RFR: 8366224: Introduce DecimalDigits.appendPair for efficient two-digit formatting and refactor DateTimeHelper [v18]

[Chen Liang]

On Thu, 13 Nov 2025 04:07:45 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> This PR introduces a new efficient API for appending two-digit integers to StringBuilders and refactors DateTimeHelper to leverage this new functionality.
>> 
>> Changes include:
>> 
>> 1. New `appendPair` method for efficient two-digit integer formatting (00-99):
>>    - Added `AbstractStringBuilder.appendLatin1(char c1, char c2)` with core implementation
>>    - Added `JavaLangAccess.appendPair(StringBuilder, char c1, char c2)` for internal access
>>    - Added `DecimalDigits.appendPair(StringBuilder, int)` public static utility method
>>    - Enhanced Javadoc documentation for all new methods
>> 
>> 2. Refactored `DateTimeHelper` to use the new `DecimalDigits.appendPair`:
>>    - Updated `DateTimeHelper.formatTo` methods for `LocalDate` and `LocalTime`
>>    - Replaced manual formatting logic with the new efficient two-digit appending
>>    - Improved code clarity and consistency in date/time formatting
>> 
>> These changes improve code clarity and performance when formatting two-digit numbers, particularly in date/time formatting scenarios.
>
> Shaojin Wen has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - fix codestyle
>  - digitQuad MergeStore & from @liach

test/jdk/jdk/internal/util/DecimalDigitsTest.java line 36:

> 34:  * @summary Test DecimalDigits.appendPair method with LATIN1 and UTF16 encoding
> 35:  * @modules java.base/jdk.internal.util
> 36:  * @run testng test.jdk.internal.util.DecimalDigitsTest

We recommend using junit for new tests.

test/jdk/jdk/internal/util/DecimalDigitsTest.java line 41:

> 39: 
> 40:     @Test
> 41:     public void testAppendPair() {

This duplicates testAppendPairWithLatin1Encoding and can be removed.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26911#discussion_r2521325209
PR Review Comment: https://git.openjdk.org/jdk/pull/26911#discussion_r2521324512