Java KeyEvent registers keys that aren't being pressed

Question

I want a program that will read what keys are pressed in one file using KeyEvent, and write it to console in the next. I have the keys Q & W set up, but whenever I try to run the program, it spams "Key Q Pressed" and "Key W Pressed"

I've tried changing KeyPressed to KeyTyped, nothing. Seperate functions for KeyPressed, KeyTyped, and KeyReleased, nothing. Removing CHAR_UNDEFINED, nothing.

Main IsKeyPressed.java

import java.awt.KeyEventDispatcher;
import java.awt.KeyboardFocusManager;
import java.awt.event.KeyEvent;

public class IsKeyPressed {
    private static volatile boolean qPressed = false;
    private static volatile boolean wPressed = false;

    public static boolean isQPressed() {
        synchronized (IsKeyPressed.class) {
            return qPressed;
        }
    }

    public static boolean isWPressed() {
        synchronized (IsKeyPressed.class) {
            return wPressed;
        }
    }

    public static void main(String[] args) {
        KeyboardFocusManager.getCurrentKeyboardFocusManager().addKeyEventDispatcher(new KeyEventDispatcher() {

            @Override
            public boolean dispatchKeyEvent(KeyEvent ke) {
                synchronized (IsKeyPressed.class) {
                    switch(ke.getID()) {
                    case KeyEvent.KEY_PRESSED:
                        if (ke.getKeyCode() == KeyEvent.VK_W) {
                            wPressed = true;
                        } else if (ke.getKeyCode() == KeyEvent.VK_Q) {
                            qPressed = true;
                        }
                        break;

                    case KeyEvent.KEY_RELEASED:
                        if (ke.getKeyCode() == KeyEvent.VK_W) {
                            wPressed = false;
                        } else if (ke.getKeyCode() == KeyEvent.VK_Q) {
                            qPressed = false;
                        }
                        break;
                    }
                    return false;
                }
            }
        });
    }

    public void keyTyped(KeyEvent ke) {
        //test
    }

    public void keyPressed(KeyEvent ke) {
        //test
    }

    public void keyReleased(KeyEvent ke) {
        //test
    }
}

Public class in Test.java

static boolean randomVariableName = true;

    public static void main(String[] args) {
        while (randomVariableName == true) {
            if (IsKeyPressed.isWPressed()); {
                System.out.println("keydown.W");
            }
            if (IsKeyPressed.isQPressed()); {
                System.out.println("keydown.Q");
            }
        }
    }

I expect hitting Q on my keyboard will make the console print keydown.Q, but instead it just spams keydown.Q and keydown.W

Possible duplicate of [Semicolon at end of 'if' statement](https://stackoverflow.com/questions/14112515/semicolon-at-end-of-if-statement) — Tom, Jun 05 '19 at 09:05

score 2 · Answer 1 · answered Jun 05 '19 at 00:23

following makes your code spam:

 if (IsKeyPressed.isWPressed()); {
     System.out.println("keydown.W");
 }

The semicolon after isWPressed() terminates the expression, so always true...

Without spam:

 if (IsKeyPressed.isWPressed()) {
     System.out.println("keydown.W");
 }

Also I think you will not have the possiblity to get the keys by a KeyboardFocusManager. At least you must start a Swing JFrame or a AWT window to get the events. Doing this you can also simply add keylisteners or key mapping to components (e.g. a JTextField )

Fetching events outside your own application is - IMHO - not possible with Java.

Java KeyEvent registers keys that aren't being pressed

1 Answers1