RFR: 8351443: Improve robustness of StringBuilder [v6]

[Brent Christian]

On Tue, 6 May 2025 15:23:39 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

>> Refactor AbstractStringBuilder to maintain consistency among count, coder, and value buffers while the buffer capacity is being expanded and/or inflated from Latin1 to UTF16 representations. 
>> The refactoring pattern is to read and write AbstractStringBuilder fields once using locals for all intermediate values. 
>> Support methods are static, designed to pass all values as arguments and return a value.
>> 
>> The value byte array is reallocated under 3 conditions:
>> - Increasing the capacity with the same encoder
>> - Increasing the capacity and inflation to change the coder from LATIN1 to UTF16
>> - Inflation with the same capacity
>> 
>> Added StressSBTest to exercise public instance methods of StringBuilder.
>
> Roger Riggs has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Apply reviewer suggestions for typos, javadoc, and copyright dates.

src/java.base/share/classes/java/lang/AbstractStringBuilder.java line 2044:

> 2042:      * @param s a string
> 2043:      * @param off the offset of the first character to append
> 2044:      * @param end end last (exclusive) character to append

It might be helpful to somehow clarify that, in the case of appending Latin1 characters to a Latin1 buffer, it is expected/required that `value` is already of sufficient size.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24967#discussion_r2076475596