// Exercise14_20.java: Create a customizable animation appletimport java.awt.*;import java.awt.event.*;import javax.swing.*;import javax.swing.border.*;import java.net.URL;import java.applet.*;public class Exercise14_20 extends JApplet implements ActionListener {  JTextField jtfSpeed = new JTextField();  JTextField jtfPrefix = new JTextField();  JTextField jtfNumOfImages = new JTextField();  JTextField jtfAudioFile = new JTextField();  JButton jbtStartAnimation = new JButton("Start Animation");  PlayImage playImage = new PlayImage();  Image[] images;  AudioClip audioClip;  int sleepTime;  int numOfImages;  // Initialize the applet  public void init() {    // Panel p to hold animation control    JPanel p = new JPanel();    p.setLayout(new GridLayout(4, 2));    p.add(new JLabel("Animation speed in milliseconds"));    p.add(jtfSpeed);    p.add(new JLabel("Image file prefix"));    p.add(jtfPrefix);    p.add(new JLabel("Number of images"));    p.add(jtfNumOfImages);    p.add(new JLabel("Audio file"));    p.add(jtfAudioFile);    p.setBorder(new TitledBorder(      "Enter information for animation"));    // Panel jpButton to hold the button    JPanel jpButton = new JPanel();    jpButton.setLayout(new FlowLayout(FlowLayout.RIGHT));    jpButton.add(jbtStartAnimation);    // Add the button, image panel, and panel p to the applet    getContentPane().add(jpButton, BorderLayout.NORTH);    getContentPane().add(playImage, BorderLayout.CENTER);    getContentPane().add(p, BorderLayout.SOUTH);    // Register listener    jbtStartAnimation.addActionListener(this);  }  // Handle button action  public void actionPerformed(ActionEvent e) {    startAnimation();  }  public void startAnimation() {    MediaTracker imageTracker = new MediaTracker(this);    // Obtain a Toolkit instance    Toolkit toolkit = Toolkit.getDefaultToolkit();    URL url = null;    String prefix = jtfPrefix.getText().trim();    numOfImages =      new Integer(jtfNumOfImages.getText().trim()).intValue();    String audioFile = jtfAudioFile.getText().trim();    sleepTime = new Integer(jtfSpeed.getText().trim()).intValue();    // Load the image, the image files are named    // L1 - L52 in Images directory    images = new Image[numOfImages];    for (int i=0; i<images.length; i++) {      // Get the URL for the file name      url = this.getClass().getResource("image/" + prefix + (i+1)        + ".gif");      images[i] = toolkit.getImage(url);      // Register images with the imageTracker      imageTracker.addImage(images[i], i);    }    // Play a sound    try {      url = this.getClass().getResource(audioFile);    }    catch (Exception ex) {      System.out.println(ex);    }    System.out.println("url = " + url);    audioClip = Applet.newAudioClip(url);    // Wait for all the images to be completely loaded    try {      imageTracker.waitForAll();    }    catch (InterruptedException ex) {      System.out.println(ex);    }    // Dispose of imageTracker and audioClip since they are no longer needed    imageTracker = null;    // Start image animation    playImage.beginAnimation();  }  // Main method  public static void main(String[] args) {    // Create a frame    JFrame frame = new JFrame("Exercise14_20");    // Create an instance of the applet    Exercise14_20 applet = new Exercise14_20();    // Add the applet instance to the frame    frame.getContentPane().add(applet, BorderLayout.CENTER);    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    // Invoke init() and start()    applet.init();    applet.start();    // Display the frame    frame.setSize(500, 400);    frame.setVisible(true);  }  class PlayImage extends JPanel implements Runnable {    private Thread thread = null;    int currentImageIndex = 0;    Image imageToDisplay;    // Determine the thread status    protected boolean suspended = false;    // Constructor    public PlayImage() {      // Start with the first image      currentImageIndex = 0;      thread = new Thread(this);      setBorder(new LineBorder(Color.red, 1));    }    public void beginAnimation() {      thread.start();      if (audioClip != null) audioClip.loop();    }    public void start() {      resume();    }    public void stop() {      suspend();    }    public synchronized void resume() {      if (suspended) {        suspended = false;        notify();      }    }    public synchronized void suspend() {      suspended = true;    }    public void destroy() {      thread = null;    }    public void run() {      while (true) {        imageToDisplay =          images[currentImageIndex%numOfImages];        // Make sure currentImageIndex is nonnegative        if (currentImageIndex == 0) currentImageIndex = 52;        currentImageIndex = currentImageIndex + 1;        repaint();        try {          thread.sleep(sleepTime);          synchronized (this) {            while (suspended)              wait();          }        }        catch (InterruptedException ex) {        }      }    }    // Display an image    public void paintComponent(Graphics g) {      super.paintComponent(g);      if (imageToDisplay != null) {        g.drawImage(imageToDisplay, 0, 0, getSize().width,          getSize().height, this);      }    }  }}