This PR optimizes the parsing performance of DateTimeFormatter by replacing HashMap with EnumMap in scenarios where the keys are exclusively ChronoField enum values.
When parsing date/time strings, DateTimeFormatter creates HashMaps to store intermediate parsed values. HashMap has more overhead for operations compared to specialized map implementations. Since ChronoField is an enum and all keys in these maps are ChronoField instances, we can use EnumMap instead, which provides better performance for enum keys due to its optimized internal structure. Parsing scenarios show improvements from 12% to 95% ------------- Commit messages: - bug fix, form @liach - use EnumMap - add benchmark Changes: https://git.openjdk.org/jdk/pull/28471/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28471&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8372460 Stats: 153 lines in 5 files changed: 149 ins; 0 del; 4 mod Patch: https://git.openjdk.org/jdk/pull/28471.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/28471/head:pull/28471 PR: https://git.openjdk.org/jdk/pull/28471
