[Java Swing] JMenu trong Java

Định viết bài về JMenu tuy nhiên khi tìm được bài code này thì nó rất đầy đủ, giải thích cũng tương đối rõ ràng.

Trước tiên chúng ta cần add một MenuBar vào JFrame, sau đó các JMenu được add vào MenuBar, các JMenuItem được add vào các JMenu.

Chương trình có cả JPopupmenu (khi click chuột phải).

Ngoài ra các bạn cần có ảnh làm icon trong menu, copy file ảnh vào trong package như thế này:

package nguyenvanquan7826.JMenu;

import java.awt.BorderLayout;
import java.awt.Container;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.awt.event.KeyEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

import javax.swing.ButtonGroup;
import javax.swing.ImageIcon;
import javax.swing.JCheckBoxMenuItem;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JPanel;
import javax.swing.JPopupMenu;
import javax.swing.JRadioButtonMenuItem;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.KeyStroke;

/* DemoRightClickMenu.java requires images/middle.gif. */

/*
 * Like MenuDemo, but with popup menus added.
 */
public class DemoJMenu implements ActionListener, ItemListener {
	JTextArea output;
	JScrollPane scrollPane;
	String newline = "
";

	public JMenuBar createMenuBar() {
		JMenuBar menuBar;
		JMenu menu, submenu;
		JMenuItem menuItem;
		JRadioButtonMenuItem rbMenuItem;
		JCheckBoxMenuItem cbMenuItem;

		// Create the menu bar.
		menuBar = new JMenuBar();

		// Build the first menu.
		menu = new JMenu("A Menu");
		menu.setMnemonic(KeyEvent.VK_A);
		menu.getAccessibleContext().setAccessibleDescription(
				"The only menu in this program that has menu items");
		menuBar.add(menu);

		// a group of JMenuItems
		menuItem = new JMenuItem("A text-only menu item", KeyEvent.VK_T);
		// menuItem.setMnemonic(KeyEvent.VK_T); //used constructor instead
		menuItem.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_1,
				ActionEvent.ALT_MASK));
		menuItem.getAccessibleContext().setAccessibleDescription(
				"This doesn't really do anything");
		menuItem.addActionListener(this);
		menu.add(menuItem);

		ImageIcon icon = createImageIcon("images/middle.gif");
		menuItem = new JMenuItem("Both text and icon", icon);
		menuItem.setMnemonic(KeyEvent.VK_B);
		menuItem.addActionListener(this);
		menu.add(menuItem);

		menuItem = new JMenuItem(icon);
		menuItem.setMnemonic(KeyEvent.VK_D);
		menuItem.addActionListener(this);
		menu.add(menuItem);

		// a group of radio button menu items
		menu.addSeparator();
		ButtonGroup group = new ButtonGroup();

		rbMenuItem = new JRadioButtonMenuItem("A radio button menu item");
		rbMenuItem.setSelected(true);
		rbMenuItem.setMnemonic(KeyEvent.VK_R);
		group.add(rbMenuItem);
		rbMenuItem.addActionListener(this);
		menu.add(rbMenuItem);

		rbMenuItem = new JRadioButtonMenuItem("Another one");
		rbMenuItem.setMnemonic(KeyEvent.VK_O);
		group.add(rbMenuItem);
		rbMenuItem.addActionListener(this);
		menu.add(rbMenuItem);

		// a group of check box menu items
		menu.addSeparator();
		cbMenuItem = new JCheckBoxMenuItem("A check box menu item");
		cbMenuItem.setMnemonic(KeyEvent.VK_C);
		cbMenuItem.addItemListener(this);
		menu.add(cbMenuItem);

		cbMenuItem = new JCheckBoxMenuItem("Another one");
		cbMenuItem.setMnemonic(KeyEvent.VK_H);
		cbMenuItem.addItemListener(this);
		menu.add(cbMenuItem);

		// a submenu
		menu.addSeparator();
		submenu = new JMenu("A submenu");
		submenu.setMnemonic(KeyEvent.VK_S);

		menuItem = new JMenuItem("An item in the submenu");
		menuItem.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_2,
				ActionEvent.ALT_MASK));
		menuItem.addActionListener(this);
		submenu.add(menuItem);

		menuItem = new JMenuItem("Another item");
		menuItem.addActionListener(this);
		submenu.add(menuItem);
		menu.add(submenu);

