This section provides a tutorial example on how to use setAccelerator() method to associate accelerators to menu items. Accelerators allows user to interact with menu items using keys on keyboard.
Keyboard mnemonics allows users to invoke a menu item with a single key. But the menu contains that menu item
be popped up first.
To users to invoke a menu item without its menu popped up, we need to assign an accelerator, key combination,
to that menu item with the setAccelerator() method. Here is how it works:
1. Assign difference accelerators, representing different key combinations, to different menu items.
2. Adding an action listener to each menu item.
3. When an accelerator, key combination, is pressed at any time, the menu item with the matching accelerator
will fire an action event.
Here is an example program I wrote to test the setAccelerator() method:
/**
* JMenuItemSetAcceleratorTest.java
* Copyright (c) 2009 by Dr. Herong Yang, http://www.herongyang.com/
*/
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
public class JMenuItemSetAcceleratorTest implements ActionListener {
JFrame myFrame = null;
public static void main(String[] a) {
(new JMenuItemSetAcceleratorTest()).test();
}
private void test() {
myFrame = new JFrame("Menu Item Accelerator 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);
JMenuItem myItem = new JMenuItem("Help");
myItem.setMnemonic(KeyEvent.VK_H);
myItem.setAccelerator(
KeyStroke.getKeyStroke(KeyEvent.VK_P, ActionEvent.CTRL_MASK));
myItem.addActionListener(this);
myMenuBar.add(myItem);
myFrame.setJMenuBar(myMenuBar);
myFrame.setVisible(true);
}
private JMenu getFileMenu() {
JMenu myMenu = new JMenu("File");
JMenuItem myItem = new JMenuItem("Open");
myMenu.add(myItem);
myItem = new JMenuItem("Close");
myMenu.add(myItem);
myMenu.addSeparator();
myItem = new JMenuItem("Exit");
myMenu.add(myItem);
return myMenu;
}
private JMenu getColorMenu() {
JMenu myMenu = new JMenu("Color");
ButtonGroup myGroup = new ButtonGroup();
JRadioButtonMenuItem myItem = new JRadioButtonMenuItem("Red");
myItem.setSelected(true);
myItem.setMnemonic(KeyEvent.VK_R);
myItem.setAccelerator(
KeyStroke.getKeyStroke(KeyEvent.VK_D, ActionEvent.CTRL_MASK));
myItem.addActionListener(this);
myGroup.add(myItem);
myMenu.add(myItem);
myItem = new JRadioButtonMenuItem("Green");
myItem.setMnemonic(KeyEvent.VK_G);
myItem.setAccelerator(
KeyStroke.getKeyStroke(KeyEvent.VK_N, ActionEvent.CTRL_MASK));
myItem.addActionListener(this);
myGroup.add(myItem);
myMenu.add(myItem);
myItem = new JRadioButtonMenuItem("Blue");
myItem.setMnemonic(KeyEvent.VK_B);
myItem.setAccelerator(
KeyStroke.getKeyStroke(KeyEvent.VK_E, ActionEvent.CTRL_MASK));
myItem.addActionListener(this);
myGroup.add(myItem);
myMenu.add(myItem);
return myMenu;
}
private JMenu getOptionMenu() {
JMenu myMenu = new JMenu("Option");
JMenuItem myItem = new JMenuItem("Sound");
myMenu.add(myItem);
myItem = new JMenuItem("Auto save");
myMenu.add(myItem);
return myMenu;
}
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:
Don't open the "Color" menu, and press <Ctrl>-d, <Ctrl>-n and <Ctrl>-e. Then repeat the test with the "Color" menu open.
Also try <Ctrl>-p.
You will see some messages printed on the Java console window:
Item clicked: Red
Item clicked: Green
Item clicked: Blue
Item clicked: Red
Item clicked: Green
Item clicked: Blue
Item clicked: Help
Interesting notes about this tutorial example:
I implemented only one interface on the main class: ActionListener.
"myItem.setAccelerator( KeyStroke.getKeyStroke( KeyEvent.VK_*, ActionEvent.CTRL_MASK ) );"
statement is used to assign a specific accelerator to a menu item.
Most GUI applications follow the convention of using <Ctrl> as the modifier key menu item accelerators.
When accelerator <Ctrl>-d was pressed, 1 action event was fired from the "Red" menu item,
because it has the matching accelerated assigned.
The accelerator on the "Help" menu item listed in the menu bar also works correctly.
Sample programs listed in this section have been tested with JDK 1.6.0.
