Java: Menus

// File   : menus/MenuDemo.java
// Purpose: Simple demo of building menus.  main program.
// Author : Fred Swartz
// Date   : 2000-04-26 (Rota), 2002-05-01 (Sicilia), 2005-12-01 (Pfalz)

import javax.swing.*;

////////////////////////////////////////////////////////////// MenuDemo
public class MenuDemo {
    //============================================================ main
    public static void main(String[] args) {
        JFrame win = new MenuDemoGUI();
        win.setVisible(true);
    }
}

// File   : menus/MenuDemoGUI.java
// Purpose: GUI for menu demo.  Subclasses JFrame and defines a method
//          which generates menubar.
// Author : Fred Swartz
// Date   : 2000-04-26 (Rota), 2002-05-01 (Sicilia), 2005-12-01 (Pfalz)

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

/////////////////////////////////////////////////////////////// MenuDemoGUI
class MenuDemoGUI extends JFrame {
    private JTextArea m_editArea = new JTextArea(20, 50);

    //... Menuitems are buttons. They are instance variables
    //    so they can be en-/disabled by various actions.
    private JMenuItem m_openItem = new JMenuItem("Open"); // create new menu item
    private JMenuItem m_quitItem = new JMenuItem("Quit"); // another menu item
    private JMenuItem m_copyItem = new JMenuItem("Copy");
    private JMenuItem m_pasteItem= new JMenuItem("Paste");

    //========================================================== constructor
    public MenuDemoGUI() {
        //... Add listeners to menu items
        m_openItem.addActionListener(new OpenAction());
        m_quitItem.addActionListener(new QuitAction());

        //... Copy and Paste don't have listeners yet, so disable them.
        m_copyItem.setEnabled(false);
        m_pasteItem.setEnabled(false);

        //... Add the single component.
        JPanel content = new JPanel();
        content.setLayout(new BorderLayout());
        content.add(m_editArea, BorderLayout.CENTER);

        //... Set content pane and menu bar.
        this.setContentPane(content);
        this.setJMenuBar(createMenubar());

        //... Finish the window.
        this.setTitle("Menu Demo");
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.pack();
    }


    //==================================================== createMenubar
    // It's not uncommon to write a method that produces the menubar.
    // It gives a little better organization to the program
    // and doesn't mix content pane and menu construction, but
    // there is no real need to separate it.

    private JMenuBar createMenubar() {
        //... Menubar, menus, menu items.  Use indentation to show structure.
        JMenuBar menubar = new JMenuBar();  // declare and create new menu bar
            JMenu fileMenu = new JMenu("File");// declare and create new menu
                menubar.add(fileMenu);         // add the menu to the menubar
                fileMenu.add(m_openItem);   // add the menu item to the menu
                fileMenu.addSeparator();    // add separator line to menu
                fileMenu.add(m_quitItem);
            JMenu editMenu = new JMenu("Edit");
                menubar.add(editMenu);
                editMenu.add(m_copyItem);
                editMenu.add(m_pasteItem);
        return menubar;
    }


    ///////////////////////////////////////////////////////////// OpenAction
    class OpenAction implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            JOptionPane.showMessageDialog(MenuDemoGUI.this, "Sorry, can't open anything");
        }
    }

    ///////////////////////////////////////////////////////////// QuitAction
    class QuitAction implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            System.exit(0);  // terminate this program
        }
    }
}