import java.applet.*;
import java.awt.*;
import java.awt.image.*;
import java.awt.event.*;
import java.net.*;

public class AnimationProgress extends Applet 
  implements ActionListener{
  Image  []  img;
  int     index = 0;
  int     maxImg;
  boolean working = false;
  Button b;
  MediaTracker tracker;

  public void init() {
    setLayout(new FlowLayout(FlowLayout.LEFT));    
    add(b = new Button("Working"));    
    b.addActionListener(this);
    img = new Image[2];  // 2 images in animation
    maxImg = img.length - 1;
    tracker = new MediaTracker(this);
    try { 
      // images loading
      img[0] = getImage(new URL(getDocumentBase(), "gumby.gif"));
      img[1] = getImage(new URL(getDocumentBase(), "gumby2.gif"));
      tracker.addImage(img[0],0);
      tracker.addImage(img[1],1);
      tracker.waitForAll(); 
      }
    catch (Exception e) {
      e.printStackTrace();
      }

    AnimationThread at = new AnimationThread();
    at.delayedAnimation(this, 500); 
    at.start();
    }

  public void paint(Graphics g) {
    if (img[0] != null) {
       if (working) {
          g.drawImage(img[index],68,0,this);
          index = (index < maxImg) ? index + 1 : 0;
          }
        }
    }

  public void animate() {
    repaint();
    }

  public void actionPerformed(ActionEvent ae) {
    working = !working;
    }

  class AnimationThread extends Thread {
    AnimationProgress  animationApplet;
    int delay; 

    public void delayedAnimation(AnimationProgress a, int delay) {
      this.animationApplet = a;
      this.delay = delay;
      }

    public void run() {
      while (true) {
        try {
          sleep(delay);
          animationApplet.animate();
          } 
        catch (Exception e) {
          e.printStackTrace();
          }
        }
      }
    }
}