RFR: 8266571: Sequenced Collections [v4]

[Stuart Marks]

On Thu, 30 Mar 2023 09:20:16 GMT, Tagir F. Valeev <tvaleev at openjdk.org> wrote:

>> Stuart Marks has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Simplify handling of cached keySet, values, and entrySet views.
>
> src/java.base/share/classes/java/util/SequencedCollection.java line 78:
> 
>> 76:  * @since 21
>> 77:  */
>> 78: public interface SequencedCollection<E> extends Collection<E> {
> 
> Should we narrow the specification for `Collection::add` here, saying that `add` is essentially `addLast`? Specification for deque mentions that `add` and `addLast` are equivalent. Otherwise, the implementation of `SequencedCollection::add` that adds the element to a random position will comply the spec.
> 
> Another thing is `remove(Object)`. Should we specify here that it will remove the first instance of Object inside the collection (like it's specified in the list)? Or is it allowed to return a random one?

`add` isn't the same as `addLast` because things like `SortedSet.add` need to add the element in its proper place. The other subtypes `List`, `Deque`, and `LinkedHashSet` specify that added elements go at the end. But we can't rule out some new collection that might have some reasonable rule for adding a new element other than in the last position.

`List` and `Deque` specify that `remove` removes the first occurrence, but this doesn't apply to `LinkedHashSet` or `SortedSet` since they can have only one occurrence of a matching element. Thus we don't have any obvious examples. But somebody might come up with some new collection for which the first occurrence of duplicate elements isn't the right semantics, so I don't think we want to specify that here.

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PR Review Comment: https://git.openjdk.org/jdk/pull/7387#discussion_r1167371303