why enums only on a top level class or interface?

Question

I am studying Java and wrote a very simple program. In it I can put enums in the top most level, but not inside a method. The way I see it, enums are almost like constants, so why not use them inside methods?

In my program, enum1 is allowed, but enum2 is not. Why?

enum enum1 {A, B, C};

public static void main(String[] args)
{
    enum enum2 {A, B, C};  // only on a top level class or interface
}

See this thread http://stackoverflow.com/questions/11026626/why-java-doesnt-allow-to-define-enum-within-a-method — nicko, Jun 17 '14 at 20:37
So, you are just pointing to another question which says that they don't know what is the reason.... — Cindy Langdon, Jun 17 '14 at 20:56
@user2864740 But WHY? It is the same thing as saying that you can have any color, except BLUE. — Cindy Langdon, Jun 17 '14 at 20:57
@user2864740 Not entirely true; classes *can* be defined inside methods. (Try it!). — Jesper, Jun 17 '14 at 21:09
@user2864740 Yes, it's a little-known feature, and almost nobody uses it, but it's possible. — Jesper, Jun 17 '14 at 21:13
**Update:** Local enums, defined within a method, will be a feature in Java 16, previewing in Java 15. See: [*JEP 384: Records (Second Preview)*](https://openjdk.java.net/jeps/384). Discussed in [my Answer](https://stackoverflow.com/a/62807591/642706) on another page. — Basil Bourque, Jul 09 '20 at 05:03

score 8 · Answer 1 · edited Jun 17 '14 at 20:38

8

Because enums are a special type of class definition.

This doc describes some information about special things the compiler does including adding static methods (valueOf). While you could declare an anonymous class withing the context of a method, it could not have static methods.

edited Jun 17 '14 at 20:38

jmj

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answered Jun 17 '14 at 20:36

Brett Okken

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score 3 · Answer 2 · answered Jun 17 '14 at 20:37

3

It may have to do with the fact that Enums are compiled similarly to classes. For the same reason you cannot declare a class definition inside a method, you cannot declare in enum either.

answered Jun 17 '14 at 20:37

Adam Yost

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But you can declare classes inside a method. Granted, they are anonymous classes, but they are still declared inside a method. – Epiglottal Axolotl Jun 17 '14 at 20:37
These are non-anonymous. @Brett Okken linked the documentation is his answer. – Adam Yost Jun 17 '14 at 20:39
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Never said they weren't - just making a point of clarification. – Epiglottal Axolotl Jun 17 '14 at 21:04
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@Stendika It's a little-known feature of Java, but you *can* actually define non-anonymous classes inside methods. Try it yourself... – Jesper Jun 17 '14 at 21:11

score 1 · Answer 3 · answered Jun 17 '14 at 20:38

1

Enums in Java are actually creating a class, which causes them to have limitations like this.

http://docs.oracle.com/javase/tutorial/java/javaOO/enum.html

answered Jun 17 '14 at 20:38

John C

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score 0 · Answer 4 · answered Jun 17 '14 at 20:37

Enumerations are way more than constant, you can create constructor for them. They are like Classes, you can't define a class in a method, it's the same for enumeration. If you want constant, you should better consider using final static var

why enums only on a top level class or interface?

4 Answers4