import javax.swing.*;
import java.awt.event.*;

class WindowHandler implements WindowListener {
    private JFrame frame;

    public WindowHandler(JFrame frame) {
        this.frame = frame;
    }

    // this is called when the user tries to close the window
    public void windowClosing(WindowEvent e) {
        int choice = JOptionPane.showConfirmDialog(null, "Are you sure you want to quit?",
                "Really Quit?", JOptionPane.YES_NO_OPTION);

        if (choice == JOptionPane.YES_OPTION) {
            frame.dispose();
        }
    }

    // we must override all of these methods to implement the interface, but don't care about them
    public void windowOpened(WindowEvent e) {}
    public void windowClosed(WindowEvent e) {}
    public void windowIconified(WindowEvent e) {}
    public void windowDeiconified(WindowEvent e) {}
    public void windowActivated(WindowEvent e) {}
    public void windowDeactivated(WindowEvent e) {}
}

public class ReallyQuit {
    public static void main(String[] args) {
        // create and set up the window.
        JFrame frame = new JFrame("Button Example!");

        // make the program close when the window closes
        frame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
        frame.addWindowListener(new WindowHandler(frame));

        // add a button object
        JButton button = new JButton("Push Me!");
        frame.getContentPane().add(button);

        // display the window.
        frame.pack();
        frame.setVisible(true);
    }
}