KeyStroke release detected even if I don't release the key

Question

After reading some tutorials I decided to switch from KeyListeners to KeyBindings. I think I have understood how they work, but I can't figure out why this little program detects a key release even if I don't release the key. EDIT: I am on a Linux machine.

    //KeyBindingsTest.java
    import javax.swing.*;
import java.awt.event.*;

public class KeyBindingsTest{
    private JFrame w = new JFrame();
    private JComponent j = new JPanel();
    public KeyBindingsTest(){
        w.setSize(400,400);
        w.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        w.setVisible(true);
        setKeyBindings();
        w.add(j);
    }

    public static void main(String[] args){
        new KeyBindingsTest();
    }

    private void setKeyBindings(){
        InputMap im = j.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);
        ActionMap am = j.getActionMap();
        im.put(KeyStroke.getKeyStroke(KeyEvent.VK_1, 0, false), "pressed");
        im.put(KeyStroke.getKeyStroke(KeyEvent.VK_1, 0, true), "released");

        am.put("pressed", new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent e) {
                System.out.println("Pressed");
            }
        });

        am.put("released", new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent e) {
                System.out.println("Released");
            }
        });
        j.setFocusable(true);
        j.requestFocusInWindow();      
    }
}

If I hold down the "1" key I expect the program to print continuously:

Pressed 
Pressed 
Pressed...

but it prints:

Pressed
Released
Pressed
Released...

I must be missing something, something very simple.

EDIT: now I've come up with a dirty dirty workaround, but I still hope someone will explain how to solve this in the appropriate way. Here it is:

            // the beginning of the file should stay the same
    private void setKeyBindings(){
        InputMap im = getInputMap(JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT);
        ActionMap am = getActionMap();
        im.put(KeyStroke.getKeyStroke(KeyEvent.VK_1, 0, false), "pressed");
        im.put(KeyStroke.getKeyStroke(KeyEvent.VK_1, 0, true), "released");

        class MyAction extends AbstractAction{
            private String s;
            public MyAction(String s){
                this.s = s;
            }
            @Override
            public void actionPerformed(ActionEvent e) {
                if(s.equals("pressed"))setKeyPressed();
                else if(s.equals("released"))tryToSetKeyReleased();
            }
        }

        am.put("pressed", new MyAction("pressed"));
        am.put("released", new MyAction("released"));

        setFocusable(true);
        requestFocusInWindow();   


    }

    public boolean pressed = false;
    public void setKeyPressed(){System.out.println("key pressed");pressed =true;}
    public void setKeyReleased(){System.out.println("key released");pressed = false;}
    public void tryToSetKeyReleased(){
        pressed = false;
        (new Thread(
                new Runnable(){
                    @Override
                    public void run() {
                        try{Thread.sleep(5);}
                        catch(Exception e){;}
                        if(pressed==false)setKeyReleased();
                    }

                }
        )).start();
    }

this is correct output from KeyEvents, is based on setting from Native OS — mKorbel, Nov 06 '13 at 11:34
then how do I distinguish between key-held-down and key-released in my program? — Festa Der Bresaola, Nov 06 '13 at 12:55

score 2 · Answer 1 · answered Nov 06 '13 at 11:38

2

This has to do with the operating system. If you continuously press a character in a notepad for instance it will continuously print that character. So, it continuously sends press-release signals.

answered Nov 06 '13 at 11:38

nelly

417
3
9

Thanks. But then how can I detect key presses and releases separately? Because using KeyListener there was no ambiguity, the key-release event was fired only when the key was actually released. – Festa Der Bresaola Nov 06 '13 at 12:52
1

I now see that this is a linux-related bug. Windows give multiple key pressed, but only one key released event, at the end. Check this thread: http://stackoverflow.com/questions/1736828/how-to-stop-repeated-keypressed-keyreleased-events-in-swing – nelly Nov 06 '13 at 13:06
Damn, that bug is 15 years old! :( How is it possible? It's also weird because in that thread they have this issue with KeyListeners, while I have never had this problem when I was using them. The proposed workaround fixes the KeyListeners, but I will try to adapt it to KeyBindings. – Festa Der Bresaola Nov 06 '13 at 14:45

KeyStroke release detected even if I don't release the key

1 Answers1