Remove an Actor in Greenfoot if he´s on the top

Question

I´m building my own Space Invaders in Java with Greenfoot and I have a Spaceship which shoots the Aliens, but the Bullets stop at the top of the map and stay there so I wrote this method which should remove a bullet if it hits the top of the but it doesn't work. What´s the problem?

public void disappearIfOnTop() {
    Actor Bullet = getOneIntersectingObject(Actor.class);
    getY();

    if(getY() == 0) {
        World world;
        world = getWorld();
        world.removeObject(Bullet);
    }
}

Edit: they are getting removed if they hit another bullet which is stuck on the top.

Answer 1

The method getOneIntersectingObject() returns a null if there is no other actor.

You might want to check this to be sure:

public void disappearIfOnTop() {
    if (getY() == 0) {
        Actor bullet = getOneIntersectingObject(Actor.class);
        if (bullet == null) {
            setLocation(getX(), 50); // move down if no other is around
        } else {
            setLocation(getX(), 100); // move further down if another is around
        }
    }
}

If the method getOneIntersectingObject() returns a reference to an actor, your current method is removing that one, not the one who is at Y=0. (BTW, don't use variable names starting with uppercase letters. By convention, this is reserved for classes.)

You can simplify your method to:

public void disappearIfOnTop() {
    if (getY() == 0) {
        getWorld().removeObject(this);
    }
}