RFR: 8339260: Move rarely used constants out of ClassFile [v6]

[Adam Sotona]

On Tue, 10 Sep 2024 21:18:19 GMT, Chen Liang <liach at openjdk.org> wrote:

>> Many constants are cluttered in `ClassFile`. However, only a few of them are ever used by regular users, most notably `ACC_` flags and `JAVA_X_VERSION` constants. All other constants are specific and should live in more local locations, such as getters that return these constants.
>> 
>> This simplification of `ClassFile` constants improves user onramp to the Class-File API.
>> 
>> Notably, before, if `ClassFile` is static imported, `Opcode` enums must be qualified due to name clashes; this relocation allows `Opcode` enums to be static imported with `ACC_` flags, improving class file writing user experience.
>
> Chen Liang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 14 commits:
> 
>  - Merge branch 'master' of https://github.com/openjdk/jdk into fix/constant-moving
>  - omission in tests
>  - Merge branch 'master' of https://github.com/openjdk/jdk into fix/constant-moving
>  - Rename constants at new locations, link to related factories, cp tag constant names
>  - Fix compile errors
>  - Merge branch 'master' of https://github.com/openjdk/jdk into fix/constant-moving
>  - Merge branch 'master' of https://github.com/openjdk/jdk into fix/constant-moving
>  - Merge branch 'master' of https://github.com/openjdk/jdk into fix/constant-moving
>  - Compile errors; now tests are all green.
>  - Move Constant Pool tags to PoolEntry
>    
>    Two unexpected usages in jlink raw processing, but rest is fine
>  - ... and 4 more: https://git.openjdk.org/jdk/compare/6fd043f1...fa9ea36d

src/java.base/share/classes/java/lang/classfile/Opcode.java line 1133:

> 1131:      */
> 1132:     @PreviewFeature(feature = PreviewFeature.Feature.CLASSFILE_API)
> 1133:     public static final class OpcodeValues {

I think we should not introduce a new API class just to expose int constants we plan to hide under the Opcode.
My proposal is to hard-code the opcodes in the Opcode initialization and remove OpcodeValues class.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20773#discussion_r1771654912