.0<br /> Volume of mycube is 343.0<br /> As you can see, the proper overloaded constructor is called based upon the parameters<br /> specified when new is executed.<br /> Using Objects as Parameters<br /> So far we have only been using simple types as parameters to methods. However, it is<br /> both correct and common to pass objects to methods. For example, consider the following<br /> short program:<br /> // Objects may be passed to methods.<br /> class Test {<br /> int a, b;<br /> }<br /> Test(int i, int j) {<br /> a = i;<br /> b = j;<br /> }<br /> // return true if o is equal to the invoking object<br /> boolean equals(Test o) {<br /> if(o.a == a && o.b == b) return true;<br /> else return false;<br /> }<br /> class PassOb {<br /> public static void main(String args[]) {</div> <div>58 Java™ 2: The Complete Reference<br /> than the range of a byte, it will be reduced modulo (the remainder of an integer<br /> division by the) byte’s range.<br /> int a;<br /> byte b;<br /> // ...<br /> b = (byte) a;<br /> A different type of conversion will occur when a floating-point value is assigned to<br /> an integer type: truncation. As you know, integers do not have fractional components.<br /> Thus, when a floating-point value is assigned to an integer type, the fractional component<br /> is lost. For example, if the value 1.23 is assigned to an integer, the resulting value will<br /> simply be 1. The 0.23 will have been truncated. Of course, if the size of the whole number<br /> component is too large to fit into the target integer type, then that value will be reduced<br /> modulo the target type’s range.<br /> The following program demonstrates some type conversions that require casts:<br /> // Demonstrate casts.<br /> class Conversion {<br /> public static void main(String args[]) {<br /> byte b;<br /> int i = 257;<br /> double d = 323.142;<br /> System.out.println("\nConversion of int to byte.");<br /> b = (byte) i;<br /> System.out.println("i and b " + i + " " + b);<br /> System.out.println("\nConversion of double to int.");<br /> i = (int) d;<br /> System.out.println("d and i " + d + " " + i);<br /> }<br /> }<br /> System.out.println("\nConversion of double to byte.");<br /> b = (byte) d;<br /> System.out.println("d and b " + d + " " + b);<br /> This program generates the following output:</div> <div>Index<br /> & (bitwise AND), 80, 82<br /> & (Boolean logical AND), 92, 94<br /> && (short-circuit AND), 92<br /> * (multiplication), 31, 74<br /> * (regular expression quantifier),<br /> 861<br /> * (used in import statement), 233<br /> @ tags (javadoc), 1134–1138<br /> | (bitwise OR), 80, 82<br /> | (Boolean logical OR), 92<br /> || (short-circuit OR), 92<br /> [ ], 38, 861, 866<br /> ^ (bitwise exclusive OR), 80, 82, 83<br /> ^(Boolean logical exclusive OR), 92<br /> :, 123<br /> , (comma), 38, 116–117<br /> { }, 27, 28, 35, 38, 63, 254<br /> =, 31, 94–95<br /> = = (relational operator), 90, 91<br /> versus equals( ), 359<br /> = = (Boolean operator), 92<br /> !, 92<br /> !=, 90, 91, 92<br /> /, 74<br /> /* */, 27<br /> /** */, 38, 1134<br /> //, 27–28<br /> <, 91<br /> <<, 80, 84–86<br /> <=, 91<br /> –, 74<br /> – –, 35, 74, 78–80<br /> %, 74, 76<br /> ( ), 38, 96–98<br /> . (dot operator), 132, 140, 177–178<br /> . (regular expression wildcard<br /> character), 861, 865<br /> . (separator), 38, 232, 233<br /> + (addition), 74<br /> + (concatenation operator), 31, 185,<br /> 352–353, 372, 373<br /> + (regular expression quantifier),<br /> 861, 864–865<br /> ++, 34–35, 74, 78–80<br /> ? (regular expression quantifier),<br /> 861, 865–866<br /> ?:, 92, 95–96<br /> >, 90<br /> >>, 80, 86–87<br /> >>>, 80, 87–89<br /> >=, 91<br /> ; (semicolon), 29, 38, 110<br /> ~, 80, 82<br /> A<br /> abs( ), 159<br /> abstract type modifier, 216, 220<br /> Abstract Window Toolkit (AWT),<br /> 314, 329, 331, 628, 632, 688, 736<br /> and applet architecture,<br /> 631–632<br /> classes, table of, 688–691<br /> components, extending,<br /> 790–797<br /> creating stand-alone<br /> windows with, 702–704<br /> AbstractButton class, 927<br /> AbstractCollection class, 448<br /> AbstractList class, 448<br /> AbstractMap class, 466, 467<br /> AbstractSequentialList class, 448<br /> AbstractSet class, 449<br /> accept( ), 543, 545, 602<br /> Access control, 172–176<br /> example program, 229–232<br /> and packages, 224, 227–228<br /> Access specifiers, 28, 172, 227–228<br /> Accessibility API, 948<br /> acos( ), 420<br /> ActionEvent class, 657, 658–659,<br /> 739, 752, 777<br /> ActionListener interface, 669, 670,<br /> 739, 752, 777<br /> actionPerformed( ), 670, 739<br /> Adapter classes, 680–682<br /> add( ), 443, 445, 446, 447, 454, 455,<br /> 692, 736–737, 748, 751, 767, 772,<br /> 777<br /> addAll( ), 443, 445, 446<br /> 1141</div> <div>Chapter 15<br /> java.util Part 1: The<br /> Collections Framework<br /> 439</div> <div>870 Java™ 2: The Complete Reference<br /> Class<br /> AccessibleObject<br /> Array<br /> Constructor<br /> Field<br /> Method<br /> Modifier<br /> Proxy<br /> ReflectPermission<br /> Primary Function<br /> Allows you to bypass the default access control checks.<br /> (Added by Java 2)<br /> Allows you to dynamically create and manipulate arrays.<br /> Provides information about a constructor.<br /> Provides information about a field.<br /> Provides information about a method.<br /> Provides information about class and member access<br /> modifiers.<br /> Supports dynamic proxy classes. (Added by Java 2, v1.3)<br /> Allows reflection of private or protected members of a class.<br /> (Added by Java 2)<br /> Table 24-4.<br /> Classes Defined in java.lang.reflect<br /> to obtain information about an object. You will want to explore these on your own.<br /> However, each supports the toString( ) method. Therefore, using Constructor, Field,<br /> and Method objects as arguments to the println( ) method is straightforward, as shown<br /> in the program.<br /> // Demonstrate reflection.<br /> import java.lang.reflect.*;<br /> public class ReflectionDemo1 {<br /> public static void main(String args[]) {<br /> try {<br /> Class c = Class.forName("java.awt.Dimension");<br /> System.out.println("Constructors:");<br /> Constructor constructors[] = c.getConstructors();<br /> for(int i = 0; i < constructors.length; i++) {<br /> System.out.println(" " + constructors[i]);<br /> }<br /> System.out.println("Fields:");<br /> Field fields[] = c.getFields();<br /> for(int i = 0; i < fields.length; i++) {<br /> System.out.println(" " + fields[i]);</div> <div>722 Java™ 2: The Complete Reference<br /> }<br /> }<br /> sampleFonts.f = new Font("SansSerif", Font.PLAIN, 12);<br /> sampleFonts.msg = "SansSerif";<br /> break;<br /> case 3:<br /> sampleFonts.f = new Font("Serif", Font.PLAIN, 12);<br /> sampleFonts.msg = "Serif";<br /> break;<br /> case 4:<br /> sampleFonts.f = new Font("Monospaced", Font.PLAIN, 12);<br /> sampleFonts.msg = "Monospaced";<br /> break;<br /> }<br /> if(sampleFonts.next == 4) sampleFonts.next = -1;<br /> sampleFonts.setFont(sampleFonts.f);<br /> sampleFonts.repaint();<br /> Sample output from this program is shown here:<br /> Obtaining Font Information<br /> Suppose you want to obtain information about the currently selected font. To do this,<br /> you must first get the current font by calling getFont( ). This method is defined by the<br /> Graphics class, as shown here:<br /> Font getFont( )<br /> Once you have obtained the currently selected font, you can retrieve information about<br /> it using various methods defined by Font. For example, this applet displays the name,<br /> family, size, and style of the currently selected font:</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 25: Java Beans 911<br /> Events:<br /> rectangular<br /> propertyChange<br /> component<br /> mouseMotion<br /> mouse<br /> hierarchy<br /> key<br /> focus<br /> hierarchyBounds<br /> inputMethod<br /> Using Bean Builder<br /> As explained at the start of the chapter, the BDK is not compatible with Java 2, version 1.4.<br /> Instead, 1.4 users will need to use the new Bean Builder tool for Bean development. At<br /> the time of this writing, Bean Builder is available only as a beta release, and its final<br /> form and feature set are subject to change. However, because it is the tool that Java 2,<br /> version 1.4 users must use to develop Beans, an overview of Bean Builder is presented<br /> here. (Subsequent editions of this book will cover Bean Builder in detail after it is a<br /> released product.) Keep in mind that the basic Bean information, such as introspection,<br /> described earlier, also applies to Beans used by Bean Builder. Bean Builder is available<br /> from http://java.sun.com.<br /> Bean Builder is similar to the BeanBox offered by the BDK, except that it is more<br /> powerful and sophisticated. Its operation is also similar to the BeanBox except that it is<br /> easier to use. Perhaps the most striking feature of Bean Builder is that it supports two<br /> separate modes of operation: design and test. In design mode, you construct a Bean-based<br /> application, adding the various components, and wiring them together. In test mode,<br /> also called run-time mode, the application is executed and all of the components are live.