Anonymous classes of enum constants and var

[David Alayachew]

Idk which is the right group, but I choose amber.

I just want to add a couple of clarifications on the various different
forms (I spend a LOT of my time woth enums).


   - You can use an abstract method like so. It has the benefit of forcing
   every enum value to provide their own implementation of the abstract
   method. Think of it like a switch with no default clause.


enum Blah
{

   VALUE1
   {

      void method()
      {

         println("blah");

      }

   },
   ;

   abstract void method();

}


   - Alternatively, you can provide an implementation of the method. This
   is more like a switch with a default clause.


enum Blah
{

   VALUE1
   {

      void method()
      {

         println("blah");

      }

   },
   ;

   void method()
   {

      println("default");

   }

}


   - And of course, you could model this externally via a switch case. Both
   of the above bullets are modelable as switch expressions (as explained
   already). The benefit is that they can keep the enum simple, but the cost
   is that you must explicitly know the implementation you want instead of
   having one provided for you.




On Wed, Feb 21, 2024, 7:14 AM Pavel Rappo <pavel.rappo at oracle.com> wrote:

> From https://mail.openjdk.org/mailman/listinfo/discuss, this mailing list
> is not suitable for questions like this. I'm not sure which mailing list is
> *the most* suitable, but the following one is surely more suitable:
> https://mail.openjdk.org/pipermail/amber-dev/ (CC'ed).
>
> I believe, the reasons why the first snippet of yours works, but the
> second doesn't, is covered here:
>
>   *
> https://docs.oracle.com/javase/specs/jls/se21/html/jls-8.html#jls-8.9.1
> (like you said)
>   *
> https://docs.oracle.com/javase/specs/jls/se21/html/jls-14.html#jls-14.4.1
>
> I would be surprised if that could change to allow your second snippet.
> That said, if that functionality is truly required, you can provide it
> yourself.
>
> The design of enums allows you to declare a method on an enum class and
> then override it in a particular constant. Alternatively, you can switch on
> an enum constant to provide constant-specific behaviour "externally".
>
> -Pavel
>
> > On 21 Feb 2024, at 10:08, Red IO <redio.development at gmail.com> wrote:
> >
> > I recently tinkered a bit with java enums. While I was researching edge
> features enums support I came across a stackoverflow post referencing the
> JLS 8.9 saying that the optional body of an enum constant is an anonymous
> class declaration.
> > As for some time now methods declared in an anonymous class assigned to
> a var variable are accessible I tried to do the same for the enum constant.
> >
> > var anonymous = new Object() {
> > public void test() {}
> > }
> > anonymous.test(); //works
> >
> >
> > enum Test {
> > A {
> > public void test() {}
> > }
> > }
> > var enumConstant = Test.A;
> > enumConstant.test(); // doesn't work
> >
> > I have a clue to why this doesn't work. It's likely that the type of the
> constant A is the type of the enum and not of the anonymous class.
> >
> > There are some usecases where exclusive methods on enum constants might
> be useful. So it would be nice if this would work.
> >
> > Great regards
> > RedIODev
> >
> >
> >
> >
>
>
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