Loading and Playing Audio Clips
Java programs can manipulate and play audio clips. Users can capture their own audio clips, and many clips are available in software products and over the Internet. Your system needs to be equipped with audio hardware (speakers and a sound card) to be able to play the audio clips.
Java provides several mechanisms for playing sounds in an applet. The two simplest are the Applet's play method and the play method of the AudioClip interface. Additional audio capabilities are available in the Java Media Framework and Java Sound APIs. If you would like to play a sound once in a program, the Applet method play loads the sound and plays it oncethe sound is marked for garbage collection after it plays. The Applet method play has two versions:
public void play( URL location, String soundFileName ); public void play( URL soundURL );
The first version loads the audio clip stored in file soundFileName from location and plays the sound. The first argument is normally a call to the applet's getdocumentBase or getCodeBase method. Method geTDocumentBase returns the location of the HTML file that loaded the applet. (If the applet is in a package, the method returns the location of the package or the 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 the clip 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 extensions) 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. 21.5 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 a program's execution.
Figure 21.5. Loading and playing an AudioClip.
(This item is displayed on pages 991 - 992 in the print version)
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1 // Fig. 21.5: LoadAudioAndPlay.java 2 // Load an audio clip and play it. 3 import java.applet.AudioClip; 4 import java.awt.event.ItemListener; 5 import java.awt.event.ItemEvent; 6 import java.awt.event.ActionListener; 7 import java.awt.event.ActionEvent; 8 import java.awt.FlowLayout; 9 import javax.swing.JApplet; 10 import javax.swing.JButton; 11 import javax.swing.JComboBox; 12 13 public class LoadAudioAndPlay extends JApplet 14 { 15 private AudioClip sound1, sound2, currentSound; 16 private JButton playJButton, loopJButton, stopJButton; 17 private JComboBox soundJComboBox; 18 19 // load the image when the applet begins executing 20 public void init() 21 { 22 setLayout( new FlowLayout() ); 23 24 String choices[] = { "Welcome", "Hi" }; 25 soundJComboBox = new JComboBox( choices ); // create JComboBox 26 27 soundJComboBox.addItemListener( 28 29 new ItemListener() // anonymous inner class 30 { 31 // stop sound and change to sound to user's selection 32 public void itemStateChanged( ItemEvent e ) 33 { 34 currentSound.stop(); 35 currentSound = soundJComboBox.getSelectedIndex() == 0 ? 36 sound1 : sound2; 37 } // end method itemStateChanged 38 } // end anonymous inner class 39 ); // end addItemListener method call 40 41 add( soundJComboBox ); // add JComboBox to applet 42 43 // set up button event handler and buttons 44 ButtonHandler handler = new ButtonHandler(); 45 46 // create Play JButton 47 playJButton = new JButton( "Play" ); 48 playJButton.addActionListener( handler ); 49 add( playJButton ); 50 51 // create Loop JButton 52 loopJButton = new JButton( "Loop" ); 53 loopJButton.addActionListener( handler ); 54 add( loopJButton ); 55 56 // create Stop JButton 57 stopJButton = new JButton( "Stop" ); 58 stopJButton.addActionListener( handler ); 59 add( stopJButton ); 60 61 // load sounds and set currentSound 62 sound1 = getAudioClip( getDocumentBase(), "welcome.wav" ); 63 sound2 = getAudioClip( getDocumentBase(), "hi.au" ); 64 currentSound = sound1; 65 } // end method init 66 67 // stop the sound when the user switches Web pages 68 public void stop() 69 { 70 currentSound.stop(); // stop AudioClip 71 } // end method stop 72 73 // private inner class to handle button events 74 private class ButtonHandler implements ActionListener 75 { 76 // process play, loop and stop button events 77 public void actionPerformed( ActionEvent actionEvent ) 78 { 79 if ( actionEvent.getSource() == playJButton ) 80 currentSound.play(); // play AudioClip once 81 else if ( actionEvent.getSource() == loopJButton ) 82 currentSound.loop(); // play AudioClip continuously 83 else if ( actionEvent.getSource() == stopJButton ) 84 currentSound.stop(); // stop AudioClip 85 } // end method actionPerformed 86 } // end class ButtonHandler 87 } // end class LoadAudioAndPlay |
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 methodsplay, loop and stop. As mentioned earlier, method play plays the audio clip once. Method loop continuously loops through 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 6263 in the applet's init method use getAudioClip to load two audio filesa Windows Wave file (welcome.wav) and a Sun Audio file (hi.au). The user can select which audio clip to play from the JComboBox soundJComboBox. Note that the applet's stop method is overridden at lines 6871. 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, it continues to play in the backgroundeven if the applet is not displayed in the browser. This is not necessarily 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.
Look-and-Feel Observation 21.5
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When playing audio clips in an applet or application, provide a mechanism for the user to disable the audio. |