<br /> Thus, it is extremely easy to construct and then test your application. Futhermore, you<br /> switch between these two modes by checking or clearing a single check box.<br /> Bean Builder provides the three windows shown in Figure 25-6. The top (main)<br /> window holds the current palette set. This includes a default palette from which you<br /> can choose various user-interface objects, such as buttons, scroll bars, lists, and menus.<br /> These are Swing rather than AWT objects. (You will find an overview of Swing in<br /> Chapter 26, but no knowledge of Swing is required to follow along with the example<br /> developed later in this section.) You can also load other palettes and JAR files. Each<br /> component has associated with it a set of properties. You can examine and set these<br /> using the Property Inspector window provided by Bean Builder. The third window,</div> <div>524 Java™ 2: The Complete Reference<br /> ENGLISH JAPAN TRADITIONAL_CHINESE<br /> FRANCE JAPANESE UK<br /> FRENCH KOREA US<br /> For example, the expression Locale.CANADA represents the Locale object for Canada.<br /> The constructors for Locale are<br /> Locale(String language)<br /> Locale(String language, String country)<br /> Locale(String language, String country, String data)<br /> These constructors build a Locale object to represent a specific language and in the<br /> case of the last two, country. These values must contain ISO-standard language and<br /> country codes. Auxiliary browser and vendor-specific information can be provided in<br /> data. The first constructor was added by Java 2, version 1.4.<br /> Locale defines several methods. One of the most important is setDefault( ),<br /> shown here:<br /> static void setDefault(Locale localeObj)<br /> This sets the default locale to that specified by localeObj.<br /> Some other interesting methods are the following:<br /> final String getDisplayCountry( )<br /> final String getDisplayLanguage( )<br /> final String getDisplayName( )<br /> These return human-readable strings that can be used to display the name of the<br /> country, the name of the language, and the complete description of the locale.<br /> The default locale can be obtained using getDefault( ), shown here:<br /> static Locale getDefault( )<br /> Calendar and GregorianCalendar are examples of classes that operate in a localesensitive<br /> manner. DateFormat and SimpleDateFormat also depend on the locale.<br /> Random<br /> The Random class is a generator of pseudorandom numbers. These are called<br /> pseudorandom numbers because they are simply uniformly distributed sequences.<br /> Random defines the following constructors:<br /> Random( )<br /> Random(long seed)<br /> The first version creates a number generator that uses the current time as the starting,<br /> or seed, value. The second form allows you to specify a seed value manually.<br /> If you initialize a Random object with a seed, you define the starting point for the<br /> random sequence. If you use the same seed to initialize another Random object, you will</div> <div>APPLYING JAVA<br /> Chapter 32: Scrabblet: A Multiplayer Word Game 1085<br /> nameEntered( )<br /> The nameEntered( ) method is called from actionPerformed( ) whenever ENTER is<br /> pressed in the original prompt for the user’s name. Any AWT components that might<br /> be in the way are removed, and then a new List object, idList, is created to store the<br /> names of the other players. The method also adds a button at the top named challenge,<br /> then notifies the server that we are here by calling setName( ).<br /> private void nameEntered(String s) {<br /> if (s.equals(""))<br /> return;<br /> name = s;<br /> if (ican != null)<br /> remove(ican);<br /> if (idList != null)<br /> remove(idList);<br /> if (challenge != null)<br /> remove(challenge);<br /> idList = new List(10, false);<br /> add("Center", idList);<br /> challenge = new Button("Challenge");<br /> challenge.addActionListener(this);<br /> add("North", challenge);<br /> validate();<br /> server.setName(name);<br /> showStatus("Wait for other players to arrive.");<br /> if (topPanel != null)<br /> remove(topPanel);<br /> }<br /> wepick( ) and theypick( )<br /> The methods wepick( ) and theypick( ) are simply used to start off the game by<br /> picking the seven tiles for each player. It is important that the caller do these in the<br /> right order on each side of the challenge, depending on who goes first. The call to<br /> bag.takeOut( ) gets a single letter permanently out of the shared bag. The call to<br /> board.addLetter( ) places the tile on our tray. For the other side, theypick( ) simply<br /> saves the letters in theirs.<br /> private void wepick() {<br /> for (int i = 0; i < 7; i++) {</div> <div>92 Java™ 2: The Complete Reference<br /> Boolean Logical Operators<br /> The Boolean logical operators shown here operate only on boolean operands. All<br /> of the binary logical operators combine two boolean values to form a resultant<br /> boolean value.<br /> Operator<br /> &<br /> Result<br /> Logical AND<br /> | Logical OR<br /> ^<br /> Logical XOR (exclusive OR)<br /> || Short-circuit OR<br /> &&<br /> Short-circuit AND<br /> ! Logical unary NOT<br /> &=<br /> AND assignment<br /> |= OR assignment<br /> ^= XOR assignment<br /> == Equal to<br /> != Not equal to<br /> ?: Ternary if-then-else<br /> The logical Boolean operators, &, |, and ^, operate on boolean values in the same<br /> way that they operate on the bits of an integer. The logical ! operator inverts the<br /> Boolean state: !true == false and !false == true. The following table shows the effect<br /> of each logical operation:<br /> A B A | B A & B A ^ B !A<br /> False False False False False True<br /> True False True False True False<br /> False True True False True True<br /> True True True True False False<br /> Here is a program that is almost the same as the BitLogic example shown earlier,<br /> but it operates on boolean logical values instead of binary bits:</div> <div>APPLYING JAVA<br /> Chapter 31: The Lavatron Applet: A Sports Arena Display 1065<br /> IntHash( )<br /> As mentioned in the preceding section, Color objects are stored in a hash table rather<br /> than creating the same ones over and over. As a further optimization, we created our<br /> own version of Java’s Hashtable class, which uses normal ints as keys rather than<br /> requiring an Object handle.<br /> Integer data needs much less room to store in the pixel array than Color objects,<br /> so we use a hash table as a mechanism to look up Color objects from the integer value<br /> of any individual pixel. Creating Color objects on the fly from the integer value of<br /> each pixel is very expensive, because it creates a lot of memory garbage that must be<br /> collected. One possible solution would be to use a Java Hashtable, except that doing so<br /> would create just as much garbage, since only objects can be used as keys in a standard<br /> Java hash table. Thus, to store an int in Java’s hash table, you would have to create a<br /> new Integer object as a key to be matched. In a high duty cycle applet like Lavatron,<br /> garbage Integer objects would be created by the thousands per second. This is not a<br /> good solution.<br /> The proper solution was to build our own hash table, IntHash, which uses the<br /> integer data type values rather than the Integer object for its keys. IntHash is about 60<br /> lines of code. The IntHash class duplicates the interface of the java.util.Hashtable class<br /> with the exception that the type of the argument to put( ) and get( ) is an int data type<br /> rather than an Object. There’s no need to explain how a hash table works in this<br /> chapter, but suffice it to say that put(42, “Hello”) == get(42).<br /> The Code<br /> Here is the source code for the IntHash class:<br /> class IntHash {<br /> private int capacity;<br /> private int size;<br /> private float load = 0.7F;<br /> private int keys[];<br /> private Object vals[];<br /> public IntHash(int n) {<br /> capacity = n;<br /> size = 0;<br /> keys = new int[n];<br /> vals = new Object[n];<br /> }<br /> public IntHash() {<br /> this(101);</div> <div>640 Java™ 2: The Complete Reference<br /> */<br /> public class SimpleBanner extends Applet implements Runnable {<br /> String msg = " A Simple Moving Banner.";<br /> Thread t = null;<br /> int state;<br /> boolean stopFlag;<br /> // Set colors and initialize thread.<br /> public void init() {<br /> setBackground(Color.cyan);<br /> setForeground(Color.red);<br /> }<br /> // Start thread<br /> public void start() {<br /> t = new Thread(this);<br /> stopFlag = false;<br /> t.start();<br /> }<br /> // Entry point for the thread that runs the banner.