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I'm working with a very large grid-based world that has around 50-90% of its grid spaces empty at any given time, therefore I chose to use a HashMap over an array.

The problem is that basic interactions don't seem to be working right, and I think it's because of some disconnect between the position the hashmap is using as a key and position as the grid object knows it.

These are the problems I'm having:

  • object's ability to detect its neighbors is unreliable
  • object deletion is unreliable

Here is the code:

The getNeighbors method of GridObject:

public ArrayList<GridObject> getNeighbors()
{
  ArrayList<GridObject> neighbors = new ArrayList<GridObject>(8);
  final int[] d = {-1, 0, 1};
  for(int i : d)
    for(int j : d)
      if(j != 0 || i != 0) // Don't use (0, 0)
      {        // Manager is just a wrapper for the HashMap; treat this like HashMap.get()
        GridObject p = manager.get(location.x + i, location.y + j);
    if(p != null) neighbors.add(p);
      }
  return neighbors;
}

This is from the update method of the Manager class. MarkedForRemoval is a java.util.Stack of Points that is populated by GridObject s that call Manager.markForRemoval(), which just pushes a passed point into the stack. update() runs once a frame:

public void update()
{
    // libgdx graphics stuff
    renderTarget.setColor(new Color(0f, 0f, 0f, 0f));
    renderTarget.fill();

    for(GridObject p : map.values())
    {
      renderTarget.drawPixel(p.location.x, p.location.y, Color.rgba8888(p.team.getColor()));
      p.update();
    }
    while(!markedForRemoval.isEmpty())
      map.remove(markedForRemoval.pop());
    }

And this is the Manager.put() method, which is the only way that new GridObjects are added:

public GridObject put(int x, int y)
{
  final Point p = new Point(x, y);
  return map.put(p, new GridObject(this, p));
}

And finally the Manager.get() method:

public GridObject get(int x, int y)
{
  return get(new Point(x, y));
}

I am using java.awt.Point to store the locations, which has both Objects.equals() and Object.hashCode() implemented correctly, as far as I know.

I am lost as to where I have gone wrong.

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