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

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

        setTitle("hello");
        setSize(200,200);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true开发者_StackOverflow中文版);
        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?

Looks like you have non-US layout as a default one. Java doesn't like it and generates events with invalid keycodes. As a countermeasure you can assign US a primary layout.

Use e.getKeyChar()

You need to get KeyCode in KeyPressed event and then you can use it in KeyTyped, of course the variable you will use have to be declared outside these two events.

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());

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.

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);
        }
    }