[lworld] RFR: 8355227: [lworld] Clarify preview API status for some vallhalla APIs

[Chen Liang]

On Mon, 21 Apr 2025 21:19:21 GMT, Chen Liang <liach at openjdk.org> wrote:

> Per [JEP 12](https://openjdk.org/jeps/12):
> 
>> In order for frameworks to deliver early support for a preview language feature, frameworks should utilize the reflective preview APIs that are co-developed with it. This will allow frameworks to keep up when programs are written to use the permanent version of the language feature.
> 
> According to these rules, the `Objects` methods and the `IdentityException` class themselves must be reflective preview APIs: programs compiled without preview feature dependencies that are running with preview features enabled should be able to access these APIs, as at run-time, they may receive value objects and `IdentityException` thrown by the JVM.
> 
> The only remaining essential preview APIs are the constructors of `IdentityException`: non-preview programs have no reason to construct them.
> 
> In addition, fixed a few JEP feature reference: notably, add reference to [Strict Fields JEP](https://openjdk.org/jeps/8350458).
> 
> Also, made ClassFile API new models reflective preview APIs - class file processors wish to process structures from preview class files even if the current runtime is not in preview. This is already happening to javac and javap.

See thread: https://mail.openjdk.org/pipermail/valhalla-dev/2025-April/014045.html

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PR Comment: https://git.openjdk.org/valhalla/pull/1439#issuecomment-2819536368