RFR: 8274898: Cleanup usages of StringBuffer in jdk tools modules

[Andrey Turbanov]

On Thu, 9 Sep 2021 06:53:13 GMT, Andrey Turbanov <duke at openjdk.java.net> wrote:

> StringBuffer is a legacy synchronized class. StringBuilder is a direct replacement to StringBuffer which generally have better performance

> @turbanoff Only [Committers](https://openjdk.java.net/bylaws#committer) are allowed to sponsor changes.

But I am a Committer ��

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PR: https://git.openjdk.java.net/jdk/pull/5433