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

public class MovingBall extends Applet implements Runnable
{
    int x_pos = 10;
    int y_pos = 100;
    int x_speed = 1;
    int radius = 20;
    private Image dbImage;
    private Graphics dbg;
    int appletsize_x = 300;
    int appletsize_y = 300;

public void init() {
    setBackground (Color.blue);
}

public void start() {
    Thread th = new Thread(this);
    th.start();
}

public void stop() { }

public void destroy() { }

public void run () {
    Thread.currentThread().setPriority(Thread.MIN_PRIORITY);

    while (true)
    {
        x_pos += x_speed;
        if (x_pos > appletsize_x - (radius * 6))
        {
        x_speed = -1;
        }
        else if (x_pos < radius)
        {

        x_speed = +1;
        }


    repaint();

    try
    {

    Thread.sleep (20);
    }
    catch (InterruptedException ex)
    {

    }


    Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
    }
}

public void paint (Graphics g) {

    g.setColor (Color.red);


    g.fillOval (x_pos - radius, y_pos - radius, 2 * radius, 2 * radius);
}
public void update(Graphics g){

    if (dbImage == null)
    {
    dbImage = createImage (this.getSize().width, this.getSize().height);
    dbg = dbImage.getGraphics ();
    }


    dbg.setColor (getBackground ());
    dbg.fillRect (0, 0, this.getSize().width, this.getSize().height);


    dbg.setColor (getForeground());
    paint (dbg);


    g.drawImage (dbImage, 0, 0, this);
}

}