Java KeyPressed - Can't Detect If Spacebar is Being Pressed If Other Keys Are Too

Question

As the title suggests, in my Java game, I cannot detect if I'm pressing the spacebar and other keys at the same time.

For example, spacebar is the shoot key, and the arrow keys make the player move. If I am pressing the up arrow key and the left arrow key and the spacebar, then it should shoot a bullet up and to the left.

However, after using multiple System.out.println(); to debug, I've found that if I am pressing two keys, it is not detecting the spacebar if it's pressed.

public void keyPressed(KeyEvent e) {


if(e.getKeyCode() == 32){
    pressingSpacebar = true;
    System.out.println("Spacebar pressed true");
}


    // Up arrow key
    if(e.getKeyCode() == 38){
        up = true;
        System.out.println("Up = true");
    }
    // Down arrow key
    if(e.getKeyCode() == 40){
        down = true;
        System.out.println("Down = true");

    }
    // Right arrow key
    if(e.getKeyCode() == 39){
        right = true;
        System.out.println("Right = true");
    }
    // Left arrow key
    if(e.getKeyCode() == 37){
        left = true;
        System.out.println("Left = true");
    }
}

Then in keyReleased:

public void keyReleased(KeyEvent e) {
    if(e.getKeyCode() == 38){
        up = false;
        repaint();
    }
    if(e.getKeyCode() == 40){
        down = false;
        repaint();
    }
    if(e.getKeyCode() == 39){
        right = false;
        repaint();
    }
    if(e.getKeyCode() == 37){
        left = false;
        repaint();
    }
    if(e.getKeyCode() == 32){
        pressingSpacebar = false;
    }
}

This is how I am checking if you are pressing the spacebar and multiple keys:

if(pressingSpacebar){
        if(right == true && down == true && up == false && left == false){
            // Shoot bullet
        }
}   

Why isn't the spacebar being detected? If I don't check for spacebar being pressed the bullets shoot fine, but when I check for the spacebar it just doesn't detect it.

Note: I have read other posts similar to this question but the answers were not very helpful. I am a sorta newbie when it comes to this stuff so try to give a simple answer or explain it a bit. Thanks in advance!

Answer 1

A KeyEvent is only generated for the last key pressed, so you need to keep track of a key when it is pressed (for example by adding it to a HashMap) and then on a keyReleased you need to remove the key from the HashMap.

The better way to do this is to use Key Bindings (not a KeyListener) to bind the KeyStroke to an Action.

Check out the KeyboardAnimation example found in Motion Using the Keyboard. It explains more about Key Bindings and provides a full working example of handling the Up/Down/Right/Left keys. In general any two keys can be held down at one time to give diagonal motion.

The logic will also work with 3 keys, but as has already been mentioned the keyboard itself may not support that many keys pressed at one time.

Answer 2

I think you should try all conditions in a single construct itself.

Try it -

if(pressingSpacebar && right && down && !up && !left){
            // Shoot bullet
}

Answer 3

I've encountered a similar problem. I found out that there is no guarantee on that simultaneously pressing keys and holding them will trigger key pressed event more than once for each key. So if you're relying on that you need to keep that in mind.