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

enum Edge {
    TOP {
        @Override
        public Edge opposite() {
            return BOTTOM;
        }
    },
    BOTTOM {
        @Override
        public Edge opposite() {
            return TOP;
        }
    },
    LEFT {
        @Override
        public Edge opposite() {
            return RIGHT;
        }
    },
    RIGHT {
        @Override
        public Edge opposite() {
            return LEFT;
        }
    };

    public abstract Edge opposite();
}