[hardwired]

Code:

//  <applet code="OkAnimation" width="300" height="300"></applet>
//  use: >appletviewer OkAnimation.java
import java.applet.*;
import java.awt.*;

public class OkAnimation extends Applet implements Runnable
{
    int y;
    int dy = 10;
    Thread t = null;
    boolean isRunning = false;

    /** Applet method override */
    public void paint(Graphics g)
    {
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        g.fillOval(100, y, 50, 50);
    }

    /** Applet method override */
    public void start()
    {
        if(!isRunning)
        {
            isRunning = true;
            t = new Thread(this);
            t.start();
        }
    }

    /** Applet method override */
    public void stop()
    {
        isRunning = false;
        if(t != null)
            t.interrupt();  // wake up
        t = null;
    }

    /** Runnable interface implementation */
    public void run()
    {
        while(isRunning)
        {
            try
            {
                t.sleep( 1000 );
            }
            catch(InterruptedException e)
            {
                stop();
            }
            if(y + dy < 0 || y + 50 + dy > getHeight()) {
                // if the next move puts us out of bounds
                // reverse direction.
                dy *= -1;
            }
            y = y+dy;
            repaint();
        }
    }
}