RFR: 8366178: Implement JEP 526: Lazy Constants (Second Preview) [v25]

[Maurizio Cimadamore]

On Wed, 12 Nov 2025 10:07:39 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> Implement JEP 526: Lazy Constants (Second Preview)
>> 
>> The lazy list/map implementations are broken out from `ImmutableCollections` to a separate class.
>> 
>> The old benchmarks are not moved/renamed to allow comparison with previous releases.
>> 
>> `java.util.Optional` is updated so that its field is annotated with `@Stable`.  This is to allow `Optional` instances to be held in lazy constants and still provide constant folding.
>
> Per Minborg has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 112 commits:
> 
>  - Clarify toString spec
>  - Merge branch 'master' into lazy-constants
>  - Add @AOTSafeClassInitializer
>  - Address comments in PR
>  - Fix merge mistake
>  - Merge master
>  - Rework toString implementations
>  - Update after doc comments
>  - Merge branch 'master' into lazy-constants
>  - Revert the AbstractMap.keySet @Stable annotation
>  - ... and 102 more: https://git.openjdk.org/jdk/compare/76a1109d...1f439bec

src/java.base/share/classes/java/lang/LazyConstant.java line 241:

> 239: 
> 240:     /**
> 241:      * {@return if this lazy constant is the same as the provided {@code obj}}

maybe add (either in this PR or as follow up) a clarification saying that two different lazy constant that point to the same contents are **not** equals

src/java.base/share/classes/java/lang/LazyConstant.java line 280:

> 278:      * {@code computingFunction} at least until initialization completes successfully.
> 279:      * <p>
> 280:      * If the provided computing function is already an instance of

Not sure how I feel about that -- it seems to soft-break equals...

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PR Review Comment: https://git.openjdk.org/jdk/pull/27605#discussion_r2526752889
PR Review Comment: https://git.openjdk.org/jdk/pull/27605#discussion_r2526762818