<br /> public void run() {<br /> char ch;<br /> }<br /> // Display banner<br /> for( ; ; ) {<br /> try {<br /> repaint();<br /> Thread.sleep(250);<br /> ch = msg.charAt(0);<br /> msg = msg.substring(1, msg.length());<br /> msg += ch;<br /> if(stopFlag)<br /> break;<br /> } catch(InterruptedException e) {}<br /> }<br /> // Pause the banner.<br /> public void stop() {</div> <div>THE JAVA LIBRARY<br /> Chapter 20: Event Handling 669<br /> Event Listener Interfaces<br /> As explained, the delegation event model has two parts: sources and listeners. Listeners<br /> are created by implementing one or more of the interfaces defined by the java.awt.event<br /> package. When an event occurs, the event source invokes the appropriate method defined<br /> by the listener and provides an event object as its argument. Table 20-3 lists commonly<br /> used listener interfaces and provides a brief description of the methods that they define.<br /> The following sections examine the specific methods that are contained in each interface.<br /> Interface<br /> ActionListener<br /> AdjustmentListener<br /> ComponentListener<br /> ContainerListener<br /> FocusListener<br /> ItemListener<br /> KeyListener<br /> MouseListener<br /> MouseMotionListener<br /> MouseWheelListener<br /> TextListener<br /> WindowFocusListener<br /> WindowListener<br /> Description<br /> Defines one method to receive action events.<br /> Defines one method to receive adjustment events.<br /> Defines four methods to recognize when a component is<br /> hidden, moved, resized, or shown.<br /> Defines two methods to recognize when a component is<br /> added to or removed from a container.<br /> Defines two methods to recognize when a component gains<br /> or loses keyboard focus.<br /> Defines one method to recognize when the state of an<br /> item changes.<br /> Defines three methods to recognize when a key is pressed,<br /> released, or typed.<br /> Defines five methods to recognize when the mouse is clicked,<br /> enters a component, exits a component, is pressed, or is<br /> released.<br /> Defines two methods to recognize when the mouse is<br /> dragged or moved.<br /> Defines one method to recognize when the mouse wheel is<br /> moved. (Added by Java 2, version 1.4)<br /> Defines one method to recognize when a text value changes.<br /> Defines two methods to recognize when a window gains or<br /> loses input focus. (Added by Java 2, version 1.4)<br /> Defines seven methods to recognize when a window is<br /> activated, closed, deactivated, deiconified, iconified, opened,<br /> or quit.<br /> Table 20-3.<br /> Commonly Used Event Listener Interfaces</div> <div>INTERNATIONAL CONTACT INFORMATION<br /> AUSTRALIA<br /> McGraw-Hill Book Company Australia Pty. 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This makes for a much snappier response. After the menu is painted,<br /> the status line is set to reflect the newly selected item, which is also saved in oldCell.<br /> mouseReleased( )<br /> mouseReleased( ) sends the browser to the URL that corresponds to the currently selected<br /> menu item. The desired URL is then constructed. If the URL was improperly formatted<br /> in the APPLET tag, the exception is displayed on the status line and returned without<br /> attempting to switch documents. The showDocument( ) method puts the document<br /> described in the URL into the frame listed in the target array. As a final feature, the<br /> state of this SHIFT key is checked by calling the isShiftDown( ) method of MouseEvent.<br /> If SHIFT was pressed, the URL is opened into a new blank browser window instead of<br /> the one specified in target.<br /> The Code<br /> The source code for ImageMenu is shown here:<br /> import java.awt.* ;<br /> import java.awt.event.*;<br /> import java.applet.*;<br /> import java.util.*;<br /> import java.net.*;<br /> public class ImageMenu extends Applet {<br /> Dimension d;<br /> Image img, off;<br /> Graphics offg;<br /> int MAXITEMS = 64;<br /> String url[] = new String[MAXITEMS];<br /> String target[] = new String[MAXITEMS];<br /> String urlPrefix, urlSuffix;<br /> int selectedCell = -1;<br /> int oldCell = -1;<br /> int cellH;<br /> int cells;<br /> public void init() {<br /> d = getSize();<br /> urlPrefix = getParameter("urlPrefix");</div> <div>316 Java™ 2: The Complete Reference<br /> Stream Class<br /> BufferedInputStream<br /> BufferedOutputStream<br /> ByteArrayInputStream<br /> ByteArrayOutputStream<br /> DataInputStream<br /> DataOutputStream<br /> FileInputStream<br /> FileOutputStream<br /> FilterInputStream<br /> FilterOutputStream<br /> InputStream<br /> OutputStream<br /> PipedInputStream<br /> PipedOutputStream<br /> PrintStream<br /> PushbackInputStream<br /> RandomAccessFile<br /> SequenceInputStream<br /> Meaning<br /> Buffered input stream<br /> Buffered output stream<br /> Input stream that reads from a byte array<br /> Output stream that writes to a byte array<br /> An input stream that contains methods for<br /> reading the Java standard data types<br /> An output stream that contains methods for<br /> writing the Java standard data types<br /> Input stream that reads from a file<br /> Output stream that writes to a file<br /> Implements InputStream<br /> Implements OutputStream<br /> Abstract class that describes stream input<br /> Abstract class that describes stream output<br /> Input pipe<br /> Output pipe<br /> Output stream that contains print( ) and<br /> println( )<br /> Input stream that supports one-byte “unget,”<br /> which returns a byte to the input stream<br /> Supports random access file I/O<br /> Input stream that is a combination of two or<br /> more input streams that will be read<br /> sequentially, one after the other<br /> Table 12-1.<br /> The Byte Stream Classes</div> <div>THE JAVA LANGUAGE<br /> Chapter 11: Multithreaded Programming 281<br /> // Create a second thread.<br /> class NewThread implements Runnable {<br /> Thread t;<br /> }<br /> NewThread() {<br /> // Create a new, second thread<br /> t = new Thread(this, "Demo Thread");<br /> System.out.println("Child thread: " + t);<br /> t.start(); // Start the thread<br /> }<br /> // This is the entry point for the second thread.<br /> public void run() {<br /> try {<br /> for(int i = 5; i > 0; i--) {<br /> System.out.println("Child Thread: " + i);<br /> Thread.sleep(500);<br /> }<br /> } catch (InterruptedException e) {<br /> System.out.println("Child interrupted.");<br /> }<br /> System.out.println("Exiting child thread.");<br /> }<br /> class ThreadDemo {<br /> public static void main(String args[]) {<br /> new NewThread(); // create a new thread<br /> }<br /> }<br /> try {<br /> for(int i = 5; i > 0; i--) {<br /> System.out.println("Main Thread: " + i);<br /> Thread.sleep(1000);<br /> }<br /> } catch (InterruptedException e) {<br /> System.out.println("Main thread interrupted.");<br /> }<br /> System.out.println("Main thread exiting.");</div> <div>576 Java™ 2: The Complete Reference<br /> public static void wc(Reader r) throws IOException {<br /> StreamTokenizer tok = new StreamTokenizer(r);<br /> }<br /> tok.resetSyntax();<br /> tok.wordChars(33, 255);<br /> tok.whitespaceChars(0, ' ');<br /> tok.eolIsSignificant(true);<br /> while (tok.nextToken() != tok.TT_EOF) {<br /> switch (tok.ttype) {<br /> case StreamTokenizer.TT_EOL:<br /> lines++;<br /> chars++;<br /> break;<br /> case StreamTokenizer.TT_WORD:<br /> words++;<br /> default: // FALLSTHROUGH<br /> chars += tok.sval.length();<br /> break;<br /> }<br /> }<br /> public static void main(String args[]) {<br /> if (args.length == 0) { // We're working with stdin<br /> try {<br /> wc(new InputStreamReader(System.in));<br /> System.out.println(lines + " " + words + " " + chars);<br /> } catch (IOException e) {};<br /> } else { // We're working with a list of files<br /> int twords = 0, tchars = 0, tlines = 0;<br /> for (int i=0; i<args.length; i++) {<br /> try {<br /> words = chars = lines = 0;<br /> wc(new FileReader(args[i]));<br /> twords += words;<br /> tchars += chars;<br /> tlines += lines;<br /> System.out.println(args[i] + ": " +<br /> lines + " " + words + " " + chars);</div> <div>276 Java™ 2: The Complete Reference<br /> ■ A thread can be preempted by a higher-priority thread. In this case, a lower-priority<br /> thread that does not yield the processor is simply preempted—no matter what<br /> it is doing—by a higher-priority thread. Basically, as soon as a higher-priority<br /> thread wants to run, it does. This is called preemptive multitasking.<br /> In cases where two threads with the same priority are competing for CPU cycles, the<br /> situation is a bit complicated. For operating systems such as Windows 98, threads of<br /> equal priority are time-sliced automatically in round-robin fashion. For other types of<br /> operating systems, threads of equal priority must voluntarily yield control to their peers.<br /> If they don’t, the other threads will not run.<br /> Problems can arise from the differences in the way that operating systems context-switch<br /> threads of equal priority.