bounce.java

this a small java s code

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

public class Bounce
{
  public static void main(String[] args)
  {
    JFrame frame = new BounceFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);
  }
}

class Ball
{
  public void move(Rectangle2D bounds)
  {
    x += dx;
    y += dy;
    if(x<bounds.getMinX())
    {
      x= bounds.getMinX();
      dx =-dx;
    }
    if(x +XSIZE>= bounds.getMaxX())
    {
      x=bounds.getMaxX()- XSIZE;
      dx= -dx;
    }
    if(y<bounds.getMinY())
    {
      y=bounds.getMinY();
      dy = -dy;
    }
    if(y+YSIZE>=bounds.getMaxY())
    {
      y=bounds.getMaxY()- YSIZE;
      dy = -dy;
    }
  }
  
  public Ellipse2D getShape()
  {
    return new Ellipse2D.Double(x,y,XSIZE,YSIZE);
  }
  private static final int XSIZE =15;
  private static final int YSIZE =15;
  private double x=0;
  private double y=0;
  private double dx=1;
  private double dy=1;
}

class BallPanel extends JPanel
{
  public void add(Ball b)
  {
    balls.add(b);
  }
  public void paintComponent(Graphics g)
  {
    super.paintComponent(g);
    Graphics2D g2=(Graphics2D) g;
    for(Ball b: balls)
    {
      g2.fill(b.getShape());
    }
  }
  private ArrayList<Ball> balls = new ArrayList<Ball>();
}

class BounceFrame  extends JFrame
{
  public BounceFrame()
  {
    setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
    setTitle("Bounce");
    
    panel = new BallPanel();
    add(panel,BorderLayout.CENTER);
    JPanel buttonPanel = new JPanel();
    addButton(buttonPanel, "Start",
		new ActionListener()
		{
		  public void actionPerformed(ActionEvent event)
		  {
		    addBall();
		  }
		});
	addButton(buttonPanel, "close",
		new ActionListener()
		{
		  public void actionPerformed(ActionEvent event)
		  {
		    System.exit(0);
		  }
		});
	add(buttonPanel, BorderLayout.SOUTH);
  }
  public void addButton(Container c, String title, ActionListener listener)
  {
    JButton button = new JButton(title);
    c.add(button);
    button.addActionListener(listener);
  }
  public void addBall()
  {
    try
    {
      Ball ball = new Ball();
      panel.add(ball);
      for(int i=1; i<=STEPS; i++)
      {
        ball.move(panel.getBounds());
        panel.paint(panel.getGraphics());
        Thread.sleep(DELAY);
      }
    }
    catch(InterruptedException e)
    {
    
    }  
  }
  private BallPanel panel;
  public static final int DEFAULT_WIDTH=450;
  public static final int DEFAULT_HEIGHT=350;
  public static final int STEPS =10000;
  public static final int DELAY=3;
}