funktion på JDialog ok knap

se følgende eks:
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class TestKlasseSwing extends JDialog implements ActionListener, WindowListener
{
      private int frameWidth = 640;
      private int frameHeight = 480;
   
      public TestKlasseSwing()
      {
        createFrame();
      }
   
      private void createFrame()
      {
        setTitle("TestKlasseSwing");
        setResizable(false);
        addWindowListener(this);

        //components
        JButton jb = new JButton("Luk");
        jb.addActionListener(this);
        this.getContentPane().add(jb);

        //Center Frame
        java.awt.Dimension screenSize = java.awt.Toolkit.getDefaultToolkit().getScreenSize();
        setSize(new java.awt.Dimension(frameWidth, frameHeight));
        setLocation( (screenSize.width-this.getWidth()) / 2, (screenSize.height - this.getHeight()) / 2);
      }

      public void windowOpened(WindowEvent e){}
      public void windowClosing(WindowEvent e){ dispose(); System.exit(0);}
      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 void actionPerformed(ActionEvent e)
      {
        dispose();
        System.exit(0);
      }
}

class Main
{
      public static void main(String args[])
      {
        new TestKlasseSwing().show();
      }
}