import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
class Signal extends JPanel{
Color on;
int radius = 40;
int border = 10;
boolean change;
Signal(Color color){
on = color;
change = true;
}
public void turnOn(boolean a){
change = a;
repaint();
}
public Dimension getPreferredSize(){
int size = (radius+border)*2;
return new Dimension( size, size );
}
public void paintComponent(Graphics graphics){
graphics.setColor( Color.black );
graphics.fillRect(0,0,getWidth(),getHeight());
if (change){
graphics.setColor( on );
} else {
graphics.setColor( on.darker().darker().darker() );
}
graphics.fillOval( border,border,2*radius,2*radius );
}
}