3月21日，TestFrame对象是事件源又是监听者，每日20行。

import java.awt.*;import java.awt.event.*;public class TestFrame extends Frame implements WindowListener {    public TestFrame(String s) {        super(s);    }    public void windowClosing(WindowEvent e) {        System.out.println("我退出了！");        e.getWindow().setVisible(false);        ((Window)e.getComponent()).dispose();        System.exit(0);    }    public void windowActivated(WindowEvent e) {}    public void windowClosed(WindowEvent e) {}    public void windowDeactivated(WindowEvent e) {}    public void windowDeiconified(WindowEvent e) {}    public void windowIconified(WindowEvent e) {}    public void windowOpened(WindowEvent e) {}    public static void main(String[] args) {        TestFrame f = new TestFrame("A Test Window");        f.setSize(320, 180);        f.setVisible(true);        f.addWindowListener(f);    }}