Swing Button:- Click Magic Program

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

public class ClickMe extends JFrame
{
public static void main(String [] args)
{
new ClickMe();
}

private JButton button1, exitButton;

public ClickMe()
{
   this.setSize(275,100);
   this.setTitle("I am counting!!");
   this.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);

ClickListener cl = new ClickListener();

   JPanel panel1 = new JPanel();

   addWindowListener(new WindowAdapter()
    {
public void windowClosing(WindowEvent e)
{
exitButton.doClick();
}
} );

button1 = new JButton("Press Enter or Click Mouse!");
button1.setMnemonic('P');
getRootPane().setDefaultButton(button1);
button1.addActionListener(cl);
   panel1.add(button1);

   exitButton = new JButton("EXIT");
   exitButton.addActionListener(cl);
   panel1.add(exitButton);

   this.add(panel1);

   this.setVisible(true);
}

private class ClickListener implements ActionListener
{
private int clickCount = 0;

public void actionPerformed(ActionEvent e)
{
if (e.getSource() == button1)
{
clickCount++;
if (clickCount == 1)
button1.setText("You clicked Me!");
   else
button1.setText("You clicked "
+ clickCount + " times!");
}
else if (e.getSource() == exitButton)
{
if (clickCount > 0)
System.exit(0);
else
{
JOptionPane.showMessageDialog(ClickMe.this,
   "...try clicking once!!",
   "In a hurry...!!",
   JOptionPane.ERROR_MESSAGE);
}
}
}
}
}