		// Build second menu in the menu bar.
		menu = new JMenu("Another Menu");
		menu.setMnemonic(KeyEvent.VK_N);
		menu.getAccessibleContext().setAccessibleDescription(
				"This menu does nothing");
		menuBar.add(menu);

		return menuBar;
	}

	public Container createContentPane() {
		// Create the content-pane-to-be.
		JPanel contentPane = new JPanel(new BorderLayout());
		contentPane.setOpaque(true);

		// Create a scrolled text area.
		output = new JTextArea(5, 30);
		output.setEditable(false);
		scrollPane = new JScrollPane(output);

		// Add the text area to the content pane.
		contentPane.add(scrollPane, BorderLayout.CENTER);

		return contentPane;
	}

	public void createPopupMenu() {
		JMenuItem menuItem;

		// Create the popup menu.
		JPopupMenu popup = new JPopupMenu();
		menuItem = new JMenuItem("A popup menu item");
		menuItem.addActionListener(this);
		popup.add(menuItem);
		menuItem = new JMenuItem("Another popup menu item");
		menuItem.addActionListener(this);
		popup.add(menuItem);

		// Add listener to the text area so the popup menu can come up.
		MouseListener popupListener = new PopupListener(popup);
		output.addMouseListener(popupListener);
	}

	public void actionPerformed(ActionEvent e) {
		JMenuItem source = (JMenuItem) (e.getSource());
		String s = "Action event detected." + newline + "    Event source: "
				+ source.getText() + " (an instance of " + getClassName(source)
				+ ")";
		output.append(s + newline);
		output.setCaretPosition(output.getDocument().getLength());
	}

	public void itemStateChanged(ItemEvent e) {
		JMenuItem source = (JMenuItem) (e.getSource());
		String s = "Item event detected."
				+ newline
				+ "    Event source: "
				+ source.getText()
				+ " (an instance of "
				+ getClassName(source)
				+ ")"
				+ newline
				+ "    New state: "
				+ ((e.getStateChange() == ItemEvent.SELECTED) ? "selected"
						: "unselected");
		output.append(s + newline);
		output.setCaretPosition(output.getDocument().getLength());
	}

	// Returns just the class name -- no package info.
	protected String getClassName(Object o) {
		String classString = o.getClass().getName();
		int dotIndex = classString.lastIndexOf(".");
		return classString.substring(dotIndex + 1);
	}

	/** Returns an ImageIcon, or null if the path was invalid. */
	protected static ImageIcon createImageIcon(String path) {
		java.net.URL imgURL = DemoJMenu.class.getResource(path);
		if (imgURL != null) {
			return new ImageIcon(imgURL);
		} else {
			System.err.println("Couldn't find file: " + path);
			return null;
		}
	}

	/**
	 * Create the GUI and show it. For thread safety, this method should be
	 * invoked from the event-dispatching thread.
	 */
	private static void createAndShowGUI() {
		// Create and set up the window.
		JFrame frame = new JFrame("DemoRightClickMenu");
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

		// Create/set menu bar and content pane.
		DemoJMenu demo = new DemoJMenu();
		frame.setJMenuBar(demo.createMenuBar());
		frame.setContentPane(demo.createContentPane());

		// Create and set up the popup menu.
		demo.createPopupMenu();

		// Display the window.
		frame.setSize(450, 260);
		frame.setVisible(true);
	}

	public static void main(String[] args) {
		// Schedule a job for the event-dispatching thread:
		// creating and showing this application's GUI.
		javax.swing.SwingUtilities.invokeLater(new Runnable() {
			public void run() {
				createAndShowGUI();
			}
		});
	}

	class PopupListener extends MouseAdapter {
		JPopupMenu popup;

		PopupListener(JPopupMenu popupMenu) {
			popup = popupMenu;
		}

		public void mousePressed(MouseEvent e) {
			maybeShowPopup(e);
		}

		public void mouseReleased(MouseEvent e) {
			maybeShowPopup(e);
		}

		private void maybeShowPopup(MouseEvent e) {
			if (e.isPopupTrigger()) {
				popup.show(e.getComponent(), e.getX(), e.getY());
			}
		}
	}
}

Đọc thêm: use menu, class jmenu, java swing