RFR: 8287695: Use String.contains() instead of String.indexOf() in jdk.hotspot.agent

[Andrey Turbanov]

On Wed, 1 Jun 2022 07:52:50 GMT, Andrey Turbanov <aturbanov at openjdk.org> wrote:

> `String.contains` was introduced in Java 5.
> Some code in jdk.hotspot.agent still uses old approach with `String.indexOf` to check if String contains specified substring.
> I propose to migrate such usages. Makes code shorter and easier to read.

All green. Thank you for review!

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PR: https://git.openjdk.java.net/jdk/pull/8966