How to create a bouncing ball

This Java tip shows how to create a bouncing ball animation using threads.

import java.awt.Container;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class BounceThread {
public static void main(String[] args) {
JFrame frame = new BounceThreadFrame();
frame.show();
}
}

class BounceThreadFrame extends JFrame {
public BounceThreadFrame() {
setSize(300, 200);
setTitle("Bounce");

addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});

Container contentPane = getContentPane();
canvas = new JPanel();
contentPane.add(canvas, "Center");
JPanel p = new JPanel();
addButton(p, "Start", new ActionListener() {
public void actionPerformed(ActionEvent evt) {
Ball b = new Ball(canvas);
b.start();
}
});

addButton(p, "Close", new ActionListener() {
public void actionPerformed(ActionEvent evt) {
canvas.setVisible(false);
System.exit(0);
}
});
contentPane.add(p, "South");
}

public void addButton(Container c, String title, ActionListener a) {
JButton b = new JButton(title);
c.add(b);
b.addActionListener(a);
}

private JPanel canvas;
}

class Ball extends Thread {
public Ball(JPanel b) {
box = b;
}

public void draw() {
Graphics g = box.getGraphics();
g.fillOval(x, y, XSIZE, YSIZE);
g.dispose();
}

public void move() {
if (!box.isVisible())
return;
Graphics g = box.getGraphics();
g.setXORMode(box.getBackground());
g.fillOval(x, y, XSIZE, YSIZE);
x += dx;
y += dy;
Dimension d = box.getSize();
if (x < 0) {
x = 0;
dx = -dx;
}
if (x + XSIZE >= d.width) {
x = d.width - XSIZE;
dx = -dx;
}
if (y < 0) {
y = 0;
dy = -dy;
}
if (y + YSIZE >= d.height) {
y = d.height - YSIZE;
dy = -dy;
}
g.fillOval(x, y, XSIZE, YSIZE);
g.dispose();
}

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

private JPanel box;

private static final int XSIZE = 10;

private static final int YSIZE = 10;

private int x = 0;

private int y = 0;

private int dx = 2;

private int dy = 2;
}