<i18n dev> RFR: 8335366: Improve String.format performance with fastpath [v5]

[David Schlosnagle]

On Mon, 1 Jul 2024 16:28:09 GMT, ExE Boss <duke at openjdk.org> wrote:

>> j.u.Formatter supports args == null
>
> When `args == null` or `args.length == 0`, then the format string can still contain `%%` or `%n`, and those will be formatted to `"%"` and [`System​.lineSeparator()`] respectively.
> 
> [`System​.lineSeparator()`]: https://docs.oracle.com/en/java/javase/22/docs/api/java.base/java/lang/System.html#lineSeparator()

Yeah, if args is null or empty and there are format specifiers in the format string it should throw `IllegalFormatException`. To @liach ’s earlier comments, `String.format` likely needs more exhaustive unit tests covering various positive and negative test cases.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19956#discussion_r1661553502