Question

I am working on a school assignment in java and i have come across an error i can’t find an answer on.
Somehow, when i call the gethit() method on an object returned by iterator.next() i get a stack overflow exception.
I suspect because the gethit() method (in this specific case) calls on itself recursively. Even though, i think it is strange to get a stack overflow since the recursion only goes 2 or 3 levels deep and my objects don’t use an excessive amount of memory.

The shoot() method that makes the first call of gethit()

public void shoot() {
    assert canHaveAsEnergy(energy - 1000);

    //Search the target position.
    Position laserPos = new Position(getPos().getX(), getPos().getY(), getPos().getBoard());
    do {
        long nextX = laserPos.getX() + new Double(orientation.getDirection().getX()).longValue();
        long nextY = laserPos.getY() + new Double(orientation.getDirection().getY()).longValue();
        laserPos.setX(nextX);
        laserPos.setY(nextY);
    } while (getPos().getBoard().canHaveAsPosition(laserPos) && (! getPos().getBoard().hasAsPosition(laserPos)));
    //Hit every entity on the target position. 
    for (Entity entity : getPos().getBoard().getAllEntitiesOn(laserPos)) {
        entity.getHit();
    }
    setEnergy(energy - 1000);
}

The getHit() method that recursively calls on itself.

public void getHit() {
    ArrayList<Position> neighbours = new ArrayList<Position>();
    Position northPos = new Position(getPos().getX(), getPos().getY() - 1, getPos().getBoard());
    Position eastPos = new Position(getPos().getX() + 1, getPos().getY(), getPos().getBoard());
    Position southPos = new Position(getPos().getX(), getPos().getY() + 1, getPos().getBoard());
    Position westPos = new Position(getPos().getX() - 1, getPos().getY(), getPos().getBoard());
    neighbours.add(northPos);
    neighbours.add(eastPos);
    neighbours.add(southPos);
    neighbours.add(westPos);

    for (Position pos : neighbours) {
        if (getPos().getBoard().hasAsPosition(pos)) {
            Iterator<Entity> iterator = getPos().getBoard().getAllEntitiesOn(pos).iterator();
            while (iterator.hasNext()) {
                //Somehow this gives a stack overflow error
                iterator.next().getHit();
            }
        }       
    }
    System.out.println(this.toString() + " takes a hit and explodes.");
    getPos().getBoard().removeAsEntity(this);
    terminate();
}

Answer 1

Everytime you call iterator, that will call another iterator that will call another iterator, and so forth. Thus your stack overflow from infinite recursion due to every iterator calling

iterator.next().gethit();

Each iterator will just make a new iterator that needs to go through, but you continue calling getHit() again and again, so you’ll never complete any of the function calls.