How to implement an anonymous class for event listening and processing in Java GUI

package com.sinosuperman.driver;import java.awt.Dimension;import java.awt.FlowLayout;import java.awt.Toolkit;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import javax.swing.JButton;import javax.swing.JFrame;import javax.swing.JOptionPane;import javax.swing.JPanel;public class MainBench {public static void main(String[] args) {JFrame frame = new MyFrame();}}class MyFrame extends JFrame {private static final long serialVersionUID = 1L;Toolkit tk = Toolkit.getDefaultToolkit();Dimension d = tk.getScreenSize();JPanel panel;public MyFrame() {panel = new MyPanel();this.add(panel);this.setSize((int) d.getWidth() / 2, (int) d.getHeight() / 2);this.setLocation((int) (d.getWidth() - this.getWidth()) / 2, (int) (d.getHeight() - this.getHeight()) / 2);this.setResizable(false);this.setVisible(true);}}class MyPanel extends JPanel {private static final long serialVersionUID = 5263963243638550398L;JButton okBtn;JButton exitBtn;public MyPanel() {this.setLayout(new FlowLayout(FlowLayout.CENTER));okBtn = new JButton("OK");exitBtn = new JButton("Exit");okBtn.addActionListener(new ActionListener() {public void actionPerformed(ActionEvent e) {JOptionPane.showConfirmDialog(null, "Are you sure?");}});exitBtn.addActionListener(new ActionListener() {public void actionPerformed(ActionEvent e) {int result = JOptionPane.showConfirmDialog(null, "Are you sure to exit?");if (result == JOptionPane.YES_OPTION) {System.exit(0);}}});this.add(okBtn);this.add(exitBtn);}}