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

public class MovingBall extends Applet implements Runnable {
    int width, height;
    int r = 30;
    int x, y;
    int moveX = 3, moveY = 3;
    Thread thread;

    AudioClip au;

    int lastPaintedX, lastPaintedY;

    Image off_im;
    Graphics off_g;

    public void init() {
        width = this.size().width;
        height = this.size().height;
        x = r;
        y = height / 2;

        setBackground(Color.blue);
        setForeground(Color.yellow);

        String audiofile = getParameter("audiofile");
        if (audiofile != null) {
            au = getAudioClip(getDocumentBase(), audiofile);
        }

        lastPaintedX = x;
        lastPaintedY = y;

        if (off_g == null) {
            off_im = createImage(width, height);
            off_g = off_im.getGraphics();
            off_g.setColor(getBackground());
            off_g.fillRect(0, 0, width, height);
        }
    }

    public void start() {
        if (thread == null) {
            thread = new Thread(this);
            thread.start();
        }
    }

    public void stop() {
        if (thread != null) {
            thread.stop();
            thread = null;
        }
    }

    public void update(Graphics g) {
        int minX = x < lastPaintedX ? x : lastPaintedX;
        int maxX = x > lastPaintedX ? x : lastPaintedX;
        int minY = y < lastPaintedY ? y : lastPaintedY;
        int maxY = y > lastPaintedY ? y : lastPaintedY;

        off_g.clipRect(minX, minY, maxX - minX + r, maxY - minY + r);
        g.clipRect(minX, minY, maxX - minX + r, maxY - minY + r);

        off_g.setColor(getBackground());
        off_g.fillRect(0, 0, width, height);

        paint(g);
    }

    public void paint(Graphics g) {
        off_g.setColor(getForeground());
        off_g.fillOval(x, y, r, r);

        g.drawImage(off_im, 0, 0, this);

        lastPaintedX = x;
        lastPaintedY = y;
    }

    public void run() {
        while(true) {
            try {
                Thread.sleep(10);
            } catch (InterruptedException e) {
                break;
            }

            x += moveX;
            y += moveY;

            if (x <= 0 || x >= width - r) {
                moveX *= -1;
                au.play();
            }
            if (y <= 0 || y >= height - r) {
                moveY *= -1;
                au.play();
            }

            repaint();
        }
    }
}