Re: Keyboard state (instead of keyboard events)

Knute Johnson <>
Wed, 31 Dec 2008 11:07:04 -0800
Philipp Gressly wrote:

Philipp Gressly wrote:

Hello everybody

I am programming a "moon-lander" and want to check every 100 ms if a
certain key is pressed.
The keyboard events (key-pressed, key-released and key-typed) are
not helpful, because the operating System (linux im my case)
generates key-releases and key-presses at its own (depending on the
"key repeat speed").

Is there a command to satisfy the following interface easily?

public interface KeyState {
  boolean isKeyDown(char keyCode);

With all your help, I have implemented the code below.

It works in 99%, because the gnome "keyPressed.getWhen()" has mostly
the same value
as a previous "keyReleased.getWhen()" in case of the
Very rarely the below mentioned code reports "down: false", but it
should be "down: true".
It would be interesting to have some feedback about other operating


import javax.swing.JFrame;
import java.awt.event.*;

 * @author Philipp Gressly (
 * after a code from Luther :

public class IgnoreRepeats extends JFrame implements KeyListener,
Runnable {

    private long oldWhen = 0L;
    public boolean down;

    /* starter */
    public static void main(String[] _) {
        new IgnoreRepeats("Test Frame").top(); }

    public IgnoreRepeats(String name){
        super(name); }

    private void top() {
        super.addKeyListener (this) ;
        super.setDefaultCloseOperation (EXIT_ON_CLOSE);
        setSize (300, 300) ;
        setVisible (true) ;
        new Thread(this). start(); }

    public void run() {
        while (true) {
            System.out.println("down: " + down);
            try {
            } catch (InterruptedException e) { }

    public void keyReleased(final KeyEvent e) {
        if (oldWhen == e.getWhen()) return;
        down = false; }

    public void keyPressed(final KeyEvent e) {
        long now = e.getWhen();
        if (oldWhen == now) return;
        oldWhen = now;
        down = true; }

    /* ignore */
    public void keyTyped(KeyEvent e) {}

} // end "IgnoreRepeats"

Throw out the getWhen() part, you don't need it. Just set the flag when
the key is pressed, and clear it when it's released.


Knute Johnson
email s/nospam/knute2008/

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