RFR: JDK-8326908: DecimalFormat::toPattern throws OutOfMemoryError when pattern is empty string [v2]

[Naoto Sato]

On Tue, 5 Mar 2024 00:32:47 GMT, Justin Lu <jlu at openjdk.org> wrote:

>> Please review this PR and corresponding CSR which prevents an OutOfMemoryError by restricting the initial maximum fraction digits for an empty pattern DecimalFormat.
>> 
>> For an empty String pattern DecimalFormat, the maximum fraction digits is initialized to `Integer.MAX_VALUE`. When toPattern() is invoked, StringBuilder internally doubles capacity attempting to append Integer.MAX_VALUE digits until OOME occurs. CSR covers potential behavioral compatibility changes.
>
> Justin Lu has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:
> 
>  - cleanup/typo
>  - Merge branch 'master' into JDK-8326908-emptyPattern-OOME
>  - implement feedback + improve pattern related tests
>  - minor additions
>  - init

src/java.base/share/classes/java/text/DecimalFormat.java line 3367:

> 3365:             }
> 3366:         }
> 3367:         return false;

can simply be a single return statement.

test/jdk/java/text/Format/DecimalFormat/ToPatternTest.java line 60:

> 58:         dFmt.setMinimumFractionDigits(minFrac);
> 59: 
> 60:         String[] patterns = dFmt.toPattern().split("\\.");

Instead of assuming/hardcoding the decimal separator, `DecimalFormatSymbols.getInstance(Locale.US).getDecimalSeparator()` may be better.

test/jdk/java/text/Format/DecimalFormat/ToPatternTest.java line 110:

> 108:     // 8326908: Verify that an empty pattern DecimalFormat does not throw an
> 109:     // OutOfMemoryError when toPattern() is invoked. Behavioral change of
> 110:     // MAXIMUM_INTEGER_DIGITS replaced with DOUBLE_FRACTION_DIGITS for empty

Should we explicitly check `new DecimalFormat("").getMaximumFractionDigits() == DOUBLE_FRACTION_DIGITS`?

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PR Review Comment: https://git.openjdk.org/jdk/pull/18094#discussion_r1513356393
PR Review Comment: https://git.openjdk.org/jdk/pull/18094#discussion_r1513364152
PR Review Comment: https://git.openjdk.org/jdk/pull/18094#discussion_r1513378668