Illegal Forward Reference and Enums

Question

I\'m programming a game in java which is made up of a grid of tiles. I wan\'t to be able to inuitively define the edges of the tiles and how they relate to each other, e.g.

Answer 1

You could use an internal Map instead to define these associations. This works if at the point of initializing the Map, you already have all enum values created:

public enum Edge {

  TOP,
  BOTTOM,
  LEFT,
  RIGHT;

  private static final Map opposites = 
        new EnumMap(Edge.class);
  static {
    opposites.put(TOP, BOTTOM);
    opposites.put(BOTTOM, TOP);
    opposites.put(LEFT, RIGHT);
    opposites.put(RIGHT, LEFT);
  }

  public Edge opposite(){
    return opposites.get(this);
  }
}