java - Why can't enums be declared locally in a method?

Question

Today, I found myself coding something like this ...

public class LocalEnums {

    public LocalEnums() {
    }

    public void foo() {
        enum LocalEnum {
            A,B,C
        };

        // ....
        // class LocalClass { }

    }
}

and I was kind of surprised when the compiler reported an error on the local enum:

The member enum LocalEnum cannot be local

Why can't enums be declared local like classes?

I found this very useful in certain situations. In the case I was working, the rest of the code didn't need to know anything about the enum.

Is there any structural/design conflict that explains why this is not possible or could this be a future feature of Java?

Answer 1

Enums are static nested classes because they define static member variables (the enum values), and this is disallowed for inner classes: http://docs.oracle.com/javase/specs/jls/se7/html/jls-8.html#jls-8.1.3

Update: I was looking through the JLS (java language specification) for more detail on the restrictions of static nested classes, and didn't find it (although it's probably there, hidden under a different topic). From a pure implementation perspective, there's no reason that this couldn't be done. So I suspect that it was a language philosophy issue: it shouldn't be done, therefore won't be supported. But I wasn't there, so that's pure speculation.

As a comment: if your methods are large enough that they require their own enums, then it's a strong sign that you need refactoring.