The DateTimeFormatterBuilder::FIELD_MAP is of type Map<Character, TemporalField>, with key values in the range 'A-Z' and 'a-z'.
We can change the type of FIELD_MAP to an array of length 128 and then use char as an index to access the array. This will reduce the memory usage of DateTimeFormatterBuilder::FIELD_MAP and improve performance slightly. By analyzing the jmap dump memory, we can see that the memory size used by DateTimeFormatterBuilder::FIELD_MAP has dropped from 1.12kb to 528b, the number of objects has decreased and the memory has become more flat. as shown below: * before <img width="2018" height="1016" alt="image" src="https://github.com/user-attachments/assets/57d4c513-55c7-472e-95a8-9f7a4b47662d"; /> * after <img width="1894" height="352" alt="image" src="https://github.com/user-attachments/assets/89cbfb6c-360a-475f-85ea-4365d3b66871"; /> ------------- Commit messages: - @Stable FIELD_MAP Changes: https://git.openjdk.org/jdk/pull/26634/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26634&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8368825 Stats: 29 lines in 1 file changed: 2 ins; 0 del; 27 mod Patch: https://git.openjdk.org/jdk/pull/26634.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/26634/head:pull/26634 PR: https://git.openjdk.org/jdk/pull/26634