<br /> Synchronization<br /> Because multithreading introduces an asynchronous behavior to your programs, there<br /> must be a way for you to enforce synchronicity when you need it. For example, if you<br /> want two threads to communicate and share a complicated data structure, such as a<br /> linked list, you need some way to ensure that they don’t conflict with each other. That<br /> is, you must prevent one thread from writing data while another thread is in the<br /> middle of reading it. For this purpose, Java implements an elegant twist on an age-old<br /> model of interprocess synchronization: the monitor. The monitor is a control mechanism<br /> first defined by C.A.R. Hoare. You can think of a monitor as a very small box that can<br /> hold only one thread. Once a thread enters a monitor, all other threads must wait until<br /> that thread exits the monitor. In this way, a monitor can be used to protect a shared<br /> asset from being manipulated by more than one thread at a time.<br /> Most multithreaded systems expose monitors as objects that your program must<br /> explicitly acquire and manipulate. Java provides a cleaner solution. There is no class<br /> “Monitor”; instead, each object has its own implicit monitor that is automatically entered<br /> when one of the object’s synchronized methods is called. Once a thread is inside a<br /> synchronized method, no other thread can call any other synchronized method on<br /> the same object. This enables you to write very clear and concise multithreaded code,<br /> because synchronization support is built in to the language.<br /> Messaging<br /> After you divide your program into separate threads, you need to define how they will<br /> communicate with each other. When programming with most other languages, you<br /> must depend on the operating system to establish communication between threads.<br /> This, of course, adds overhead. By contrast, Java provides a clean, low-cost way for two<br /> or more threads to talk to each other, via calls to predefined methods that all objects</div> <div>THE JAVA LIBRARY<br /> Chapter 21: Introducing the AWT: Working with Windows, Graphics, and Text 691<br /> Class<br /> ScrollPane<br /> SystemColor<br /> TextArea<br /> TextComponent<br /> TextField<br /> Toolkit<br /> Window<br /> Description<br /> A container that provides horizontal and/or vertical<br /> scroll bars for another component.<br /> Contains the colors of GUI widgets such as windows,<br /> scroll bars, text, and others.<br /> Creates a multiline edit control.<br /> A superclass for TextArea and TextField.<br /> Creates a single-line edit control.<br /> Abstract class implemented by the AWT.<br /> Creates a window with no frame, no menu bar,<br /> and no title.<br /> Table 21-1.<br /> Some AWT Classes (continued)<br /> Although the basic structure of the AWT has been the same since Java 1.0, some of the<br /> original methods were deprecated and replaced by new ones when Java 1.1 was released.<br /> For backward-compatibility, Java 2 still supports all the original 1.0 methods. However,<br /> because these methods are not for use with new code, this book does not describe them.<br /> Window Fundamentals<br /> The AWT defines windows according to a class hierarchy that adds functionality and<br /> specificity with each level. The two most common windows are those derived from<br /> Panel, which is used by applets, and those derived from Frame, which creates a<br /> standard window. Much of the functionality of these windows is derived from their<br /> parent classes. Thus, a description of the class hierarchies relating to these two classes<br /> is fundamental to their understanding. Figure 21-1 shows the class hierarchy for Panel<br /> and Frame. Let’s look at each of these classes now.<br /> Component<br /> At the top of the AWT hierarchy is the Component class. Component is an abstract<br /> class that encapsulates all of the attributes of a visual component. All user interface<br /> elements that are displayed on the screen and that interact with the user are subclasses<br /> of Component. It defines over a hundred public methods that are responsible for<br /> managing events, such as mouse and keyboard input, positioning and sizing the<br /> window, and repainting. (You already used many of these methods when you created<br /> applets in Chapters 19 and 20.) A Component object is responsible for remembering<br /> the current foreground and background colors and the currently selected text font.</div> <div>THE JAVA LANGUAGE<br /> Chapter 12: I/O, Applets, and Other Topics 343<br /> {<br /> int n = 0;<br /> for(int i=0; i < 10; i++) {<br /> assert (n = getnum()) > 0; // This is not a good idea!<br /> }<br /> }<br /> }<br /> System.out.println("n is " + n);<br /> In this version of the program, the call to getnum( ) is moved inside the assert statement.<br /> Although this works fine if assertions are enabled, it will cause a malfunction when<br /> assertions are disabled because the call to getnum( ) will never be executed! In fact, n<br /> must now be initialized, because the compiler will recognize that it might not be<br /> assigned a value by the assert statement.<br /> Assertions are a good addition to Java because they streamline the type of error<br /> checking that is common during development. For example, prior to assert, if you<br /> wanted to verify that n was positive in the preceding program, you had to use a<br /> sequence of code similar to this:<br /> if(n < 0) {<br /> System.out.println("n is negative!");<br /> return; // or throw an exception<br /> }<br /> With assert, you need only one line of code. Furthermore, you don’t have to remove<br /> the assert statements from your released code.<br /> Assertion Enabling and Disabling Options<br /> When executing code, you can disable assertions by using the -da option. You can<br /> enable or disable a specific package by specifying its name after the -ea or -da option.<br /> For example, to enable assertions in a package called MyPack, use<br /> -ea:MyPack<br /> To disable assertions in MyPack use<br /> -da:MyPack</div> <div>THE JAVA LIBRARY<br /> Chapter 14: Exploring java.lang 399<br /> Method<br /> static boolean isDefined(char ch)<br /> static boolean isDigit(char ch)<br /> static boolean isIdentifierIgnorable(char ch)<br /> static boolean isISOControl(char ch)<br /> static boolean isJavaIdentifierPart(char ch)<br /> static boolean isJavaIdentifierStart(char ch)<br /> static boolean isLetter(char ch)<br /> static boolean isLetterOrDigit(char ch)<br /> static boolean isLowerCase(char ch)<br /> static boolean isMirrored(char ch)<br /> static boolean isSpaceChar(char ch)<br /> Description<br /> Returns true if ch is defined by<br /> Unicode. Otherwise, it returns false.<br /> Returns true if ch is a digit.<br /> Otherwise, it returns false.<br /> Returns true if ch should be<br /> ignored in an identifier.<br /> Otherwise, it returns false.<br /> Returns true if ch is an ISO control<br /> character. Otherwise, it returns<br /> false.<br /> Returns true if ch is allowed as<br /> part of a Java identifier (other than<br /> the first character). Otherwise, it<br /> returns false.<br /> Returns true if ch is allowed<br /> as the first character of a<br /> Java identifier. Otherwise,<br /> it returns false.<br /> Returns true if ch is a letter.<br /> Otherwise, it returns false.<br /> Returns true if ch is a letter or a<br /> digit. Otherwise, it returns false.<br /> Returns true if ch is a<br /> lowercase letter. Otherwise,<br /> it returns false.<br /> Returns true if ch is a mirrored<br /> Unicode character. A mirrored<br /> character is one that is reversed for<br /> text that is displayed right-to-left.<br /> (Added by Java 2, version 1.4)<br /> Returns true if ch is a Unicode<br /> space character. Otherwise, it<br /> returns false.<br /> Table 14-7.<br /> Various Character Methods</div> <div>Part III<br /> Software Development Using Java</div> <div>808 Java™ 2: The Complete Reference<br /> Figure 23-2.<br /> Sample output from ObservedImageLoad<br /> is called double buffering, because the screen is considered a buffer for pixels, and the<br /> offscreen image is the second buffer, where you can prepare pixels for display.<br /> Earlier in this chapter, you saw how to create a blank Image object. Now you will<br /> see how to draw on that image rather than the screen. As you recall from earlier<br /> chapters, you need a Graphics object in order to use any of Java’s rendering methods.