// This now has a delay
// because modern machines make the ball go too fast.
// The delay is done using Thread.sleep
// which is explained in the chapter on threads

import java.awt.*;
import java.applet.Applet;

public class Ball extends Applet {

    private int x = 7, xChange = 7;
    private int y = 2, yChange = 2;
    private int diameter = 10;

    private int rectLeftX = 0, rectRightX = 100;
    private int rectTopY = 0, rectBottomY = 100;

    public void paint(Graphics g) {
        g.drawRect(rectLeftX, rectTopY,
                   rectRightX-rectLeftX, rectBottomY-rectTopY);

        for (int n = 1; n < 100; n++) {

            Color backgroundColour = getBackground();
            g.setColor(backgroundColour);
            g.fillOval(x, y, diameter, diameter);

            if(x <= rectLeftX) xChange = -xChange;
            if(x >= rectRightX) xChange = -xChange;

            if(y <= rectTopY) yChange = -yChange;
            if(y >= rectBottomY) yChange = -yChange;

            x = x + xChange;
            y = y + yChange;

            g.setColor(Color.red);
            g.fillOval(x, y, diameter, diameter);

            try {
                Thread.sleep(50);
            }
            catch (InterruptedException e) {
                return;
            }
        }
    }
}