RFR: 8272137: Make Collection and Optional classes streamable

[CC007]

On Mon, 9 Aug 2021 12:28:23 GMT, CC007 <github.com+5381337+CC007 at openjdk.org> wrote:

> create Streamable and ParallelStreamable interface and use them in Collection and Optional

The List and Collection interface was almost directly taken from java.util (apart from the small feature interfaces, that I extracted from them), so it would make sense that those classes use an older design.

Are you suggesting that there are deeper architectural issues with the hierarchy-heavy collection stack? Would it be better if a list contained a collection, rather than inheriting from it? If that is the case, anything that is proposed in this PR is merely aiming at symptoms of a possibility much larger underlying problem, which might require going back to the drawing board for all collection related features.

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PR: https://git.openjdk.java.net/jdk/pull/5050