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. to get the opposite edge of a tile, I want to be able to just type TOP.opposite(). However, when using enums to define these edges I end up having to forward reference at least two of them in the contstructor:

public enum Edge {     TOP(Edge.BOTTOM), //illegal forward reference    BOTTOM(Edge.TOP),    LEFT(Edge.RIGHT), //illegal forward reference    RIGHT(Edge.LEFT);     private Edge opposite;     private Edge(Edge opp){       this.opposite = opp;    }     public Edge opposite(){       return this.opposite;    } } 

Is there any way of getting round this problem using enums which is just as simple?

Answer 1

You can do this which is not as intuitive.

public enum Edge {     TOP, BOTTOM, LEFT, RIGHT;     private Edge opposite;      static {         TOP.opposite = BOTTOM;         BOTTOM.opposite = TOP;         LEFT.opposite = RIGHT;         RIGHT.opposite = LEFT;     }     public Edge opposite(){         return this.opposite;     } }