RFR: 8284637: Improve String.join performance

[Claes Redestad]

On Fri, 8 Apr 2022 19:33:26 GMT, XenoAmess <duke at openjdk.java.net> wrote:

> 8284637: Improve String.join performance

I think you can use or extend the existing `org.openjdk.bench.java.util.StringJoinerBench` JMH for this.

Refer to [doc/testing.md](../tree/master/doc/testing.md) for setup help, but you should be able to run specific JMH using the build system with something like `make test TEST=micro:StringJoinerBench.join`

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PR: https://git.openjdk.java.net/jdk/pull/8169