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Class LogoApplet (Fig. 18.4) defines an init method in which the three HTML parameters are read with Applet method getParameter (lines 31, 37 and 40). After the applet reads these parameters and the two integer parameters are converted to int values, the if/else structure at lines 48 through 51 creates a LogoAnimator2 and calls its three-argument constructor. If the imageName is null or totalImages is 0, the applet calls the default LogoAnimator2 constructor and uses the default animation. Otherwise, the applet passes totalImages, animationDelay and imageName to the three-argument LogoAnimator2 constructor, and the constructor uses those arguments to customize the animation. LogoAnimator2’s three-argument constructor invokes LogoAnimator’s initalizeAnimation method to load the images and determine the width and height of the animation.
18.5 Image Maps
Image maps are a common technique used to create interactive Web pages. An image map is an image that has hot areas that the user can click to accomplish a task, such as loading a different Web page into a browser. When the user positions the mouse pointer over a hot area, normally a descriptive message appears in the status area of the browser or in a popup window.
Figure 18.5 loads an image containing several of the common tip icons used throughout this book. The program allows the user to position the mouse pointer over an icon and display a descriptive message for the icon. Event handler mouseMoved (lines 42–46) takes the mouse coordinates and passes them to method translateLocation (lines 63–76). Method translateLocation tests the coordinates to determine the icon over which the mouse was positioned when the mouseMoved event occurred. Method translateLocation then returns a message indicating what the icon represents. This message is displayed in the appletviewer’s (or browser’s) status bar.
1// Fig. 18.5: ImageMap.java
2 // Demonstrating an image map.
3
4 // Java core packages
5import java.awt.*;
6 import java.awt.event.*;
7
8 // Java extension packages
9 import javax.swing.*;
10
11public class ImageMap extends JApplet {
12private ImageIcon mapImage;
13
14private String captions[] = { "Common Programming Error",
15"Good Programming Practice",
16"Graphical User Interface Tip", "Performance Tip",
17"Portability Tip", "Software Engineering Observation",
18"Testing and Debugging Tip" };
19
Fig. 18.5 Demonstrating an image map (part 1 of 4).
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Base or getCodeBase method. Method getDocumentBase indicates the location of the HTML file that loaded the applet (if the applet is in a package, this indicates the location of the package or JAR file containing the package). Method getCodeBase indicates the location of the applet’s .class file. The second version of method play takes a URL that contains the location and the file name of the audio clip. The statement
play( getDocumentBase(), "hi.au" );
loads the audio clip in file hi.au and plays it once.
The sound engine that plays the audio clips supports several audio file formats, including Sun Audio file format (.au extension), Windows Wave file format (.wav extension), Macintosh AIFF file format (.aif or .aiff extension) and Musical Instrument Digital Interface (MIDI) file format (.mid or .rmi extensions). The Java Media Framework (JMF) and Java Sound APIs support additional formats.
The program of Fig. 18.6 demonstrates loading and playing an AudioClip (package java.applet). This technique is more flexible than Applet method play. An applet can use an AudioClip to store audio for repeated use throughout the program’s execution. Applet method getAudioClip has two forms that take the same arguments as method play described previously. Method getAudioClip returns a reference to an AudioClip. An AudioClip has three methods—play, loop and stop. Method play plays the audio once. Method loop continuously loops the audio clip in the background. Method stop terminates an audio clip that is currently playing. In the program, each of these methods is associated with a button on the applet.
Lines 62–63 in the applet’s init method use getAudioClip to load two audio files—a Windows Wave file (welcome.wav) and a Sun Audio file (hi.au). The user can select which audio clip to play from JComboBox chooseSound. Notice that the applet’s stop method is overridden at lines 69–72. When the user switches Web pages, the applet container calls the applet’s stop method. This enables the applet to stop playing the audio clip. Otherwise, the audio clip continues to play in the background—even if the applet is not displayed in the browser. This is not really a problem, but it can be annoying to the user if the audio clip is looping. The stop method is provided here as a convenience to the user.
Good Programming Practice 18.1
When playing audio clips in an applet or application, provide a mechanism for the user to 
disable the audio.
1 // Fig. 18.6: LoadAudioAndPlay.java
2 // Load an audio clip and play it.
3
4 // Java core packages
5 import java.applet.*;
6import java.awt.*;
7 import java.awt.event.*;
8
9 // Java extension packages
10 import javax.swing.*;
Fig. 18.6 Loading and playing an AudioClip (part 1 of 3).
