import javax.swing.JFrame;
public class TrafficLight
{
    //----------------------------------------------
// Creates the main program frame.
//----------------------------------------------
public static void main(String[] args)
{
JFrame frame = new JFrame("Traffic Light");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new TrafficControlPanel());
frame.pack();
frame.setVisible(true);
    }
}
//**********************************************************************************
//**********************************************************************************
//**********************************************************************************

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class TrafficControlPanel extends JPanel
{
    private JButton switchLight;
    TrafficLightPanel lightPanel = new TrafficLightPanel();
public TrafficControlPanel()
{
switchLight = new JButton("Change Light");
switchLight.addActionListener(new ChangeListener());
add(lightPanel, BorderLayout.CENTER);
add(switchLight, BorderLayout.SOUTH);
}
private class ChangeListener implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
    lightPanel.change();
}
}
}
//**********************************************************************************
//**********************************************************************************
//**********************************************************************************


//********************************************************************
//  TrafficLightPanel.java
//********************************************************************
import javax.swing.*;
import java.awt.*;
public class TrafficLightPanel extends JPanel
{
private int currentState = 0;
private final int NUM_LIGHTS = 3; // the number of lights
private final int X = 50, Y = 10, WIDTH = 50, HEIGHT = 130; //box
//size
private final int DIAMETER = 30; // light diameter
private final int X_OFFSET = 10, Y_OFFSET = 10; // offsets to
//position the lights in the box
private final int PANEL_WIDTH = 150, PANEL_HEIGHT = 230; // the size
//of a traffic control panel
   //-----------------------------------------------------------------
   //  Creates the traffic light panel
   //-----------------------------------------------------------------
public TrafficLightPanel()
{
      setPreferredSize(new Dimension(PANEL_WIDTH, PANEL_HEIGHT));
   }
public void paintComponent(Graphics page)
{
      super.paintComponent(page);
int lightOn = currentState % NUM_LIGHTS;
setBackground(Color.white);
page.setColor(Color.lightGray);
page.fillRect(X, Y, WIDTH, HEIGHT);
// add code to determine the light to turn on and turn on the
//light
if (lightOn == 0)
{
    page.setColor(Color.red);
    page.fillOval(X + X_OFFSET, Y + Y_OFFSET, DIAMETER, DIAMETER);
    page.setColor(Color.darkGray);
    page.fillOval(X + X_OFFSET, Y + (2 * Y_OFFSET) + DIAMETER,
            DIAMETER, DIAMETER);
    page.fillOval(X + X_OFFSET, Y + (3 * Y_OFFSET) + (2 * DIAMETER),
            DIAMETER, DIAMETER);
}
if (lightOn == 1)
{
    page.setColor(Color.green);
    page.fillOval(X + X_OFFSET, Y + (3 * Y_OFFSET) + (2 * DIAMETER),
            DIAMETER, DIAMETER);
    page.setColor(Color.darkGray);
    page.fillOval(X + X_OFFSET, Y + Y_OFFSET, DIAMETER, DIAMETER);
    page.fillOval(X + X_OFFSET, Y + (2 * Y_OFFSET) + DIAMETER,
            DIAMETER, DIAMETER);
}
if (lightOn == 2)
{
    page.setColor(Color.yellow);
    page.fillOval(X + X_OFFSET, Y + (2 * Y_OFFSET) + DIAMETER,
            DIAMETER, DIAMETER);
    page.setColor(Color.darkGray);
    page.fillOval(X + X_OFFSET, Y + Y_OFFSET, DIAMETER, DIAMETER);
    page.fillOval(X + X_OFFSET, Y + (3 * Y_OFFSET) + (2 * DIAMETER),
            DIAMETER, DIAMETER);
}
}
public void change()
{
      currentState++;
repaint();
   }
}
//**********************************************************************************
//**********************************************************************************
//**********************************************************************************