关闭窗口问题

下面的代码，本来没有实现关闭窗口的的，但我想实现，为什么加了addWindowListener(new WindowAdapter()的关闭窗口代码进去还是无法关闭的，请大家指教一下小弟，感激不尽～


/*使用内部类处理鼠标移动事件和鼠标事件*/

import java.awt.*;
import java.awt.event.*;
import java.util.*;
 public class TowListenIner extends Frame implements ActionListener{
    private Frame f;
    private TextField tf;
    public TowListenIner(){
        addWindowListener(new WindowAdapter(){
            public void windowClosing(WindowEvent e){
                dispose();
                System.exit(0);
            }
        });
    }
    public void actionPerformed(ActionEvent e){};
    public static void main(String[] args){
        TowListenIner that = new TowListenIner();
        that.go();
    }
    public void go(){
        f= new Frame("两个监听者的例子");
        f.add("North",new Label("Click and drag the mouse"));
        tf = new TextField(30);
        f.add("South",tf);
        f.addMouseMotionListener(new MouseMotionHandler());
        f.addMouseListener(new MouseEventHandler());
        f.setSize(300,300);
        f.setVisible(true);
    }
    public class MouseMotionHandler extends MouseMotionAdapter{
        public void mouseDragged(MouseEvent e){
            String s = "鼠标的拖动位置:X="+e.getX()+"Y="+e.getY();
            tf.setText(s);
        }
    }
    public class MouseEventHandler extends MouseAdapter{
        public void mouseEntered(MouseEvent e){
            String s = "鼠标进来";
            tf.setText(s);
        }
        public void mouseExited(MouseEvent e){
            String s= "鼠标离开";
            tf.setText(s);
        }
    }
    
    
}