RFR: 6323374: (coll) Optimize Collections.unmodifiable* and synchronized* [v7]

[Ian Graves]

On Thu, 4 Mar 2021 21:37:45 GMT, Joe Darcy <darcy at openjdk.org> wrote:

>> Marked as reviewed by smarks (Reviewer).
>
> If the checks for Navigable set and the like are omitted, I'd prefer to a comment in the sources noting this is intention as a Navigable set is-a Sorted set.

Added comments to the relevant methods noting our intention not to check for subclasses with a little note why.

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PR: https://git.openjdk.java.net/jdk/pull/2596