<br /> Conveniently, the Graphics object that you can use to draw on an Image is available<br /> via the getGraphics( ) method. Here is a code fragment that creates a new image,<br /> obtains its graphics context, and fills the entire image with red pixels:</div> <div>THE JAVA LIBRARY<br /> Chapter 23: Images 833<br /> public void setHints(int dummy) { }<br /> public synchronized void imageComplete(int dummy) {<br /> notifyAll();<br /> }<br /> public void setDimensions(int x, int y) {<br /> width = x;<br /> height = y;<br /> imgpixels = new int[x*y];<br /> }<br /> public void setPixels(int x1, int y1, int w, int h,<br /> ColorModel model, byte pixels[], int off, int scansize) {<br /> int pix, x, y, x2, y2, sx, sy;<br /> }<br /> x2 = x1+w;<br /> y2 = y1+h;<br /> sy = off;<br /> for(y=y1; y<y2; y++) {<br /> sx = sy;<br /> for(x=x1; x<x2; x++) {<br /> pix = model.getRGB(pixels[sx++]);<br /> if((pix & 0xff000000) == 0)<br /> pix = 0x00ffffff;<br /> imgpixels[y*width+x] = pix;<br /> }<br /> sy += scansize;<br /> }<br /> public void setPixels(int x1, int y1, int w, int h,<br /> ColorModel model, int pixels[], int off, int scansize) {<br /> int pix, x, y, x2, y2, sx, sy;<br /> x2 = x1+w;<br /> y2 = y1+h;<br /> sy = off;<br /> for(y=y1; y<y2; y++) {<br /> sx = sy;<br /> for(x=x1; x<x2; x++) {</div> <div>916 Java™ 2: The Complete Reference<br /> handles, and it doesn’t matter which one you choose. Begin by wiring a connection<br /> from the slider to the scroll bar, as shown in Figure 25-10.<br /> After you have completed the connection, the Interaction Wizard will appear. It<br /> lets you specify how the two components communicate. In this case, you will define<br /> what takes place when the slider is moved. On the first page you will select the event<br /> method that will be called when the source object (in this case, the slider) changes<br /> position. First, select the Event Adapter radio button (if it is not already selected).<br /> Figure 25-10.<br /> Wiring a connection from the slider to the scroll bar</div> <div>416 Java™ 2: The Complete Reference<br /> Class<br /> Class encapsulates the run-time state of an object or interface. Objects of type Class are<br /> created automatically, when classes are loaded. You cannot explicitly declare a Class<br /> object. Generally, you obtain a Class object by calling the getClass( ) method defined<br /> by Object. Some of the most commonly used methods defined by Class are shown in<br /> Table 14-13.<br /> Method<br /> static Class forName(String name)<br /> throws ClassNotFoundException<br /> static Class forName(String name,<br /> boolean how,<br /> ClassLoader ldr)<br /> throws ClassNotFoundException<br /> Class[ ] getClasses( )<br /> ClassLoader getClassLoader( )<br /> Constructor[ ] getConstructors( )<br /> throws SecurityException<br /> Constructor[ ] getDeclaredConstructors( )<br /> throws SecurityException<br /> Field[ ] getDeclaredFields( )<br /> throws SecurityException<br /> Method[ ] getDeclaredMethods( )<br /> throws SecurityException<br /> Description<br /> Returns a Class object given its<br /> complete name.<br /> Returns a Class object given its<br /> complete name. The object is<br /> loaded using the loader specified<br /> by ldr. If how is true, the object is<br /> initialized; otherwise it is not.<br /> (Added by Java 2)<br /> Returns a Class object for each of<br /> the public classes and interfaces that<br /> are members of the invoking object.<br /> Returns the ClassLoader object that<br /> loaded the class or interface used to<br /> instantiate the invoking object.<br /> Returns a Constructor object for all<br /> the public constructors of this class.<br /> Returns a Constructor object for all<br /> the constructors that are declared by<br /> this class.<br /> Returns a Field object for all the<br /> fields that are declared by this class.<br /> Returns a Method object for all the<br /> methods that are declared by this<br /> class or interface.<br /> Table 14-13.<br /> Some Methods Defined by Class</div> <div>508 Java™ 2: The Complete Reference<br /> The output from this program is shown here:<br /> title Java: The Complete Reference<br /> author Schildt<br /> publisher Osborne/McGraw-Hill<br /> copyright 2002<br /> BitSet<br /> A BitSet class creates a special type of array that holds bit values. This array can<br /> increase in size as needed. This makes it similar to a vector of bits. The BitSet<br /> constructors are shown here:<br /> BitSet( )<br /> BitSet(int size)<br /> The first version creates a default object. The second version allows you to specify its<br /> initial size (that is, the number of bits that it can hold). All bits are initialized to zero.<br /> BitSet implements the Cloneable interface and defines the methods listed in<br /> Table 16-2. Notice that several were added by Java 2, version 1.4.<br /> Method<br /> void and(BitSet bitSet)<br /> void andNot(BitSet bitSet)<br /> int cardinality( )<br /> Description<br /> ANDs the contents of the invoking BitSet<br /> object with those specified by bitSet. The result<br /> is placed into the invoking object.<br /> For each 1 bit in bitSet, the corresponding bit in<br /> the invoking BitSet is cleared. (Added by Java 2)<br /> Returns the number of set bits in the invoking<br /> object. (Added by Java 2, version 1.4)<br /> void clear( ) Zeros all bits. (Added by Java 2, version 1.4)<br /> void clear(int index)<br /> Zeros the bit specified by index.<br /> void clear(int startIndex,<br /> int endIndex)<br /> Object clone( )<br /> boolean equals(Object bitSet)<br /> Zeros the bits from startIndex to endIndex–1.<br /> (Added by Java 2, version 1.4)<br /> Duplicates the invoking BitSet object.<br /> Returns true if the invoking bit set is<br /> equivalent to the one passed in bitSet.<br /> Otherwise, the method returns false.<br /> Table 16-2.<br /> The Methods Defined by BitSet</div> <div>THE JAVA LANGUAGE<br /> Chapter 7: A Closer Look at Methods and Classes 175<br /> }<br /> // Pop an item from the stack<br /> int pop() {<br /> if(tos < 0) {<br /> System.out.println("Stack underflow.");<br /> return 0;<br /> }<br /> else<br /> return stck[tos--];<br /> }<br /> As you can see, now both stck, which holds the stack, and tos, which is the index of<br /> the top of the stack, are specified as private. This means that they cannot be accessed or<br /> altered except through push( ) and pop( ). Making tos private, for example, prevents<br /> other parts of your program from inadvertently setting it to a value that is beyond the<br /> end of the stck array.<br /> The following program demonstrates the improved Stack class. Try removing the<br /> commented-out lines to prove to yourself that the stck and tos members are, indeed,<br /> inaccessible.<br /> class TestStack {<br /> public static void main(String args[]) {<br /> Stack mystack1 = new Stack();<br /> Stack mystack2 = new Stack();<br /> // push some numbers onto the stack<br /> for(int i=0; i<10; i++) mystack1.push(i);<br /> for(int i=10; i<20; i++) mystack2.push(i);<br /> // pop those numbers off the stack<br /> System.out.println("Stack in mystack1:");<br /> for(int i=0; i<10; i++)<br /> System.out.println(mystack1.pop());<br /> System.out.println("Stack in mystack2:");<br /> for(int i=0; i<10; i++)<br /> System.out.println(mystack2.pop());<br /> // these statements are not legal<br /> // mystack1.tos = -2;<br /> // mystack2.stck[3] = 100;</div> <div>306 Java™ 2: The Complete Reference<br /> }<br /> }<br /> }<br /> } catch (InterruptedException e) {<br /> System.out.println(name + " interrupted.");<br /> }<br /> System.out.println(name + " exiting.");<br /> class SuspendResume {<br /> public static void main(String args[]) {<br /> NewThread ob1 = new NewThread("One");<br /> NewThread ob2 = new NewThread("Two");<br /> }<br /> }<br /> try {<br /> Thread.sleep(1000);<br /> ob1.t.suspend();<br /> System.out.println("Suspending thread One");<br /> Thread.sleep(1000);<br /> ob1.t.resume();<br /> System.out.println("Resuming thread One");<br /> ob2.t.suspend();<br /> System.out.println("Suspending thread Two");<br /> Thread.sleep(1000);<br /> ob2.t.resume();<br /> System.out.println("Resuming thread Two");<br /> } catch (InterruptedException e) {<br /> System.out.println("Main thread Interrupted");<br /> }<br /> // wait for threads to finish<br /> try {<br /> System.out.println("Waiting for threads to finish.");<br /> ob1.t.join();<br /> ob2.t.join();<br /> } catch (InterruptedException e) {<br /> System.out.println("Main thread Interrupted");<br /> }<br /> System.out.println("Main thread exiting.");</div> <div>Chapter 21<br /> Introducing the AWT:<br /> Working with Windows,<br /> Graphics, and Text<br /> 687</div> <div>THE JAVA LANGUAGE<br /> Chapter 5: Control Statements 109<br /> Iteration Statements<br /> Java’s iteration statements are for, while, and do-while. These statements create what<br /> we commonly call loops. As you probably know, a loop repeatedly executes the same<br /> set of instructions until a termination condition is met. As you will see, Java has a loop<br /> to fit any programming need.<br /> while<br /> The while loop is Java’s most fundamental looping statement. It repeats a statement or<br /> block while its controlling expression is true. Here is its general form:<br /> while(condition) {<br /> // body of loop<br /> }<br /> The condition can be any Boolean expression. The body of the loop will be executed as<br /> long as the conditional expression is true. When condition becomes false, control passes<br /> to the next line of code immediately following the loop. The curly braces are unnecessary<br /> if only a single statement is being repeated.<br /> Here is a while loop that counts down from 10, printing exactly ten lines of “tick”:<br /> // Demonstrate the while loop.