RFR: 8358015: Fix SequencedMap sequenced view method specifications [v2]

[Jaikiran Pai]

On Sat, 31 May 2025 00:47:16 GMT, Stuart Marks <smarks at openjdk.org> wrote:

>> For a full explanation, see the bug report [JDK-8358015](https://bugs.openjdk.org/browse/JDK-8358015).
>> 
>> This PR includes three related changes:
>> * New overrides in SequencedMap view collection implementations, which improve their behavior.
>> * Update to `@implSpec` clauses to reflect this behavior (which was previously ill-specified).
>> * Update to a test which relied on unspecified behavior.
>
> Stuart Marks has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Tweak nsee() declaration; adjust specs per suggestion; update copyrights.

Hello Stuart, thank you for the updates. These look good to me.

As for the testing, you are right that behaviour testing where method A calls B and such isn't usually tested in the JDK. I think that's fine. I was unclear about what testing I was talking about in my previous comment. I was mostly curious whether we had tests to verify that the `getFirst()/getLast()` `EntrySet` returned through a `SequencedMap.sequencedEntrySet()` does indeed prevent a `setValue()` call.

I had a look at the existing `BasicMap.java` and it does appear that we already have tests to verify that behaviour (the method `checkUnmodifiableEntry()`). So I think this change has the necessary test coverage.

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Marked as reviewed by jpai (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/25515#pullrequestreview-2884063760