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From: Lew <lewbloch@gmail.com>
Newsgroups: comp.lang.java.help
Subject: Re: Enum basics
Date: Fri, 4 Nov 2011 20:27:13 -0700 (PDT)
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John B. Matthews wrote:
> Roedy Green wrote:
>> Are enums supposed to support static variables? static methods?
>>=20
>> If the enum is nested in another class, are enum methods supposed to
>> be able to access the containing classes instance variables and
>> methods?
>>=20
>> I believe the answer is "no" to all these questions, but I don't want
>> to lead people astray in my essay on enums.

Nope.

> I believe the answer is yes to all three, as suggested here:

Nope.

And there are only two.  The question of static fields or static methods is=
 the same question.

> <http://java.sun.com/docs/books/jls/third_edition/html/classes.html#8.9>
> <http://stackoverflow.com/questions/1973018>
> <http://groups.google.com/group/comp.lang.java.help/msg/6c3a3d7a27be6331>
>=20
> As a practical matter, I've never had cause to access enclosing class=20
> members from an enum.
>=20
> > You have to communicate with the enum via the initial constructor, or
> > by parms on enum methods.
>=20
> I found it helpful to recall that "An enum type has no instances other=20
> than those defined by its enum constants."

Why *not* read the JLS?  This is exactly the sort of question for which the=
 JLS is the quickest, and yes, the clearest place to find such answers, as =
well as, by definition, the authority.  You already know the JLS exists, yo=
u already know it answers these questions, and there's even a whole freakin=
g section, =A78.9, obscurely entitled "Enums", wherein it states:

"Nested enum types are implicitly static. It is permissable [sic] to explic=
itly declare a nested enum type to be static.
"Discussion
"This implies that it is impossible to define a local (=A714.3) enum, or to=
 define an enum in an inner class (=A78.1.3)."

Boom.  Second question answered.  No, an enum cannot access an enclosing cl=
ass's instance members.  What's the big mystery?

As for the first question, well, enum instances are themselves static membe=
rs of the enum, so it's obvious on the face of it that enums can support st=
atic members.  More subtly, we know that enums are actually classes, and as=
 such can have both static and instance members.

Also, we know that enums inherit from Enum<E>, and that class itself has he=
ritable static members, so we know that enums have static members that are =
not the enum constants.
=00
When in doubt, why not run a simple example up in your favorite development=
 environment?

public enum Foo
{
  /** Foo. */
  FOO,;

  public static final String NON_FOO =3D "Not foo.";
}

Oh, and wouldn't you know it?  The aforementioned obscurely-entitled sectio=
n of the JLS even provides us this example:

enum Color {
  RED, GREEN, BLUE;
  static final Map<String,Color> colorMap =3D=20
     new HashMap<String,Color>();
  static {
    for (Color c : Color.values())
     colorMap.put(c.toString(), c);
  }
}=20

Not only a static member, but a static initializer block!  Woohoo!

So the answer is "yes" to static members and "no" to enclosing-class instan=
ce members.  Ain't the JLS a freaking gold-mine of information?  Answers in=
 a heartbeat!

--=20
Lew
You don't have to be a language lawyer to understand the cited passages, ei=
ther.  Just a programmer.