ActionListeners在JMenuBar中不起作用

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class MenuExample {
    public static void main(String[] args) {
        JFrame frame = new JFrame("Menu Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JMenuBar menuBar = new JMenuBar();
        frame.setJMenuBar(menuBar);

        JMenu menu = new JMenu("File");
        menuBar.add(menu);

        JMenuItem menuItem = new JMenuItem("Open");
        menuItem.setActionCommand("open");
        menuItem.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                String command = e.getActionCommand();
                if (command.equals("open")) {
                    // 处理打开文件的逻辑
                    System.out.println("Open menu item clicked");
                }
            }
        });
        menu.add(menuItem);

        frame.setSize(300, 200);
        frame.setVisible(true);
    }
}