<br /> class While {<br /> public static void main(String args[]) {<br /> int n = 10;<br /> }<br /> }<br /> while(n > 0) {<br /> System.out.println("tick " + n);<br /> n--;<br /> }<br /> When you run this program, it will “tick” ten times:<br /> tick 10<br /> tick 9<br /> tick 8<br /> tick 7<br /> tick 6<br /> tick 5<br /> tick 4</div> <div>380 Java™ 2: The Complete Reference<br /> This chapter discusses those classes and interfaces defined by java.lang. As you<br /> know, java.lang is automatically imported into all programs. It contains classes<br /> and interfaces that are fundamental to virtually all of Java programming. It is<br /> Java’s most widely used package.<br /> java.lang includes the following classes:<br /> Boolean Long StackTraceElement (Java 2,1.4)<br /> Byte Math StrictMath (Java 2,1.3)<br /> Character Number String<br /> Class Object StringBuffer<br /> ClassLoader Package (Java 2) System<br /> Compiler Process Thread<br /> Double Runtime ThreadGroup<br /> Float RuntimePermission (Java 2) ThreadLocal (Java 2)<br /> InheritableThreadLocal (Java 2) SecurityManager Throwable<br /> Integer Short Void<br /> In addition, there are two classes defined by Character: Character.Subset and<br /> Character.UnicodeBlock. These were added by Java 2.<br /> java.lang also defines the following interfaces:<br /> ■ Cloneable<br /> ■ Comparable<br /> ■ Runnable<br /> ■ CharSequence<br /> The Comparable interface was added by Java 2. CharSequence was added by Java 2,<br /> version 1.4.<br /> Several of the classes contained in java.lang contain deprecated methods, most<br /> dating back to Java 1.0. These deprecated methods are still provided by Java 2, to<br /> support an ever-shrinking pool of legacy code, and are not recommended for new code.<br /> Most of the deprecations took place prior to Java 2 and these deprecated methods are not<br /> discussed here. Deprecations that occurred because of Java 2, however, are mentioned.<br /> Java 2 also added several new classes and methods to the java.lang package. The<br /> new additions are so indicated.<br /> Simple Type Wrappers<br /> As we mentioned in Part I of this book, Java uses simple types, such as int and char, for<br /> performance reasons. These data types are not part of the object hierarchy. They are</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 28: Migrating from C++ to Java 999<br /> The only reason that this class cannot be made into a Java interface is the existence<br /> of isOK. Presumably, isOK is used to indicate some status associated with the class.<br /> However, if you think about it, there really is no reason for isOK to be defined as a<br /> variable. Instead, you could specify a method called isOK( ) that returns the status.<br /> In this approach, isOK( ) will be defined, along with the other methods, by any<br /> implementing class. Thus, you could convert the preceding C++ abstract class into<br /> the following Java interface:<br /> interface SomeClass {<br /> int f1();<br /> void f2(int i);<br /> double f3();<br /> int f4(int a, char ch);<br /> boolean isOK();<br /> }<br /> Many abstract classes in C++ can—and should—be converted into interfaces when<br /> you move code to Java. In doing so, you will probably find that it clarifies the structure<br /> of the class hierarchy.<br /> Converting Default Arguments<br /> One extensively used feature of C++ that Java does not support is default function<br /> arguments. For example, the area( ) function shown in the following C++ program<br /> computes the area of a rectangle if called with two arguments, or the area of a square<br /> if called with one argument.<br /> // C++ program that uses default arguments.<br /> #include <iostream><br /> using namespace std;<br /> /* Compute area of a rectangle. For a square,<br /> pass only one argument.<br /> */<br /> double area(double l, double w=0) {<br /> if(w==0) return l * l;<br /> else return l * w;<br /> }<br /> int main()<br /> {<br /> cout << "Area of 2.2 by 3.4 rectangle: ";<br /> cout << area(2.2, 3.4) << endl;</div> <div>892 Java™ 2: The Complete Reference<br /> JAR technology makes it much easier to deliver and install software. Also, the<br /> elements in a JAR file are compressed, which makes downloading a JAR file much<br /> faster than separately downloading several uncompressed files. Digital signatures may<br /> also be associated with the individual elements in a JAR file. This allows a consumer to<br /> be sure that these elements were produced by a specific organization or individual.<br /> The package java.util.zip contains classes that read and write JAR files.<br /> Manifest Files<br /> A developer must provide a manifest file to indicate which of the components in a JAR<br /> file are Java Beans. An example of a manifest file is provided in the following listing. It<br /> defines a JAR file that contains four .gif files and one .class file. The last entry is a Bean.<br /> Name: sunw/demo/slides/slide0.gif<br /> Name: sunw/demo/slides/slide1.gif<br /> Name: sunw/demo/slides/slide2.gif<br /> Name: sunw/demo/slides/slide3.gif<br /> Name: sunw/demo/slides/Slides.class<br /> Java-Bean: True<br /> A manifest file may reference several .class files. If a .class file is a Java Bean, its<br /> entry must be immediately followed by the line “Java-Bean: True”.<br /> The JAR Utility<br /> A utility is used to generate a JAR file. Its syntax is shown here:<br /> jar options files<br /> Table 25-1 lists the possible options and their meanings. The following examples show<br /> how to use this utility.<br /> Creating a JAR File<br /> The following command creates a JAR file named Xyz.jar that contains all of the .class<br /> and .gif files in the current directory:<br /> jar cf Xyz.jar *.class *.gif<br /> If a manifest file such as Yxz.mf is available, it can be used with the following command:<br /> jar cfm Xyz.jar Yxz.mf *.class *.gif</div> <div>THE JAVA LANGUAGE<br /> Chapter 9: Packages and Interfaces 243<br /> /* Create an interface variable and<br /> access stacks through it.<br /> */<br /> class IFTest3 {<br /> public static void main(String args[]) {<br /> IntStack mystack; // create an interface reference variable<br /> DynStack ds = new DynStack(5);<br /> FixedStack fs = new FixedStack(8);<br /> mystack = ds; // load dynamic stack<br /> // push some numbers onto the stack<br /> for(int i=0; i<12; i++) mystack.push(i);<br /> mystack = fs; // load fixed stack<br /> for(int i=0; i<8; i++) mystack.push(i);<br /> mystack = ds;<br /> System.out.println("Values in dynamic stack:");<br /> for(int i=0; i<12; i++)<br /> System.out.println(mystack.pop());<br /> }<br /> }<br /> mystack = fs;<br /> System.out.println("Values in fixed stack:");<br /> for(int i=0; i<8; i++)<br /> System.out.println(mystack.pop());<br /> In this program, mystack is a reference to the IntStack interface. Thus, when it refers to<br /> ds, it uses the versions of push( ) and pop( ) defined by the DynStack implementation.<br /> When it refers to fs, it uses the versions of push( ) and pop( ) defined by FixedStack.<br /> As explained, these determinations are made at run time. Accessing multiple<br /> implementations of an interface through an interface reference variable is the most<br /> powerful way that Java achieves run-time polymorphism.<br /> Variables in Interfaces<br /> You can use interfaces to import shared constants into multiple classes by simply<br /> declaring an interface that contains variables which are initialized to the desired<br /> values. When you include that interface in a class (that is, when you “implement” the<br /> interface), all of those variable names will be in scope as constants. This is similar to<br /> using a header file in C/C++ to create a large number of #defined constants or const<br /> declarations. If an interface contains no methods, then any class that includes such an<br /> interface doesn’t actually implement anything. It is as if that class were importing the</div> <div>APPLYING JAVA<br /> Chapter 29: The DynamicBillboard Applet 1029<br /> FadeTransition.java<br /> The FadeTransition class changes one image into another by randomly including a<br /> number of new pixels from the next billboard in each successive cell frame. This makes<br /> the next billboard appear to fade in over the old billboard.<br /> The heart of this transition is a two-dimensional array of short integers called<br /> random. This array holds an index for every element in the next billboard’s image pixel<br /> array. These indexes are randomly distributed in the two-dimensional array. The eight<br /> elements in the first dimension of this array will be used when cells are created, one for<br /> each new cell. The last element is never actually used, because there are only seven<br /> cells. It is included when the random array is created to ensure that the indexes are<br /> randomly distributed correctly.