On Tue, 9 Dec 2025 10:02:36 GMT, Shaojin Wen <[email protected]> wrote:
>> 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%
>
> Shaojin Wen has updated the pull request incrementally with one additional
> commit since the last revision:
>
> remove redundant checkField
src/java.base/share/classes/java/time/format/Parsed.java line 175:
> 173: */
> 174: @SuppressWarnings("unchecked")
> 175: Parsed(boolean onlyChronoField) {
If you know that only ChronoFields are used then imho the loop over the entries
of `fieldValues` in method `resolveFields` can be skipped (line 290ff).
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PR Review Comment: https://git.openjdk.org/jdk/pull/28471#discussion_r2626170333
