Java Swing窗体关闭事件的调用关系

import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
 
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
 
public class CloseEventDemo extends JFrame
{
 public static void main(String[] args)
 {
 new CloseEventDemo();
 }
 
 public CloseEventDemo()
 {
 // 创建一个面板
 JPanel paContent = new JPanel(new FlowLayout(FlowLayout.CENTER));
 paContent.setPreferredSize(new Dimension(400, 100));
 // 在面板中创建一个按钮用于关闭窗体
 JButton btn = new JButton("关闭");
 btn.setPreferredSize(new Dimension(100, 25));
 btn.addActionListener(new ActionListener()
 {
 
 public void actionPerformed(ActionEvent e)
 {
 closeFrame();
 }
 
 });
 // 向面板中加载按钮
 paContent.add(btn);
 
 // 设置面板
 this.setTitle("Close Event Demo");
 this.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
 this.setContentPane(paContent);
 this.pack();
 this.setLocationRelativeTo(null);
 this.setVisible(true);
 this.addWindowListener(new WindowAdapter()
 {
 public void windowClosing(WindowEvent e)
 {
 System.out.println("触发windowClosing事件");
 closeFrame();
 }
 
 public void windowClosed(WindowEvent e)
 {
 System.out.println("触发windowClosed事件");
 }
 });
 }
 
 // 关闭窗体
 private void closeFrame()
 {
 System.out.println("调用窗体关闭功能");
 int result = JOptionPane.showConfirmDialog(null, "是否要退出？", "退出确认", JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE);
 if (result == JOptionPane.YES_OPTION)
 this.dispose();
 }
}