Key binding won't work with alt-up and alt-left arrow combined

Question

I was playing with key binding trying to create a small app where a timer is started with the press of an alt-arrow key and stopped when the key is released. The timers append Strings to a JTextArea telling which alt-arrow key is currently pressed.
This program works, and in fact if you press a combination of any two keys, both timers will work simultaneously, that is unless you press both up arrow and left arrow together. Can anyone see a bug in the program that explains why it won't work for these two particular keys when combined? Thanks in advance, Pete
My SSCCE,
KeyBindingEg.java
package javaforum2009;
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.InputEvent;
import java.awt.event.KeyEvent;
import javax.swing.*;
public class KeyBindingEg {
  // parallel arrays -- sorry
  private static final int[] ARROW_KEYS = {
      KeyEvent.VK_UP, KeyEvent.VK_DOWN,
      KeyEvent.VK_LEFT, KeyEvent.VK_RIGHT };
  private static final String[] ACTION_STRINGS = {
    "Up", "Down",
    "Left", "Right" };
  private static final String PRESSED = "PRESSED";
  private static final String RELEASED = "RELEASED";
  private static final int TIMER_DELAY = 100;
  private JPanel mainPanel = new JPanel();
  private JTextArea textArea = new JTextArea(20, 30);
  public KeyBindingEg() {
    JPanel northPanel = new JPanel();
    northPanel.add(new JLabel("This JTextField has the focus: "));
    northPanel.add(new JTextField(10));
    textArea.setEditable(false);
    mainPanel.setLayout(new BorderLayout());
    mainPanel.add(northPanel, BorderLayout.NORTH);
    mainPanel.add(new JScrollPane(textArea), BorderLayout.CENTER);
    setBindings();
  private void setBindings() {
    int context = JComponent.WHEN_IN_FOCUSED_WINDOW;
    InputMap inputMap = mainPanel.getInputMap(context);
    ActionMap actionMap = mainPanel.getActionMap();
    for (int i = 0; i < ARROW_KEYS.length; i++) {
      // timer is started on key press and stopped
      // on key release.
      Timer timer = new Timer(TIMER_DELAY, new KeyTimerListener(
          ACTION_STRINGS));
timer.setInitialDelay(0);
// get input maps for all alt-arrow keys for both key press
// and key release
inputMap.put(KeyStroke.getKeyStroke(ARROW_KEYS[i],
InputEvent.ALT_DOWN_MASK, false), ACTION_STRINGS[i] + PRESSED);
inputMap.put(KeyStroke.getKeyStroke(ARROW_KEYS[i],
InputEvent.ALT_DOWN_MASK, true), ACTION_STRINGS[i] + RELEASED);
// set corresponding actions for the two different key presses above
actionMap.put(ACTION_STRINGS[i] + PRESSED, new ArrowKeyAction(false, timer));
actionMap.put(ACTION_STRINGS[i] + RELEASED, new ArrowKeyAction(true, timer));
@SuppressWarnings("serial")
private class ArrowKeyAction extends AbstractAction {
private boolean onKeyRelease;
private Timer swingTimer;
public ArrowKeyAction(boolean onKeyRelease, Timer swingTimer) {
this.onKeyRelease = onKeyRelease;
this.swingTimer = swingTimer;
public void actionPerformed(ActionEvent arg0) {
if (onKeyRelease) {
swingTimer.stop();
} else {
swingTimer.start();
private class KeyTimerListener implements ActionListener {
private String actionString;
public KeyTimerListener(String actionString) {
this.actionString = actionString;
public void actionPerformed(ActionEvent arg0) {
textArea.append(actionString + " pressed\n");
public JComponent getPanel() {
return mainPanel;
private static void createAndShowGUI() {
JFrame frame = new JFrame("KeyBindings Example");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new KeyBindingEg().getPanel());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();

Answer 1

camickr wrote:
I noticed the problem a while ago with a similiar example and asked the same question to which nobody could give an explanation. The same observations seem to apply to your example in that using the numpad arrow keys work without a problem.
[http://forums.sun.com/thread.jspa?threadID=5176816]
Yes indeed. I suppose (as always) I should have searched the forum first before asking the question. Thanks for the link and info.
/Pete