RFR: 8358015: Fix SequencedMap sequenced view method specifications

[Chen Liang]

On Thu, 29 May 2025 00:21:35 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.

src/java.base/share/classes/java/util/AbstractMap.java line 881:

> 879:         UnsupportedOperationException uoe() { return new UnsupportedOperationException(); }
> 880:         // convert null entry return values into NSEE
> 881:         <T> T nsee(T entry) {

Suggestion:

        <T extends Map.Entry<?, ?>> T nsee(T entry) {

So we don't accidentally use this on map keys or values.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25515#discussion_r2115040750