<br /> The FadeTransition uses this array to pick pixels from the next billboard to<br /> overwrite pixels of the old billboard. For the first cell, the work_pixels array contains<br /> nothing but pixels from the old billboard. One-eighth of these pixels get changed to<br /> the next billboard’s pixels. For the following cell, the same work_pixels array is used,<br /> and one-eighth more pixels are filled in from the next billboard. For this cell the<br /> result has one-fourth of the pixels from the next billboard, while the remainder are<br /> from the old billboard. This continues until the last cell, cell number seven, which has<br /> seven-eighths of its pixels from the new billboard. Remember, the DynamicBillboard<br /> applet simply uses the whole image from the next billboard after the last cell to<br /> complete the transition.<br /> Because the size of this two-dimensional array is dependent on the size of the<br /> applet, it must be unique to each applet. Using a static variable to store this array is<br /> unacceptable, because applets of different sizes would share this array. Since it is fairly<br /> time-consuming to create this array, it does not make sense to re-create it every time<br /> this transition is to be used.<br /> This is where the superclass’ static variable, object_table, first comes into play.<br /> Once this array is created, it can be stored in this hash table with a key that includes the<br /> size of the applet. When the array needs to be used, the applet can get the appropriate<br /> one out of the hash table. If it does not exist in the hash table, the applet can then create<br /> the array and store it in the hash table for future use. New applets of the same size as<br /> the current applet will benefit from a usable array already being there. This seems like<br /> a lot of effort, but in practice, web sites tend to use this applet on a large number of<br /> pages with a standard layout size for each banner advertisement. So, it saves an<br /> enormous amount of memory and CPU time to cache these tables.</div> <div>764 Java™ 2: The Complete Reference<br /> Here, layoutObj is a reference to the desired layout manager. If you wish to disable the<br /> layout manager and position components manually, pass null for layoutObj. If you do<br /> this, you will need to determine the shape and position of each component manually,<br /> using the setBounds( ) method defined by Component. Normally, you will want to<br /> use a layout manager.<br /> Each layout manager keeps track of a list of components that are stored by their<br /> names. The layout manager is notified each time you add a component to a container.<br /> Whenever the container needs to be resized, the layout manager is consulted via its<br /> minimumLayoutSize( ) and preferredLayoutSize( ) methods. Each component<br /> that is being managed by a layout manager contains the getPreferredSize( ) and<br /> getMinimumSize( ) methods. These return the preferred and minimum size required<br /> to display each component. The layout manager will honor these requests if at all<br /> possible, while maintaining the integrity of the layout policy. You may override<br /> these methods for controls that you subclass. Default values are provided otherwise.<br /> Java has several predefined LayoutManager classes, several of which are described<br /> next. You can use the layout manager that best fits your application.<br /> FlowLayout<br /> FlowLayout is the default layout manager. This is the layout manager that the preceding<br /> examples have used. FlowLayout implements a simple layout style, which is similar to<br /> how words flow in a text editor. Components are laid out from the upper-left corner, left<br /> to right and top to bottom. When no more components fit on a line, the next one appears<br /> on the next line. A small space is left between each component, above and below, as well<br /> as left and right. Here are the constructors for FlowLayout:<br /> FlowLayout( )<br /> FlowLayout(int how)<br /> FlowLayout(int how, int horz, int vert)<br /> The first form creates the default layout, which centers components and leaves five<br /> pixels of space between each component. The second form lets you specify how each<br /> line is aligned. Valid values for how are as follows:<br /> FlowLayout.LEFT<br /> FlowLayout.CENTER<br /> FlowLayout.RIGHT<br /> These values specify left, center, and right alignment, respectively. The third form<br /> allows you to specify the horizontal and vertical space left between components in<br /> horz and vert, respectively.<br /> Here is a version of the CheckboxDemo applet shown earlier in this chapter,<br /> modified so that it uses left-aligned flow layout.</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 25: Java Beans 901<br /> Generate a JAR File<br /> Beans are included in the ToolBox window of the BDK only if they are in JAR files in the<br /> directory c:\bdk\jars. These files are generated with the jar utility. Enter the following:<br /> jar cfm ..\jars\colors.jar colors.mft sunw\demo\colors\*.class<br /> This command creates the file colors.jar and places it in the directory c:\bdk\jars.<br /> (You may wish to put this in a batch file for future use.)<br /> Start the BDK<br /> Change to the directory c:\bdk\beanbox and type run. This causes the BDK to start.<br /> You should see three windows, titled ToolBox, BeanBox, and Properties. The ToolBox<br /> window should include an entry labeled “Colors” for your new Bean.<br /> Create an Instance of the Colors Bean<br /> After you complete the preceding steps, create an instance of the Colors Bean in the<br /> BeanBox window. Test your new component by pressing the mouse anywhere within<br /> its borders. Its color immediately changes. Use the Properties window to change the<br /> rectangular property from false to true. Its shape immediately changes.<br /> Create and Configure an Instance of the OurButton Bean<br /> Create an instance of the OurButton Bean in the BeanBox window. Then follow<br /> these steps:<br /> 1. Go to the Properties window and change the label of the Bean to “Change”.<br /> You should see that the button appearance changes immediately when this<br /> property is changed.<br /> 2. Go to the menu bar of the BeanBox and select Edit | Events | action |<br /> actionPerformed.<br /> 3. Move the cursor so that it is inside the Colors Bean display area, and click the<br /> left mouse button. You should see the Event Target Dialog dialog box.<br /> 4. The dialog box allows you to choose a method that should be invoked when<br /> this button is clicked. Select the entry labeled “change” and click the OK button.<br /> You should see a message box appear very briefly, stating that the tool is<br /> “Generating and compiling adaptor class.”<br /> 5. Click on the button. You should see the color change.<br /> You might want to experiment with the Colors Bean a bit before moving on.</div> <div>46 Java™ 2: The Complete Reference<br /> floating-point types and operators. There are two kinds of floating-point types, float<br /> and double, which represent single- and double-precision numbers, respectively. Their<br /> width and ranges are shown here:<br /> Name Width in Bits Approximate Range<br /> double 64 4.9e–324 to 1.8e+308<br /> float 32 1.4e−045 to 3.4e+038<br /> Each of these floating-point types is examined next.<br /> float<br /> The type float specifies a single-precision value that uses 32 bits of storage. Single<br /> precision is faster on some processors and takes half as much space as double precision,<br /> but will become imprecise when the values are either very large or very small. Variables<br /> of type float are useful when you need a fractional component, but don’t require a<br /> large degree of precision. For example, float can be useful when representing dollars<br /> and cents.<br /> Here are some example float variable declarations:<br /> float hightemp, lowtemp;<br /> double<br /> Double precision, as denoted by the double keyword, uses 64 bits to store a value. Double<br /> precision is actually faster than single precision on some modern processors that have<br /> been optimized for high-speed mathematical calculations. All transcendental math<br /> functions, such as sin( ), cos( ), and sqrt( ), return double values. When you need to<br /> maintain accuracy over many iterative calculations, or are manipulating large-valued<br /> numbers, double is the best choice.<br /> Here is a short program that uses double variables to compute the area of a circle:<br /> // Compute the area of a circle.<br /> class Area {<br /> public static void main(String args[]) {<br /> double pi, r, a;<br /> r = 10.8; // radius of circle<br /> pi = 3.1416; // pi, approximately<br /> a = pi * r * r; // compute area</div> <div>746 Java™ 2: The Complete Reference<br /> be selected at any one time. To create a set of mutually exclusive check boxes, you must<br /> first define the group to which they will belong and then specify that group when you<br /> construct the check boxes. Check box groups are objects of type CheckboxGroup. Only<br /> the default constructor is defined, which creates an empty group.