public interface Room {
  public Room north();
  public Room south();
  public Room east();
  public Room west();
}
 
public enum Rooms implements Room {
  FIRST {
    public Room north() {
      return SECOND;
    }
  },
  SECOND {
    public Room south() {
      return FIRST;
    }
  }
 
  public Room north() { return null; }
  public Room south() { return null; }
  public Room east() { return null; }
  public Room west() { return null; }
}