Swing :- Warning Option Program

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

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

private JButton buttonOK;
private JTextField textName;

public Salutation()
{
   this.setSize(325,100);
   this.setTitle("Identify yourself");
   this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

ButtonListener bl = new ButtonListener();

   JPanel panel1 = new JPanel();

panel1.add(new JLabel("Enter your name: "));

textName = new JTextField(15);
panel1.add(textName);

buttonOK = new JButton("OK");
buttonOK.addActionListener(bl);
   panel1.add(buttonOK);

   this.add(panel1);

   this.setVisible(true);
}

private class ButtonListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
if (e.getSource() == buttonOK)
{
String name = textName.getText();
if (name.length() == 0)
{
JOptionPane.showMessageDialog(Salutation.this,
   "Please don't leave the box empty!",
   "Empty!!",
   JOptionPane.INFORMATION_MESSAGE);
}
else
{
JOptionPane.showMessageDialog(Salutation.this,
   "Good morning " + textName.getText(),
   "Greetings to you",
   JOptionPane.INFORMATION_MESSAGE);
}
textName.requestFocus();
}
}
}
}