RFR: 8266571: Sequenced Collections

[Chen Liang]

On Tue, 8 Feb 2022 17:23:38 GMT, Stuart Marks <smarks at openjdk.org> wrote:

> PR for Sequenced Collections implementation.

Since we added reversal to deque, can we add notes to a few Collections APIs like `Collections::asLifoQueue` about this newer alternative? Also on using `reverse` on the list view than actually reversing a whole list.

In addition, the new methods should have `@since 20` tags, such as on `LinkedList::reversed`, `SortedSet::addFirst`. Other similar methods are version-tagged, like `Collection::spliterator` or `Method::getParameterCount`.

Is there a particular reason we define poll (null on empty) in SequencedMap but remove (NSEE on empty) in SequencedCollection?

I understand that SequencedCollection doesn't want to be null-ambiguous, and map entries are non-null so poll there is not ambiguous. But I still think using remove for both look more consistent.

Just curious, will sequenced collections be delivered directly or will it incubate/preview first?

src/java.base/share/classes/java/util/Collections.java line 1211:

> 1209:      * @param  s the set for which an unmodifiable view is to be returned.
> 1210:      * @return an unmodifiable view of the specified set.
> 1211:      * @since 20

Extraneous and wrong
Suggestion:

src/java.base/share/classes/java/util/Collections.java line 1248:

> 1246:      * @param  s the set for which an unmodifiable view is to be returned.
> 1247:      * @return an unmodifiable view of the specified sequenced set.
> 1248:      */

Suggestion:

     * @since 20
     */

The last one was misplaced.

src/java.base/share/classes/java/util/Collections.java line 5980:

> 5978:      * an eviction policy, which is not possible with a {@code LinkedHashSet}.
> 5979:      *
> 5980:      * <pre>{@code

Can we upgrade this to a snippet?

src/java.base/share/classes/java/util/SortedSet.java line 303:

> 301:      * @since 20
> 302:      */
> 303:     default E removeFirst() {

Should removeFirst/removeLast be overridden in NavigableSet with a new default implementation like:

    if (this.isEmpty()) {
        throw new NoSuchElementException();
    }
    return this.pollFirst();

which is probably slightly more efficient?

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PR Comment: https://git.openjdk.org/jdk/pull/7387#issuecomment-1253174627
PR Comment: https://git.openjdk.org/jdk/pull/7387#issuecomment-1302239328
PR Comment: https://git.openjdk.org/jdk/pull/7387#issuecomment-1475519496
PR Review Comment: https://git.openjdk.org/jdk/pull/7387#discussion_r1012461962
PR Review Comment: https://git.openjdk.org/jdk/pull/7387#discussion_r1012462289
PR Review Comment: https://git.openjdk.org/jdk/pull/7387#discussion_r1139631921
PR Review Comment: https://git.openjdk.org/jdk/pull/7387#discussion_r1013372259