RFR: 8315850: Improve AbstractMap anonymous Iterator classes [v3]

[Stuart Marks]

On Fri, 8 Sep 2023 16:13:16 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> This PR proposes to slightly improve some iterators of `AbstractMap`:
>> 
>> * Declare two fields `final`
>> * Use distinct classes rather than anonymous classes
>
> Per Minborg has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Fix additional formating issue
>  - Don't use polymorphism and reformat code

Marked as reviewed by smarks (Reviewer).

src/java.base/share/classes/java/util/AbstractMap.java line 901:

> 899: 
> 900:     // Iterator implementations.
> 901:     // Here, we avoid polymorphism to ensure full VM optimization capabilities.

I would remove this comment about avoiding polymorphism, since I think it's a total red herring and is potentially confusing. Otherwise this is fine.

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PR Review: https://git.openjdk.org/jdk/pull/15615#pullrequestreview-1671892215
PR Review Comment: https://git.openjdk.org/jdk/pull/15615#discussion_r1355366295