Anonymous classes of enum constants and var

[David Alayachew]

Hold on, I thought this was the entire purpose of refactoring an enum into
a class?

If all of the values do NOT have the same method, then by definition, they
are not of the same type. The nature of an anonymous class is to,
effectively, announce that you are making a new type that, if they are in
the same scope, can use these new things you are defining on the anonymous
type. But, because it is anonymous, then by definition,they have no way to
access this UNLESS THOSE WISHING TO ACCESS ARE IN THE SAME COMPILATION
UNIT. This is scope access.

I think you are complecting the scope access with what abilities the
anonymous class grants you. The anonymous class does not have the ability
to effectively add to its public api. The fact that you can add a public
method to an anonymous class is a very sharp edge that cuts a lot of
developers. Yes, you can put a public method there, but it is almost
entirely redundant. You cannot reference that public method because the
only way to reference that public method is by having the type name. Since
it is anonymous, then by definition, you can't. You must associate that
method to a named type (for example, an interface) in order to be able to
use your new public method. But by that point, it's not your anonymous
class that added to the public api, it's the interface. Very sharp edge
that should be removed in my firm opinion.

At best, anonymous classes can modify the implementation of its public api,
potentially. However, being in the same compilation unit/scope allows you
to view fields and methods that you add to that anonymous class.

Let me know if that doesn't make sense. But by definition, the thing you
are trying to do is not attainable by anonymous classes alone. It would
require some other mechanism to be introduced or used to introduce your
method name into scope. And at that point, it would not be the anonymous
class making this possible.

But maybe I am completely wrong. I spent a couple frustrated months trying
to do exactly what you are doing. Maybe something was added in the past few
releases that made this now possible.

On Wed, Feb 21, 2024, 1:02 PM Red IO <redio.development at gmail.com> wrote:

> This is nice and well. But it isn't the same thing. Sure this works well
> if every varient does exactly the same thing. But say you have a enum
> having varients that share a feature but have their own unique properties.
> Like a rule set to initialize something and an associated constants or
> operation that only makes sense for 1 varient. Currently you need to define
> both public constants and public methods in the enum associating it with
> the whole enum instead of the varient that works with it. In methods that
> gets even worse as you need to provide a default operation that either does
> nothing or throws for incompatible varients. By simply typing the enum
> constant to the anonymous class this would become possible.
>
> Great regards
> RedIODev
>
> On Wed, Feb 21, 2024, 14:49 David Alayachew <davidalayachew at gmail.com>
> wrote:
>
>> 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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