Multiple Independent Animations

import java.awt.*;
import java.applet.*;

public class TwoBall extends Applet implements Runnable {

  Ball b1, b2;
  Thread t;
  
  public void init () {
  
    b1 = new Ball(10, 32, size());
    b1.start();
    b2 = new Ball(155, 75, size());
    b2.start();
    t = new Thread(this);
    t.start();
     
  }
  
  
  public void paint (Graphics g) {
    g.fillOval(b1.getX(), b1.getY(), b1.getWidth(), b1.getHeight());
    g.fillOval(b2.getX(), b2.getY(), b2.getWidth(), b2.getHeight());
  }
  
  public void run() {

    Thread.currentThread().setPriority(Thread.MIN_PRIORITY);

    while (true) {  // infinite loop
      this.repaint();
      try {
        Thread.sleep(10);
      }
      catch (InterruptedException e) {      
      }
    }
    
  }


}

class Ball extends Thread {

  private Rectangle r;
  private int x_increment = 1;
  private int deltaY = 1;
  private Dimension bounds;

  public Ball(int x, int y, Dimension d) {
    r = new Rectangle(x, y, 20, 20);
    bounds = d;
  }

  public int getX() {
    return r.x;
  }

  public int getY() {
    return r.y;
  }

  public int getHeight() {
    return r.height;
  }

  public int getWidth() {
    return r.width;
  }

  public void run() {

    Thread.currentThread().setPriority(Thread.MIN_PRIORITY);

    while (true) {  // infinite loop
      r.x += deltaX;
      r.y += deltaY;
      if (r.x + r.width >= bounds.width || r.x < 0) {
        deltaX *= -1;
      }
      if (r.y + r.height >= bounds.height || r.y < 0) {   
        deltaY *= -1;
      }
      try {
        Thread.sleep(30);
      }
      catch (InterruptedException e) {   
      }
      
    }
    
  }

}