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

import java.awt.FlowLayout;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import java.awt.event.ItemListener;
import java.awt.event.ItemEvent;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JCheckBox;

public class JavaCircle extends JFrame {
    private final JCheckBox red;
    private final JCheckBox green;
    private final JCheckBox blue;
    private Graphics g;

    public JavaCircle() {
        super("Changing the color of a circle");
        setLayout(new FlowLayout());
        red = new JCheckBox("Red");
        add(red);
        green = new JCheckBox("Green");
        add(green);
        blue = new JCheckBox("Blue");
        add(blue);



        CheckBoxHandler handler = new CheckBoxHandler();
        red.addItemListener(handler);
        green.addItemListener(handler);
        blue.addItemListener(handler);

    }

    public void paint(Graphics g) {
        g.drawOval(480, 480, 200, 200);
        g.fillOval(480, 480, 200, 200);
        g.setColor(Color.BLACK);
    }

    private class CheckBoxHandler implements ItemListener {
        public void itemStateChanged(ItemEvent event) {
            if (red.isSelected()) {
                paint(null);
                g.drawOval(480, 480, 200, 200);
                g.fillOval(480, 480, 200, 200);
                g.setColor(Color.RED);
            } else if (green.isSelected()) {
                g.setColor(Color.GREEN);
                g.drawOval(480, 480, 200, 200);
                g.fillOval(480, 480, 200, 200);
            } else if (blue.isSelected()) {
                g.setColor(Color.BLUE);
                g.drawOval(480, 480, 200, 200);
                g.fillOval(480, 480, 200, 200);
            }
        }
    }

    public static void main(String args[]) {
        JavaCircle t = new JavaCircle();
        t.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        t.setSize(500, 500);
        t.setVisible(true);
    }
}