Question

I found a very good tutorial about how to create games with Java2D. In this tutorial there is a section called ‘Moving sprites’ that shows how to move a little spacecraft image on the screen. I was playing with the craft and realized that it was “blocking” on screen sometimes. After some tests and thinking about the problem I found out that the blocking problem was happening because when you use the arrows of the keyboard sometimes you press Left and Right at same time for example, and this blocks the movement.

So my question is: how do I handle this kind of keyboard event – when you are pressing LEFT button keep pressing it and then press RIGHT button – so the character movement is not blocked?

I think this is very common to happen because when you are playing you switch from left to right but for an instant you are pressing left and right at the same time.

Answer 1

You can do this in multiple ways. One way is to use booleans in your program.

You can set booleans to true when you press a certain key and to false when you release them. ie:

int x,xSpeed;

boolean movingLeft  = false;
boolean movingRight = false;

public void keyPressed(KeyEvent e) {
    int key = e.getKeyCode();
    if(key == KeyEvent.VK_LEFT){
        movingLeft = true;
    }
    if(key == KeyEvent.VK_RIGHT){
        movingRight = true;
    } 
}

public void keyReleased(KeyEvent e) {
    int key = e.getKeyCode();
    if(key == KeyEvent.VK_LEFT){
        movingLeft = false;
    }
    if(key == KeyEvent.VK_RIGHT){
        movingRight = false;
    } 
}

public void moving(){
    if(movingLeft){
        x -= xSpeed;
    }
    if(movingRight){
        x += xSpeed;
    }
}

Ok let’s look at this code. Because we’re using the ‘else if’ you either move right, or you move left. I haven’t test this code so not quite sure if this will work 🙂

Let me know what you think and good luck!