Learning Java, 4th Edition

Simple Audio

Now we’ll turn from images and open our ears to audio. Java Sound API provides fine-grained support for the creation and manipulation of both sampled audio and MIDI music, as well as control over MIDI devices. There’s space here only to scratch the surface by examining how to play simple sampled sound and MIDI music files. With the standard Java Sound support bundled with Java, you can play a wide range of file formats including AIFF, AU, Windows WAV, standard MIDI files, and Rich Music Format (RMF) files. We’ll discuss other formats (such as MP3) along with video media in the next section.

java.applet.AudioClip defines the simplest interface for objects that can play sound. An object that implements AudioClip can be told to play() its sound data, stop() playing the sound, or loop() continuously.

The Applet class provides a handy static method, newAudioClip(), that retrieves sounds from files or over the network. (And there is no reason we can’t use it in a non-applet application.) The method takes an absolute or relative URL to specify where the audio file is located and returns an AudioClip. The following application, NoisyButton, gives a simple example:

    //file: NoisyButton.java
    import java.applet.*;
    import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;

    public class NoisyButton {

      public static void main(String[] args) throws Exception {
        JFrame frame = new JFrame("NoisyButton");
        java.io.File file = new java.io.File( args[0] );
        final AudioClip sound = Applet.newAudioClip(file.toURL());

        JButton button = new JButton("Woof!");
        button.addActionListener(new ActionListener() {
          public void actionPerformed(ActionEvent e) { sound.play(); }
        });

        Container content = frame.getContentPane();
        content.setBackground(Color.pink);
        content.setLayout(new GridBagLayout());
        content.add(button);
        frame.setVisible(true);
        frame.setSize(200, 200);
        frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        frame.setVisible(true);
      }
    }

Run NoisyButton, passing the name of the audio file you wish to use as the argument. (We’ve supplied one called bark.aiff.)

NoisyButton retrieves the AudioClip using a File and the toURL()method to reference it as a URL. When the button is pushed, we call the play() method of the AudioClip to start things. After that, it plays to completion unless we call the stop() method to interrupt it.

This interface is simple, but there is a lot of machinery behind the scenes. Next, we’ll look at the Java Media Framework, which supports a wider range of media types.