RFR: 8305457: Implement java.io.IO [v7]

[Per Minborg]

On Tue, 7 May 2024 20:23:11 GMT, Pavel Rappo <prappo at openjdk.org> wrote:

>>> Should this be final?
>> 
>> With only the private constructor, it doesn't matter too much in practice, but an explicit `final` would be good documentation if that is the intent.
>
> If the sole constructor of a class is private, not only does it preclude the class from being instantiated, but it also precludes the class from being extended. Mind you, even with the sole private constructor, both instantiation and extension are still possible from inside the class or its nested classes. As long as we don't leak such instances to API clients, they won't seem to be able to observe any difference between "the private constructor" and "the private constructor of a final class".
> 
> I think that just having that constructor private but the class "non-final" makes bigger bang for the buck. We can defer the decision to make the class final.
> 
> If this helps, here are a few well-known similar classes:
> 
>   - java.util.Collections
>   - java.util.concurrent.Executors

Although true (and also described in Item 4 in "Effective Java" 3rd ed by JB) I think it is better to also signal the intent by marking the class as `final`. See for example Arrays that we updated some time ago.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19112#discussion_r1596377720