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

// This applet animates a circle moving downwards along a diagonal.
// When the circle reaches the bottom, it starts again at the top.

public class CircleApplet extends Applet implements Runnable
{
    int extremity = 0;
    private Thread animator = null;

        // Called when applet page becomes inactive
    public void stop( )
    {
        if( animator != null )
            animator.stop( );
        animator = null;
    }

        // Called when applet page becomes active
    public void start( )
    {
        if( animator == null )
        {
            animator = new Thread( this );
            animator.start( );
        }
    }

        // Implements the Runnable interface
    public void run( )    
    {
        drawCircles( );
    }

        // Infinite loop to draw circle down the main diagonal
        // by calling paint repeatedly
    public void drawCircles( )
    {
        for( ; ; )
            for( extremity = 0; extremity < 200; extremity++ )
            {
                repaint( );
                try
                  { Thread.sleep( 25 ); }
                catch( InterruptedException e ) { }
            }
    }

        // Draw a circle
    public void paint( Graphics g )
    {
        g.fillOval( extremity, extremity, 50, 50 );
    }
}