Extending a enum in Java

Question

I have an enum, let's call it A:

public enum A {     A,     B } 

I have a function that takes an enum A:

public void functionA(A enumA) {     //do something } 

How can I create another enum, possibly call B that I can pass to functionA? Something like this?

public enum B {     C }  functionA(B.C); 

I know that you can't extend an enum, but what other options do I have available? What is the best way to achieve this?

Answer 1

You can't.

Enum types are final by design.

The reason is that each enum type should have only the elements declared in the enum (as we can use them in a switch statement, for example), and this is not possible if you allow extending the type.

You might do something like this:

public interface MyInterface {     // add all methods needed here }  public enum A implements MyInterface {     A, B;     // implement the methods of MyInterface }  public enum B implements MyInterface {     C;     // implement the methods of MyInterface } 

Note that it is not possible to do a switch with this interface, then. (Or in general have a switch with an object which could come from more than one enum).