Java KeyListener keyPressed method fires too fast

Question

If you use the java KeyListener class you know that if you hold down a key keyPressed will fire one KeyEvent, and then about half a second later will fire the same key many times very very fast. I would like to know if there is a way to keep the KeyEvents from firing too fast. I would like them to be at a nice constant rate of about once every 500 ms.

score 6 · Answer 1 · answered Mar 04 '11 at 21:45

6

You can, but the trick is to not slow down the firing of events, but to slow down how fast you process them:

KeyListener kl = new KeyListener() {
    private long lastPressProcessed = 0;

    @Override
    public void keyPressed(KeyEvent e) {
        if(System.currentTimeMillis() - lastPressProcessed > 500) {
            //Do your work here...
            lastPressProcessed = System.currentTimeMillis();
        }           
    }

    @Override
    public void keyTyped(KeyEvent e) {}

    @Override
    public void keyReleased(KeyEvent e) {   }

};

answered Mar 04 '11 at 21:45

This will only work well if the system key-repeat is very rapid. If it is, say, 400 ms between presses, then this may cause delays on up to 900 ms. – aioobe Mar 04 '11 at 21:48
@aioobe - There's no way around that, I think, other than changing the system autorepeat rate. It's a property of undersampling; there's going to be aliasing, which will appear as a jittery repeat time. If you are processing long streams of autorepeat events, then one can apply antialiasing techniques to reduce the jitter, but I doubt that long streams of autorepeat events are a common application. – Ted Hopp Mar 06 '11 at 00:19

aioobe · Answer 2 · 2011-03-04T21:55:42.930

No, this is completely system dependent. You would have to listen for keyPressed events, start a timer on your own that fires events at a fixed rate and stop it at the next keyReleased event.

Try something like this:

component.addKeyListener(new KeyListener() {

    Timer t = new Timer();
    TimerTask tt;

    @Override
    public void keyTyped(KeyEvent e) {
    }

    @Override
    public void keyReleased(KeyEvent e) {
        tt.cancel();
        tt = null;
    }

    @Override
    public void keyPressed(KeyEvent e) {
        if (tt != null)
            return;

        tt = new TimerTask() {
            @Override
            public void run() {
                System.out.println(System.currentTimeMillis() % 1000);
            }
        };

        t.scheduleAtFixedRate(tt, 0, 500);
    }
});

score 2 · Answer 3 · answered Mar 04 '11 at 21:46

2

This is controlled by your OS. But you could easily have your handler check how long it is since the last time it fired and respond accordingly.

answered Mar 04 '11 at 21:46

Matthew Gilliard

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score 1 · Answer 4 · answered Mar 04 '11 at 21:44

Usually the auto-repeat rate for keys is set by the system; I don't know if it's changeable from within Java. However, you can use the event arrival time to not react to one until 500ms after the last time you reacted (or after a key release, which should clear the timer for users who type fast).

Java KeyListener keyPressed method fires too fast

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