Java KeyListener is giving me "Unknown keyCode:0x0"

Question

class KeyDemoFrame extends JFrame implements KeyListener
{
    String line1;
    KeyDemoFrame()
    {

        setTitle("hello");
        setSize(200,200);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
        addKeyListener(this);
    }

    public void keyTyped(KeyEvent e) {
        line1 = e.getKeyText(e.getKeyCode());
        JOptionPane.showMessageDialog(null, e.getKeyCode());
        JOptionPane.showMessageDialog(null, e.getKeyText(e.getKeyCode()));

    }

    public void keyPressed(KeyEvent e) {
    }

    public void keyReleased(KeyEvent e) {
    }
}

When I press any key, I get "0" for the first message dialog and "Unknown keyCode:0x0" for the second one.

What am I doing wrong?

Answer 1

You also need this to ctach the event, I think:

/**
     * Notification that an event has occured in the AWT event
     * system
     * 
     * @param e Details of the Event
     */
    public void eventDispatched(AWTEvent e) {
        if (e.getID() == KeyEvent.KEY_PRESSED) {
            keyPressed((KeyEvent) e);
        }
        if (e.getID() == KeyEvent.KEY_RELEASED) {
            keyReleased((KeyEvent) e);
        }
        if (e.getID() == KeyEvent.KEY_TYPED) {
            keyTyped((KeyEvent) e);
        }
    }

And by the way, you should work on your accept rate, otherwise it will be likley, that nobody will answer your questions.

Answer 2

From the Java Documentation for a KeyEvent:

getKeyCode
Returns: the integer code for an actual key on the keyboard. (For KEY_TYPED events, the keyCode is VK_UNDEFINED.)

You are using a keyTyped event, thus the value being returned is VK_UNDEFIED.

You can, however, just use the following to get the character that was typed:

JOptionPane.showMessageDialog(null, e.getKeyChar());

Answer 3

Use e.getKeyChar()

Answer 4

You may get three types of events: KEY_PRESSED, KEY_RELEASED, and KEY_TYPED events. The first two are associated to the action of pressing and releasing keys on the keyboard (which may or may not result in a character being typed), while the third one is associated with character input:

• For KEY_PRESSED and KEY_RELEASED events:
  • e.getKeyCode() returns a valid key code
  • e.getKeyChar() returns CHAR_UNDEFINED
• For KEY_TYPED events:
  • e.getKeyChar() returns a valid Unicode char
  • e.getKeyCode() returns VK_UNDEFINED

Your code is listening to KEY_TYPED events, but then using e.getKeyCode() which is only valid for KEY_PRESSED and KEY_RELEASED events.