java - Preventing diagonal movement

I was originally fine with diagonal movement but it's clashing with my sprite animation...

    public void keyPressed(KeyEvent e){
    int key = e.getKeyCode();

    switch(key){
        case KeyEvent.VK_W:{
            dir = 3;
            velY = -speed;
            break;
        }

        case KeyEvent.VK_S:{
            dir = 2;
            velY = speed;
            break;
        }
        case KeyEvent.VK_A:{
            dir = 1;
            velX = -speed;
            break;
        }

        case KeyEvent.VK_D:{
            dir  = 0;
            velX = speed;
            break;
        }
    }
}

public void keyReleased(KeyEvent e){
    int key = e.getKeyCode();


    switch(key){
        case KeyEvent.VK_W:{
            velY = 0;
            break;
        }
        case KeyEvent.VK_S:{
            velY = 0;
            break;
        }

        case KeyEvent.VK_A:{
            velX = 0;
            break;
        }
        case KeyEvent.VK_D:{
            velX = 0;
            break;
        }
    }
}


    public void update(){
    y += velY;
    x += velX;
}

I thought that perhaps a switch statement or an if else statement would prevent multiple keys from firing at once, but it's not working out. I even tried synchronizing some methods but still to no avail. Any suggestions? And please ignore the dir variable I use it to find the direction the player is facing.

Answer

Obtaining multiple key presses can be found in this answer: How do I handle multiple key presses in Java?

Assign each one to a boolean variable and then check each key and add to the movement vector. Opposite keys will cancel out, and you can also test whether a key is already in use based on that.

if(noDiagonal)
{
    velX = 0;
    velY = 0;

    if(keyLeft) velX += -1;
    if(keyRight) velX += 1;

    if(velX == 0)
    {

        if(keyUp) velY += -1;
        if(keyDown) velY += 1;
    }
}
else // In case you change your mind...
{
    velX = 0;
    velY = 0;

    if(keyLeft) velX += -1;

    if(keyRight) velX += 1;
    if(keyUp) velY += -1;
    if(keyDown) velY += 1;

    // Normalize to prevent high speed diagonals
    float length = sqrt((velX * velX ) + (velY * velY ));
    velX = velX/length;
    velY = velY/length;
}
velX *= speed;

velY *= speed;

Pick which animation/direction to use based on the speed in that direction, rather than the key. This will make it easier to handle automatic animation later (like in a cutscene), or you can turn that part off individually (like if they're standing on a conveyer belt).