Animation with colors

[musico]

I am a very novice java programmer. I am doing a basic beginners animation exercise of a ball bouncing around the screen. (copy and paste into your own program)

package ballbounce;

import java.awt.Color;
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.*;


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

class BounceThreadFrame extends JFrame {
public BounceThreadFrame() {
setSize(800, 600);
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();
JLabel lbl = new JLabel("");
p.add(lbl);

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
{
private JLabel lbl;
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);
g.setColor(Color.red);

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(20);
}
} catch (InterruptedException e) {
}


}

private JPanel box;

private static final int frameRate = 60;

private static final int XSIZE = 10;
private static final int YSIZE = 10;
private int x = 100;
private int y = 0;

private int dx = 20;
private int dy = 20;



}

The problem I have is having set the color to a non black (default presumably) it retains each image 'frame' of the ball in a different color (usually turquoisy color) so the screen has a full trail of balls.

How do I prevent this?

Please go easy on me, I am very new to this.

[camickr]

Custom Painting should be done by overring the paintComponent() method of a JPanel (or JComponent), not by using the getGraphics() method. See: Lesson: Performing Custom Painting (The Java™ Tutorials > Creating a GUI With JFC/Swing)

Animation should be done by using a Swing Timer, not by using a Thread. The tutorial also has a section on Timers.

[musico]

Brilliant thanks!

fwiw I did a sort of fix by adding the g.fillOval(x, y, XSIZE, YSIZE) any time a color was changed but I was a bit dubious about the whole animation procedure really. I adapted it from a BallBounce tutorial on the net. It's because I have done a lot of pure data in Java (classes etc.) but using that data to make animation displays is a big step.