This section provides a tutorial example on how to use java.awt.event.ActionListener, button action listener interface, to catch events fired by JMenuItem objects.
Like any other user interface components, JMenuItem objects also fire events when users interact with them.
If you want to perform a task when an event occurs on a JMenuItem object, you need to add an event listener to that JMenuItem item object.
Because a JMenuItem is a sub class of AbstractButton, it shares the listener interface and event class with AbstractButton:
java.awt.event.ActionListener - An AWT interface that allows you to implement your own button event handler methods:
actionPerformed(ActionEvent) - Event handler method called when the associated button is clicked. You need to implement this method to perform your own task.
java.awt.event.ActionEvent - An AWT class that represents an event occurred on an action button. The most important method in this class is:
getActionCommand() - Method returns the action command string.
Here is an example program I wrote to test the MenuListener interface:
/**
* MenuItemActionListenerTest.java
* Copyright (c) 2009 by Dr. Herong Yang, http://www.herongyang.com/
*/
import java.awt.event.*;
import javax.swing.*;
public class MenuItemActionListenerTest {
JFrame myFrame = null;
public static void main(String[] a) {
(new MenuItemActionListenerTest()).test();
}
private void test() {
myFrame = new JFrame("Menu Listener Test");
myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
myFrame.setBounds(50,50,250,150);
myFrame.setContentPane(new JDesktopPane());
JMenuBar myMenuBar = new JMenuBar();
JMenu myMenu = getFileMenu();
myMenuBar.add(myMenu);
myMenu = getColorMenu();
myMenuBar.add(myMenu);
myMenu = getOptionMenu();
myMenuBar.add(myMenu);
MyMenuItem myItem = new MyMenuItem("Help");
myMenuBar.add(myItem);
myFrame.setJMenuBar(myMenuBar);
myFrame.setVisible(true);
}
private JMenu getFileMenu() {
JMenu myMenu = new JMenu("File");
MyMenuItem myItem = new MyMenuItem("Open");
myMenu.add(myItem);
myItem = new MyMenuItem("Close");
myMenu.add(myItem);
myMenu.addSeparator();
myItem = new MyMenuItem("Exit");
myMenu.add(myItem);
return myMenu;
}
private JMenu getColorMenu() {
JMenu myMenu = new JMenu("Color");
JMenuItem myItem = new MyMenuItem("Red");
myMenu.add(myItem);
myItem = new MyMenuItem("Green");
myMenu.add(myItem);
myItem = new MyMenuItem("Blue");
myMenu.add(myItem);
return myMenu;
}
private JMenu getOptionMenu() {
JMenu myMenu = new JMenu("Option");
JMenuItem myItem = new MyMenuItem("Sound");
myMenu.add(myItem);
myItem = new MyMenuItem("Auto save");
myMenu.add(myItem);
return myMenu;
}
private class MyMenuItem extends JMenuItem
implements ActionListener {
public MyMenuItem(String text) {
super(text);
addActionListener(this);
}
public void actionPerformed(ActionEvent e) {
System.out.println("Item clicked: "+e.getActionCommand());
}
}
}
If you run this example, you will see the frame window shows up with the menu bar like this:
If you click the "Help" menu item, click "Open" and "Close" in the "File" menu,
then click "Red", "Green" and "Blue" in the "Color" menu,
you will see some messages printed on the Java console window:
Item clicked: Help
Item clicked: Open
Item clicked: Close
Item clicked: Red
Item clicked: Green
Item clicked: Blue
Interesting notes about this tutorial example:
"private class MyMenuItem extends JMenuItem implements ActionListener" declaration is used
to create an inner class, MyMenuItem, which extends JMenuItem, implements ActionListener, and adds itself to handle action events.
"addActionListener(this);" statement is used to add my inner class, MyMenuItem, itself to handle action events.
"e.getActionCommand()" expression is used to get action command string, the menu item button text in this case.
Sample programs listed in this section have been tested with JDK 1.6.0.
