JAVA内部类继承如何实现?注意?举例!谢谢!

import java.awt.*;
import java.awt.event.*;
public class TestWindowClose {
public static void main(String args[]) {
new MyFrame55("MyFrame");
}
}
class MyFrame55 extends Frame {
MyFrame55(String s) {
super(s);
setLayout(null);
setBounds(300, 300, 400, 300);
this.setBackground(new Color(204, 204, 255));
setVisible(true);
//this.addWindowListener(new MyWindowMonitor());

this.addWindowListener(
new WindowAdapter() {
public void windowClosing(WindowEvent e) {
setVisible(false);
System.exit(-1);
}
});

}
/*以下是内部类的写法
class MyWindowMonitor extends WindowAdapter {
public void windowClosing(WindowEvent e) {
setVisible(false);
System.exit(0);
}
}
*/
}