RFR: 8319123: Implement JEP 461: Stream Gatherers (Preview) [v14]

[Alan Bateman]

On Thu, 30 Nov 2023 14:30:25 GMT, Viktor Klang <vklang at openjdk.org> wrote:

>> This Pull-Request implements [JEP-461](https://openjdk.org/jeps/461)
>
> Viktor Klang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 32 commits:
> 
>  - Lowering upper boundary of gatherer composition testing to 512
>  - Javadoc clarifications for Gatherer type parameters,
>    correcting descriptions of Integrator type parameters,
>    and more consistently use "initializer function" instead
>    of "supplier function".
>  - Addressing trailing whitespace complaint
>  - Adding @implSpec for Gatherer.andThen, plus adds tests to verify the default impls for Gatherer-related interfaces
>  - Clarifying that Stream#gather is a stateful intermediate operation
>  - Improvements after feedback
>  - Unpacking the rethrown exceptions from Gatherers.mapConcurrent()
>  - Addressing last review feedback
>  - Apply suggestions from code review
>    
>    Integrates Paul Sandoz's feedback/changes
>    
>    Co-authored-by: Paul Sandoz <paul.d.sandoz at googlemail.com>
>  - Minor improvements to Gatherer Javadoc
>  - ... and 22 more: https://git.openjdk.org/jdk/compare/69413690...49c94c7f

Marked as reviewed by alanb (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/16420#pullrequestreview-1757596558