关于事件处理的问题按钮窗口关闭但是按了没反应

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.event.*;

import javax.swing.*;

class AFramee extends JFrame{
public AFramee(String title)
{
super (title);
JButton button1,button2,button3,button4;
JPanel panel1,panel2;
button1=new JButton("查询房屋信息");
button2=new JButton("租房");
button3=new JButton("退房");
button4=new JButton("退出");
panel1=new JPanel();
panel2=new JPanel();
panel2.add(button1);
panel2.add(button2);
panel2.add(button3);
panel2.add(button4);
panel2.setLayout(new FlowLayout());
panel1.setBackground(Color.CYAN);
Container cp=getContentPane();
cp.add(panel1,BorderLayout.CENTER);
cp.add(panel2,BorderLayout.SOUTH);
AL listener=new AL();
button4.addActionListener(listener);
setSize(800,600);
setVisible(true);
setDefaultCloseOperation(JFrame. EXIT_ON_CLOSE);
}
}
class AL implements ActionListener{
public void actionPerformed(ActionEvent e){
if((JButton)e.getSource()==button4)
JFrame.EXIT_ON_CLOSE; 
}
}
public class AFrame{
public static void main(String args[]){
new AFramee("123");
}
}

这代码我想实现按button4时 窗口关闭 但是按了没反应 求各位指教指教

private JButton getExitBtn() {
        if (exitBtn == null) {
            exitBtn = new JButton("退 出");
            exitBtn.setBounds(new Rectangle(331, 229, 104, 23));
            exitBtn.setName("退出按钮");
            exitBtn.addMouseListener(new java.awt.event.MouseAdapter() {
                public void mouseClicked(java.awt.event.MouseEvent e) {
                   
                    System.exit(0);
                }
            });
        }
        return exitBtn;
    }

JFrame.EXIT_ON_CLOSE更本不是退出语句，只是一个常量
怎么可能退出与关闭UI,帮你改了actionPerformed的方法
更多发现看我的博客
Java codepublic void actionPerformed(ActionEvent e){
if((JButton)e.getSource()==button4) {
 this.setVisible(true);
 this.dispose();
}