RFR: 8355536: Model preview enabled VM features in ClassFileFormatVersion [v10]

[Roger Riggs]

On Thu, 26 Feb 2026 03:32:03 GMT, Chen Liang <liach at openjdk.org> wrote:

>> Sometimes, for version-specific feature access APIs, we wish to access the preview features of the current Java SE release. To reduce the impact of adding one preview-specific version on every site, we can add a constant modeling the preview features as a fake version.
>
> Chen Liang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 18 commits:
> 
>  - Tweak test
>  - More tweaks
>  - Refresh
>  - Merge branch 'master' of https://github.com/openjdk/jdk into feature/preview-cffv
>  - Merge branch 'master' of https://github.com/openjdk/jdk into feature/preview-cffv
>  - Fixes
>  - Fix sourceversion test
>  - Merge branch 'master' of https://github.com/openjdk/jdk into feature/preview-cffv
>  - Merge branch 'master' of https://github.com/openjdk/jdk into feature/preview-cffv
>  - Merge branch 'master' of https://github.com/openjdk/jdk into feature/preview-cffv
>  - ... and 8 more: https://git.openjdk.org/jdk/compare/d6044d3e...8e128d29

src/java.base/share/classes/java/lang/reflect/ClassFileFormatVersion.java line 61:

> 59:     /*
> 60:      * Summary of class file format evolution; previews are listed for
> 61:      * convenience, but they are not modeled by the RELEASE_ constants.

Suggestion:

     * convenience, but they are not modeled by the {@code RELEASE_} constants.

Might be a bit more readable.

src/java.base/share/classes/java/lang/reflect/ClassFileFormatVersion.java line 418:

> 416:      * This is a reflective preview API to allow tools running in Java runtime
> 417:      * environments with no preview feature enabled to examine preview VM
> 418:      * features, such as those present in {@code class} files.

I don't think class needs code font.

src/java.base/share/classes/java/lang/reflect/ClassFileFormatVersion.java line 500:

> 498:      */
> 499:     public Runtime.Version runtimeVersion() {
> 500:         if (this == PREVIEW_ENABLED)

Since PREVIEW_ENABLED is for the current version wouldn't it return the same Version string as the running system?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25017#discussion_r2859372408
PR Review Comment: https://git.openjdk.org/jdk/pull/25017#discussion_r2859391900
PR Review Comment: https://git.openjdk.org/jdk/pull/25017#discussion_r2859409739