窗口关闭事件

import java.awt.*;
import java.awt.event.*;

public class app16_3 extends Frame implements ActionListener
{
	static app16_3 frm=new app16_3();
	static Button btn1=new Button("yellow");
	static Button btn2=new Button("green");
	static Button btn3=new Button("exit");

	public static void main(String args[]){
	    
		btn1.addActionListener(frm);
		btn2.addActionListener(frm);
		btn3.addActionListener(frm);

		frm.setTitle("Action Event");
		frm.setLayout(new FlowLayout(FlowLayout.CENTER));
		frm.setSize(200,150);
		frm.add(btn1);
		frm.add(btn2);
		frm.add(btn3);
		frm.setVisible(true);
	}

	public void actionPerformed(ActionEvent e){
	  
	    Button btn=(Button)e.getSource();
		if(btn==btn1)
		frm.setBackground(Color.yellow);
        else if(btn==btn2)
	    frm.setBackground(Color.green);
		else
		System.exit(0);
	}
}