Question

I have an interface – here’s a nicely contrived version as an example:

public interface Particle {      enum Charge {         POSITIVE, NEGATIVE     }      Charge getCharge();      double getMass();      etc... } 

Is there any difference in how implementations of this would behave if I defined the Charge enum as static – i.e. does this have any effect:

public interface Particle {      static enum Charge {         POSITIVE, NEGATIVE     }      Charge getCharge();      double getMass();      etc... } 

Answer 1

No, it makes no difference. However the reason is not because it is a member declaration inside an interface, as Jon says. The real reason is according to language spec (8.9) that

Nested enum types are implicitly static. It is permissable to explicitly declare a nested enum type to be static.

At the following example static does not make any difference either (even though we have no interface):

public class A {   enum E {A,B}; }  public class A {   static enum E {A,B}; } 

Another example with a nested private enum (not implicitly public).

public class A {   private static enum E {A,B} }