Nested Java enum definition - does declaring as static make a difference? [duplicate]

问题

This question already has answers here:

In Java, are enum types inside a class static? (2 answers)

Closed 3 years ago.

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...
}

回答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}
}

回答2:

No, it makes no difference. From the language spec, section 9.5:

Interfaces may contain member type declarations (§8.5). A member type declaration in an interface is implicitly static and public.

来源：https://stackoverflow.com/questions/253226/nested-java-enum-definition-does-declaring-as-static-make-a-difference