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

public class BallBox1 extends Applet {
        private int x = 7, xChange = 7;
        private int y = 2, yChange = 2;
        private int diameter = 10;
        
        private int LeftX = 0, RightX = 100;
        private int TopY = 0, BottomY = 100;
        
        public void paint(Graphics g) {
            g.drawRect(LeftX, TopY, RightX - LeftX,
                    BottomY - TopY);
            for (int n = 1; n < 100; n++) {
                Color backgroundColor = getBackground();
                g.setColor(backgroundColor);
                g.fillOval(x, y, diameter, diameter);
                if (x <= LeftX) xChange = -xChange;
                if (x >= RightX) xChange = -xChange;
                if (y <= TopY) yChange = -yChange;
                if (y >= BottomY) 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) {
                    System.err.println("sleep exception");
                }
            }
        }
}