Can enums be subclassed to add new elements?

Question

I want to take an existing enum and add more elements to it as follows: enum A {a,b,c} enum B extends A {d} // B is {a,b,c,d} Is this possible in Java?

Answer 1

Hi - no, you cannot - view an enum as sort of a final Class ...

I believe the Java compiler applies some auto-magic to declared enums - e.g.,

public enum Direction {

NORTH, EAST, SOUTH, WEST ;

}

I believe it implicitly extends java.lang.Enum - and so you can't extend another Class or Enum since the language doesn't support multiple inheritance.

I understand why you're asking. It would be nice to declare the following given the above enum

public enum MapDirection extends Direction {

NORTHEAST, SOUTHWEST, NORTHWEST, SOUTHEAST;

}

I'll let you know if I find a clever way to reuse/extend the definition of an existing enum ...

--Lou