On Tue, 25 Nov 2025 00:31:27 GMT, Chen Liang <[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%
>
> src/java.base/share/classes/java/time/format/Parsed.java line 134:
>
>> 132: if (onlyChronoField) {
>> 133: return new HashMap<>();
>> 134: } else {
>
> Is this condition inverted :thinking: seems like it but how do you get the
> performance numbers
You're right, it's reversed, it's written incorrectly. And this should be in
the constructor, not here. The placement is wrong, but it's still using
EnumMap, so the performance is still improved.
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PR Review Comment: https://git.openjdk.org/jdk/pull/28471#discussion_r2558252666
