RFR: 8188055: (ref) Add Reference::refersTo predicate [v3]

[Daniel Fuchs]

On Wed, 14 Oct 2020 18:09:16 GMT, Mandy Chung <mchung at openjdk.org> wrote:

>> @mlchung  I have often used a `Reference<?>` in tests - but my main usage there would be to call `ref.refersTo(null)`
>> which works in all cases. My main concern here however is that using `T` in `refersTo` seems to go against the
>> advertised usage of the method - I mean - if I have an object `obj` of type unknown, I can always do `obj == ref.get()`
>> whatever the parameter type of `ref` is. But I won't be able to call `ref.refersTo(obj)` unless I use raw types and
>> suppress warnings. So I just wanted to check that this was intentional.
>
> For the common cases, the application should know the type of the referent and using `T` in `refersTo` will benefit
> from the compiler type checking.   For the unknown type case, cast to `Reference<Object>` is not ideal but reasonable?
> something like this:  Reference<Object> r = (Reference<Object>) ref;
> r.refersTo(obj);

That sounds reasonable to me. Thanks for looking into it.

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PR: https://git.openjdk.java.net/jdk/pull/498