<i18n dev> RFR: JDK-8326908: DecimalFormat::toPattern throws OutOfMemoryError when pattern is empty string

[Roger Riggs]

On Sat, 2 Mar 2024 00:34:32 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.

src/java.base/share/classes/java/text/DecimalFormat.java line 3717:

> 3715:             // As maxFracDigits are fully displayed unlike maxIntDigits
> 3716:             // Prevent OOME by setting to a much more reasonable value.
> 3717:             setMaximumFractionDigits(DOUBLE_FRACTION_DIGITS);

Setting a reasonable default makes sense.  
In other control paths, the max fraction digits come from the inputs or are explicitly set.

It might be a reasonable related change to use StringBuilder.repeat() instead of a loop at LIne 3312-3319, where the pattern char(s) are being appended to the result.

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PR Review Comment: https://git.openjdk.org/jdk/pull/18094#discussion_r1511404338