On Wed, 27 Aug 2025 17:57:31 GMT, Roger Riggs <rri...@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.appendPair(int i)` with core implementation
>> - Added `JavaLangAccess.appendPair(StringBuilder, int)` for internal
>> access
>> - Added `System.JavaLangAccessImpl.appendPair(StringBuilder, int)` bridge
>> - 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.
>
> Generally, even with the performance benefits, this code is too narrow a use
> case to justify the hacking into AbstractStringBuilder and adding another
> package busting JavaLangAccess entry point.
Thank you for your feedback, @RogerRiggs.
I introduced this PR because I plan to optimize the performance of
`java.time.format.DateTimeFormatter`'s `parse` and `format` methods. This is a
very large change, and to facilitate code review, I am splitting the process
into multiple smaller PRs. This allows us to achieve continuous improvement,
and this PR is one part of that effort.
In future optimizations, I need to use `AbstractStringBuilder.appendPair` when
writing values like Year/Month/DayOfMonth/Hour/Minute/Second within the
`java.time.format.DateTimeFormatterBuilder$NumberPrinterParser#format` method.
In the current PR, using `appendPair` in `DateTimeHelper` to write
month/dayOfMonth/hour/minute/second results in code that is more intuitive than
the original.
* Original
month = date.getMonthValue(),
day = date.getDayOfMonth();
buf.append(month < 10 ? "-0" : "-").append(month)
.append(day < 10 ? "-0" : "-").append(day);
* Improved
buf.append('-');
DecimalDigits.appendPair(buf, date.getMonthValue());
buf.append('-');
DecimalDigits.appendPair(buf, date.getDayOfMonth());
The improved code is more readable than the original.
Placing `appendPair` in `DecimalDigits` alongside other `putPair` series
methods also makes the code's purpose easier to understand.
`AbstractStringBuilder.appendPair` was introduced for the `java.time` format
scenario, but it can also be used in `java.util.Formatter` in the future, or
potentially with `StringTemplate` if it's introduced. My latest commit adds
more usage scenarios in `core-libs`.
-------------
PR Comment: https://git.openjdk.org/jdk/pull/26911#issuecomment-3231113907
