package bouncingball;

import java.awt.*;
import java.awt.event.*;
import java.applet.*;
import javax.swing.*;

public class Applet1 extends  Applet implements ActionListener {

  private Balls ball;
  private Button start, stop;

  public void init() {
    start = new Button("Start");
    add(start);
    start.addActionListener(this);

    stop = new Button("Stop");
    add(stop);
    stop.addActionListener(this);
  }
  public void actionPerformed(ActionEvent event)  {
    if(event.getSource() == start)  {
      Graphics g = getGraphics();
      ball =  new Balls(g);
      ball.start();
  }
   if(event.getSource() == stop)
     ball.pleaseStop();
  }
}
 class Balls extends Thread  {
  boolean keepGoing;
  private Graphics g;
  private int x = 45, xChange = 20;
  private int y = 42, yChange = 15;
  private int diameter = 12;
  private int rectLeftX = 20, rectRightX = 285;
  private int rectTopY = 40, rectBottomY = 280;

  public Balls (Graphics graphics) {
  g = graphics;
  keepGoing = true;
  }
  public void pleaseStop()  {
  keepGoing = false;
  }

  public void run()  {
  g.setColor(Color.white);
  g.fillRect( rectLeftX, rectTopY,
       rectRightX - rectLeftX, rectBottomY - rectTopY);
  g.setColor(Color.black);
  g.drawRect( rectLeftX, rectTopY,
       rectRightX - rectLeftX, rectBottomY - rectTopY);
  while(keepGoing)  {
  g.setColor(Color.white);
  g.fillOval(x, y, diameter, diameter);

  if ( x + xChange <= rectLeftX)
    xChange = -xChange;

  if ( x + xChange >= rectRightX)
    xChange = -xChange;

  if (y + yChange <= rectTopY)
    yChange = -yChange;

  if (y + yChange >= rectBottomY)
    yChange = -yChange;

  x += xChange;
  y += yChange;

  g.setColor(Color.red);
  g.fillOval(x, y, diameter, diameter);

  try   {
    Thread.sleep(60);
  }
  catch (InterruptedException e)  {
     System.err.println("sleep exception");
  }
 }
 }
}