Signal Pane Java

 /**
  * Class untuk menggambar Lampu Traffic Light
  */
 import java.awt.*;
 import javax.swing.*;
 class SignalPane extends JPanel{
   Color on;
   int radius = 50;
   int border = 10;
   boolean isOn;
   SignalPane(Color color){
     on = color;
     isOn = false;
   }
   public void turnOn(boolean a){
     isOn = a;
     repaint();
   }
   public Dimension getPreferredSize(){
     int size = (radius+border)*2;
     return new Dimension( size, size );
   }
   protected void paintComponent(Graphics graphics){
     graphics.setColor( Color.black );
     graphics.fillRect(0,0,getWidth(),getHeight());
     if (isOn){
       graphics.setColor( on );
     } else {
       graphics.setColor( on.darker().darker().darker() );
     }
     graphics.fillOval( border,border,2*radius,2*radius );
   }
 }