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

/**
 * Animation in Java Article Series
 * 
 * Source code provided by Heaton Research, Inc.
 *     http://www.heatonresearch.com/
 * Copyright 2005 by Heaton Research, Inc.
 * 
 * This source code is distributed under a Limited GNU Public
 * License (LGPL).
 * 
 * This is a very basic class to demonstrate the use of the
 * BasicAnimate class. This class shows a white ball that
 * bounces around the applet.
 * 
 * @author Jeff Heaton(http://www.jeffheaton.com)
 * @version 1.0
 */
public class BouncingBall extends BasicAnimate
{
  /**
   * When this class is ran as an application, how wide should it be.
   */   
  public static final int IDEAL_WIDTH = 640;

  /**
   * When this class is ran as an application, how tall should it be.
   */   
  public static final int IDEAL_HEIGHT = 480;

  /**
   * What is the size of the bouncing ball.
   */   
  public final int SIZE = 32;

  /**
   * What is the current x-coordinate of the ball.
   */ 
  private int x = 0;

  /**
   * What is the current y coordinate of the ball. 
   */   
  private int y = 0;

  /**
   * What is the current x-direction of the ball, 1=right, -1=left
   */   
  private int dx = 1;

  /**
   * What is the current y-direction of the ball, 1=down, -1=Up
   */ 
  private int dy = 1;

  /**
   * What is the width of the page that we should check, takes into
   * account how wide the ball is.
   */   
  private int checkWidth;

  /**
   * What is the height of the page that we should check, takes into
   * account how tall the ball is.
   */   
  private int checkHeight;

  /**
   * This method sets up the bouncing ball example.
   *
   */  
  public void init()
  {
    super.init();
    checkWidth = getWidth() - SIZE;
    checkHeight = getHeight() - SIZE;
    setPulseLength(10);
  }

  /**
   * This method renders each frame of the bouncing ball.
   *
   * @param g The off-screen graphics object to paint to.
   */  
  public void paintOffscreen(Graphics g)
  {
    super.paintOffscreen(g);
    x += dx;
    y += dy;
    g.setColor(Color.WHITE);
    g.fillOval(x, y, SIZE, SIZE);

    // bounce if needed
    if ((x > checkWidth) || (x < 0))
      dx = -dx;
    if ((y > checkHeight) || (y < 0))
      dy = -dy;

  }

  /**
   * The main method is called when the class is to be ran
   * as a Java application. This method creates a frame and
   * attaches the applet to the frame. 
   *
   * @param args Not used.
   */  
  public static void main(String args[])
  {
    Applet applet = new BouncingBall();
    Frame frame = new Frame();
    frame.addWindowListener(new WindowAdapter()
    {
      public void windowClosing(WindowEvent e)
      {
        System.exit(0);
      }
    });

    frame.add(applet);
    frame.setSize(IDEAL_WIDTH, IDEAL_HEIGHT);
    frame.show();
    applet.init();
  }
}