多级菜单（java GUI）

话不多说，先来效果：

源码如下：

package javaBasic;

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

public class Menu {
	public static void main(String[] args) {
		MyFrame3 frame = new MyFrame3();
	}
}

class MyFrame3 extends JFrame{
	JMenuBar mb;//菜单栏
	JMenu m1,m2,m3,m4;//菜单
	JMenuItem mi1,mi2,mi3,mi11,mi12;//菜单项

	MyFrame3()
	{
		this.setTitle("eclipse-worksplace");
		this.setSize(500,400);
		this.setLocationRelativeTo(null);
		this.setLayout(new FlowLayout());

		mb = new JMenuBar();
		m1 = new JMenu("File");
		m2 = new JMenu("Edit");
		m3 = new JMenu("Source");
		m4 = new JMenu("new");
		mi1 = new JMenuItem("open file");
		mi2 = new JMenuItem("exit");
		mi11 = new JMenuItem("Java Project");
		mi12 = new JMenuItem("Project");

		mb.add(m1);
		mb.add(m2);
		mb.add(m3);
		m1.add(m4);
		m1.add(mi1);
		m1.add(mi2);
		m4.add(mi11);
		m4.add(mi12);
		this.setJMenuBar(mb);//注意设置菜单项的方法是set 不是add
		this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		this.setVisible(true);

		mi2.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				System.exit(0);
			}
		});
	}
}