import java.awt.Color;
import java.awt.Graphics;

public class SignalControlApplet extends Applet implements Runnable {

	int x=-1;
	Thread t;
	Graphics g;
	public void init()
	{
		g=getGraphics();
		t=new Thread(this);
		t.start();
	}
	public void run()
	{
		while(true)
		{
			x=x+1;
			g.setColor(Color.white);
			g.fillRect(0,0,600,600);
			switch(x)
			{
				case 0:g.setColor(Color.red);
					g.fillOval(50,50,100,100);
					g.setColor(Color.black);
					g.fillOval(50,160,100,100);
					g.fillOval(50,270,100,100);
					break;
				case 1:g.setColor(Color.black);
					g.fillOval(50,50,100,100);
					g.setColor(Color.yellow);
					g.fillOval(50,160,100,100);
					g.setColor(Color.black);
					g.fillOval(50,270,100,100);
					break;
				case 2:g.setColor(Color.black);
					g.fillOval(50,50,100,100);
					g.fillOval(50,160,100,100);
					g.setColor(Color.green);
					g.fillOval(50,270,100,100);
					x=-1;
					break;
			}
			try
			{
				Thread.sleep(500);
			}catch(Exception ee){}
		}
	}
}
/*
 <applet height=600 width=600 code=SignalControlApplet>
 </applet>
*/