RFR: 8351443: Improve robustness of StringBuilder

[Shaojin Wen]

On Wed, 30 Apr 2025 14:12:36 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.

src/java.base/share/classes/java/lang/AbstractStringBuilder.java line 1868:

> 1866: 
> 1867:     final boolean isLatin1() {
> 1868:         return COMPACT_STRINGS && coder == LATIN1;

Suggestion:

        return isLatin1(coder);

Can we reuse static isLatin1 like this?

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PR Review Comment: https://git.openjdk.org/jdk/pull/24967#discussion_r2068986449