Thread supposed to block keyevents

[Dajka Ferenc]

Hi There!

I wrote 2 class, the first is a canvas wich can listen to keyevents, the second is a thread wich sets a boolean variable to true, than 2 secs later to false. While the variable is true, one shouldnt supposed to change anything with a keypress, but one can. How can this be possible? Thanks.

The listeners code.

 @Override
    public void keyPressed(KeyEvent e) {
        if(!keyPressed){
            KeyboardBlocker kBB = new KeyboardBlocker(keyPressed);
            kBB.start();
            switch(e.getKeyCode()){
                case KeyEvent.VK_UP:
                    rotUpperClockwise(upperRow, CLOCKWISE, 'Z');
                    break;
                case KeyEvent.VK_DOWN:
                    rotUpperClockwise(upperRow, COUNTERCLOCKWISE, 'Z');    
                    break;
                case KeyEvent.VK_LEFT:
                    break;
                case KeyEvent.VK_RIGHT:
                    break;
            }
        }
    }

the threads code:

package szakdoga_real;

import java.util.logging.Level;
import java.util.logging.Logger;

public class KeyboardBlocker extends Thread{

    private Boolean isKeyPressed;

    public KeyboardBlocker(Boolean isKeyPressed) {
        this.isKeyPressed = isKeyPressed;
    }
    
    @Override
    public void run() {
        isKeyPressed = true;
        System.out.println(isKeyPressed);
        try {
            Thread.sleep(2000);
        } catch (InterruptedException ex) {
            Logger.getLogger(KeyboardBlocker.class.getName()).log(Level.SEVERE, null, ex);
        }
        isKeyPressed = false;
        System.out.println(isKeyPressed);
    }
    
}

[Alexander Kober]

There are at least two things wrong with the implementation:

1) It seems you start a thread and immediately expect it to be running. This is not the case. Thread#start schedules a thread for execution, but that may happen at any time. Usually, thread startup will happen very fast, but not immediately.
2) Though this is may be unintuitive, never use a plain boolean for synchronization between threads, at the very least make it volatile or use an AtomicBoolean.

That being said, if I understand your code correctly, you simply want to block key input for 2 seconds, correct? Why create a thread in the first place then? When your keyPressed method is executed, take the current system time (System.currentTimeMillis()) and assign it to a variable. Simply add a check at the beginning of the method to see when the last keyPress was processed:

if (System.currentTimeMillis() - lastKeyPress < 2000)
  return;
lastKeyPress = System.currentTimeMillis();
...

[Dajka Ferenc]

It was cool. Thanks for it!

[Darryl Burke]

Dajka, please BeForthrightWhenCrossPostingToOtherSites
http://www.java-forums.org/threads-synchronization/56540-thread-supposed-block-keyevents.html

edit And http://www.programmingforums.org/thread40728.html

Any more?

[Dajka Ferenc]

ok than.