/**
   @version 1.30 2001-05-06
   @author Cay Horstmann
*/

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
import javax.swing.*;

/**
   Shows an animated bouncing ball running in a separate thread
*/
public class BounceThread
{
   public static void main(String[] args)
   {
      JFrame frame = new BounceFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.show();
   }
}

/**
   The frame with canvas and buttons.
*/
class BounceFrame extends JFrame
{
   /**
      Constructs the frame with the canvas for showing the
      bouncing ball and Start and Close buttons
   */
   public BounceFrame()
   {
      setSize(WIDTH, HEIGHT);
      setTitle("BounceThread");

      Container contentPane = getContentPane();
      canvas = new BallCanvas();
      contentPane.add(canvas, BorderLayout.CENTER);
      JPanel buttonPanel = new JPanel();
      addButton(buttonPanel, "Start",
         new ActionListener()
            {  
               public void actionPerformed(ActionEvent evt)
               {
                  addBall();
               }
            });

      addButton(buttonPanel, "Close",
         new ActionListener()
            {
               public void actionPerformed(ActionEvent evt)
               {
                  System.exit(0);
               }
            });
      contentPane.add(buttonPanel, BorderLayout.SOUTH);
   }

   /**
      Adds a button to a container.
      @param c the container
      @param title the button title
      @param listener the action listener for the button
   */
   public void addButton(Container c, String title,
      ActionListener listener)
   {
      JButton button = new JButton(title);
      c.add(button);
      button.addActionListener(listener);
   }

   /**
      Adds a bouncing ball to the canvas and starts a thread
      to make it bounce
   */
   public void addBall()
   {
      Ball b = new Ball(canvas);
      canvas.add(b);
      BallThread thread = new BallThread(b);
      thread.start();
   }

   private BallCanvas canvas;
   public static final int WIDTH = 450;
   public static final int HEIGHT = 350;  
}

/**
   A thread that animates a bouncing ball.
*/
class BallThread extends Thread
{
   /**
      Constructs the thread.
      @aBall the ball to bounce
   */
   public BallThread(Ball aBall) { b = aBall; }

   public void run()
   {
      try
      {
         for (int i = 1; i <= 1000; i++)
         {
            b.move();
            sleep(5);
         }
      }
      catch (InterruptedException exception)
      {                    
      }
   }

   private Ball b;
}

/**
   The canvas that draws the balls.
*/
class BallCanvas extends JPanel
{
   /**
      Add a ball to the canvas.
      @param b the ball to add
   */
   public void add(Ball b)
   {
      balls.add(b);
   }

   public void paintComponent(Graphics g)
   {
      super.paintComponent(g);
      Graphics2D g2 = (Graphics2D)g;
      for (int i = 0; i < balls.size(); i++)
      {
         Ball b = (Ball)balls.get(i);
         b.draw(g2);
      }     
   }

   private ArrayList balls = new ArrayList();
}

/**
   A ball that moves and bounces off the edges of a 
   component
*/
class Ball
{
   /**
      Constructs a ball in the upper left corner
      @c the component in which the ball bounces
   */
   public Ball(Component c) { canvas = c; }

   /**
      Draws the ball at its current position
      @param g2 the graphics context
   */
   public void draw(Graphics2D g2)
   {
      g2.fill(new Ellipse2D.Double(x, y, XSIZE, YSIZE));
   }

   /**
      Moves the ball to the next position, reversing direction
      if it hits one of the edges
   */
   public void move()
   {
      x += dx;
      y += dy;
      if (x < 0)
      { 
         x = 0;
         dx = -dx;
      }
      if (x + XSIZE >= canvas.getWidth())
      {
         x = canvas.getWidth() - XSIZE; 
         dx = -dx; 
      }
      if (y < 0)
      {
         y = 0; 
         dy = -dy;
      }
      if (y + YSIZE >= canvas.getHeight())
      {
         y = canvas.getHeight() - YSIZE;
         dy = -dy; 
      }

      canvas.repaint();
   }

   private Component canvas;
   private static final int XSIZE = 15;
   private static final int YSIZE = 15;
   private int x = 0;
   private int y = 0;
   private int dx = 2;
   private int dy = 2;
}