<br /> You can determine which check box in a group is currently selected by calling<br /> getSelectedCheckbox( ). You can set a check box by calling setSelectedCheckbox( ).<br /> These methods are as follows:<br /> Checkbox getSelectedCheckbox( )<br /> void setSelectedCheckbox(Checkbox which)<br /> Here, which is the check box that you want to be selected. The previously selected check<br /> box will be turned off.<br /> Here is a program that uses check boxes that are part of a group:<br /> // Demonstrate check box group.<br /> import java.awt.*;<br /> import java.awt.event.*;<br /> import java.applet.*;<br /> /*<br /> <applet code="CBGroup" width=250 height=200><br /> </applet><br /> */<br /> public class CBGroup extends Applet implements ItemListener {<br /> String msg = "";<br /> Checkbox Win98, winNT, solaris, mac;<br /> CheckboxGroup cbg;<br /> public void init() {<br /> cbg = new CheckboxGroup();<br /> Win98 = new Checkbox("Windows 98/XP", cbg, true);<br /> winNT = new Checkbox("Windows NT/2000", cbg, false);<br /> solaris = new Checkbox("Solaris", cbg, false);<br /> mac = new Checkbox("MacOS", cbg, false);<br /> add(Win98);<br /> add(winNT);<br /> add(solaris);<br /> add(mac);<br /> Win98.addItemListener(this);</div> <div>THE JAVA LANGUAGE<br /> Chapter 11: Multithreaded Programming 287<br /> // Using join() to wait for threads to finish.<br /> class NewThread implements Runnable {<br /> String name; // name of thread<br /> Thread t;<br /> }<br /> NewThread(String threadname) {<br /> name = threadname;<br /> t = new Thread(this, name);<br /> System.out.println("New thread: " + t);<br /> t.start(); // Start the thread<br /> }<br /> // This is the entry point for thread.<br /> public void run() {<br /> try {<br /> for(int i = 5; i > 0; i--) {<br /> System.out.println(name + ": " + i);<br /> Thread.sleep(1000);<br /> }<br /> } catch (InterruptedException e) {<br /> System.out.println(name + " interrupted.");<br /> }<br /> System.out.println(name + " exiting.");<br /> }<br /> class DemoJoin {<br /> public static void main(String args[]) {<br /> NewThread ob1 = new NewThread("One");<br /> NewThread ob2 = new NewThread("Two");<br /> NewThread ob3 = new NewThread("Three");<br /> System.out.println("Thread One is alive: "<br /> + ob1.t.isAlive());<br /> System.out.println("Thread Two is alive: "<br /> + ob2.t.isAlive());<br /> System.out.println("Thread Three is alive: "<br /> + ob3.t.isAlive());<br /> // wait for threads to finish<br /> try {<br /> System.out.println("Waiting for threads to finish.");<br /> ob1.t.join();</div> <div>THE JAVA LIBRARY<br /> Chapter 22: Using AWT Controls, Layout Managers, and Menus 755<br /> thumb, the user can click to cause the thumb to jump in that direction by some increment<br /> larger than 1. Typically, this action translates into some form of page up and page down.<br /> Scroll bars are encapsulated by the Scrollbar class.<br /> Scrollbar defines the following constructors:<br /> Scrollbar( )<br /> Scrollbar(int style)<br /> Scrollbar(int style, int initialValue, int thumbSize, int min, int max)<br /> The first form creates a vertical scroll bar. The second and third forms allow you to<br /> specify the orientation of the scroll bar. If style is Scrollbar.VERTICAL, a vertical scroll<br /> bar is created. If style is Scrollbar.HORIZONTAL, the scroll bar is horizontal. In the<br /> third form of the constructor, the initial value of the scroll bar is passed in initialValue.<br /> The number of units represented by the height of the thumb is passed in thumbSize.<br /> The minimum and maximum values for the scroll bar are specified by min and max.<br /> If you construct a scroll bar by using one of the first two constructors, then you<br /> need to set its parameters by using setValues( ), shown here, before it can be used:<br /> void setValues(int initialValue, int thumbSize, int min, int max)<br /> The parameters have the same meaning as they have in the third constructor just<br /> described.<br /> To obtain the current value of the scroll bar, call getValue( ). It returns the current<br /> setting. To set the current value, call setValue( ). These methods are as follows:<br /> int getValue( )<br /> void setValue(int newValue)<br /> Here, newValue specifies the new value for the scroll bar. When you set a value, the<br /> slider box inside the scroll bar will be positioned to reflect the new value.<br /> You can also retrieve the minimum and maximum values via getMinimum( ) and<br /> getMaximum( ), shown here:<br /> int getMinimum( )<br /> int getMaximum( )<br /> They return the requested quantity.<br /> By default, 1 is the increment added to or subtracted from the scroll bar each<br /> time it is scrolled up or down one line. You can change this increment by calling<br /> setUnitIncrement( ). Bydefault, page-up and page-down increments are 10. You can<br /> change this value by calling setBlockIncrement( ). These methods are shown here:<br /> void setUnitIncrement(int newIncr)<br /> void setBlockIncrement(int newIncr)</div> <div>552 Java™ 2: The Complete Reference<br /> ByteArrayInputStream<br /> ByteArrayInputStream is an implementation of an input stream that uses a byte array<br /> as the source. This class has two constructors, each of which requires a byte array to<br /> provide the data source:<br /> ByteArrayInputStream(byte array[ ])<br /> ByteArrayInputStream(byte array[ ], int start, int numBytes)<br /> Here, array is the input source. The second constructor creates an InputStream from a<br /> subset of your byte array that begins with the character at the index specified by start<br /> and is numBytes long.<br /> The following example creates a pair of ByteArrayInputStreams, initializing them<br /> with the byte representation of the alphabet:<br /> // Demonstrate ByteArrayInputStream.<br /> import java.io.*;<br /> class ByteArrayInputStreamDemo {<br /> public static void main(String args[]) throws IOException {<br /> String tmp = "abcdefghijklmnopqrstuvwxyz";<br /> byte b[] = tmp.getBytes();<br /> ByteArrayInputStream input1 = new ByteArrayInputStream(b);<br /> ByteArrayInputStream input2 = new ByteArrayInputStream(b, 0,3);<br /> }<br /> }<br /> The input1 object contains the entire lowercase alphabet, while input2 contains only<br /> the first three letters.<br /> A ByteArrayInputStream implements both mark( ) and reset( ). However, if mark( )<br /> has not been called, then reset( ) sets the stream pointer to the start of the stream—which<br /> in this case is the start of the byte array passed to the constructor. The next example<br /> shows how to use the reset( ) method to read the same input twice. In this case, we read<br /> and print the letters “abc” once in lowercase and then again in uppercase.<br /> import java.io.*;<br /> class ByteArrayInputStreamReset {<br /> public static void main(String args[]) throws IOException {<br /> String tmp = "abc";<br /> byte b[] = tmp.getBytes();</div> <div>SOFTWARE DEVELOPMENT<br /> USING JAVA<br /> Chapter 27: Servlets 951<br /> machine. You will see that some servlets are trusted and others are untrusted. Finally,<br /> the full functionality of the Java class libraries is available to a servlet. It can communicate<br /> with applets, databases, or other software via the sockets and RMI mechanisms that<br /> you have seen already.<br /> The Life Cycle of a Servlet<br /> Three methods are central to the life cycle of a servlet. These are init( ), service( ),<br /> and destroy( ). They are implemented by every servlet and are invoked at specific<br /> times by the server. Let us consider a typical user scenario to understand when these<br /> methods are called.<br /> First, assume that a user enters a Uniform Resource Locator (URL) to a Web<br /> browser. The browser then generates an HTTP request for this URL. This request is<br /> then sent to the appropriate server.<br /> Second, this HTTP request is received by the Web server. The server maps this<br /> request to a particular servlet. The servlet is dynamically retrieved and loaded into<br /> the address space of the server.<br /> Third, the server invokes the init( ) method of the servlet. This method is invoked<br /> only when the servlet is first loaded into memory. It is possible to pass initialization<br /> parameters to the servlet so it may configure itself.<br /> Fourth, the server invokes the service( ) method of the servlet. This method is<br /> called to process the HTTP request. You will see that it is possible for the servlet to<br /> read data that has been provided in the HTTP request. It may also formulate an<br /> HTTP response for the client.<br /> The servlet remains in the server’s address space and is available to process any<br /> other HTTP requests received from clients. The service( ) method is called for each<br /> HTTP request.<br /> Finally, the server may decide to unload the servlet from its memory. The algorithms<br /> by which this determination is made are specific to each server. T
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