TrafficLight.java

//Java program for implementing a GUI based Traffic Light with buttons using swing
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class Light extends JPanel implements ActionListener{
    private JRadioButton r1;
    private JRadioButton r2;
    private JRadioButton r3;
    private Color red_c;
    private Color yellow_c;
    private Color green_c;
    Light(){
    setBounds(0,0,640,480);
    r1 = new JRadioButton("Red");
    r2 = new JRadioButton("Yellow");
    r3 = new JRadioButton("Green");
    red_c = getBackground();
    yellow_c = getBackground();
    green_c = getBackground();
    ButtonGroup gp = new ButtonGroup();
    gp.add(r1);
    gp.add(r2);
    gp.add(r3);
    add(r1);
    add(r2);
    add(r3);
    r1.addActionListener(this);
    r2.addActionListener(this);
    r3.addActionListener(this);
}
public void actionPerformed(ActionEvent e){
    if(r1.isSelected() == true){
        red_c = Color.red;
        yellow_c = getBackground();
        green_c = getBackground();
    }
    else if(r2.isSelected() == true){
        red_c = getBackground();
        yellow_c = Color.yellow;
        green_c = getBackground();
    }
    else if(r3.isSelected() == true){
        red_c = getBackground();
        yellow_c = getBackground();
        green_c = Color.green;
    }
    repaint();
}
public void paintComponent(Graphics g){
 super.paintComponent(g);
 g.drawOval(50,50,50,50);
 g.drawOval(50,110,50,50);
 g.drawOval(50,170,50,50);
 g.setColor(red_c);
 g.fillOval(50,50,50,50);
 g.setColor(yellow_c);
 g.fillOval(50,110,50,50);
 g.setColor(green_c);
 g.fillOval(50,170,50,50);
 }
}
class TrafficLight{
    public static void main(String args[]){
     JFrame f = new JFrame();
        f.setVisible(true);
        f.setSize(640,480);
        f.setLayout(null);
        Light t = new Light();
        f.add(t);
    }
}