RFR: 6356745: (coll) Add PriorityQueue(Collection, Comparator) [v4]

[Stuart Marks]

On Tue, 19 Dec 2023 21:17:02 GMT, Valeh Hajiyev <duke at openjdk.org> wrote:

>> This commit addresses the current limitation in the `PriorityQueue` implementation, which lacks a constructor to efficiently create a priority queue with a custom comparator and an existing collection. In order to create such a queue, we currently need to initialize a new queue with custom comparator, and after that populate the queue using `addAll()` method, which in the background calls `add()` method (which takes `O(logn)` time) for each element of the collection (`n` times).  This is resulting in an overall time complexity of `O(nlogn)`. 
>> 
>> 
>> PriorityQueue<String> pq = new PriorityQueue<>(customComparator);
>> pq.addAll(existingCollection);
>> 
>> 
>> The pull request introduces a new constructor to streamline this process and reduce the time complexity to `O(n)`.  If you create the queue above using the new constructor, the contents of the collection will be copied (which takes `O(n)` time) and then later  `heapify()` operation (Floyd's algorithm) will be called once (another `O(n)` time). Overall the operation will be reduced from `O(nlogn)` to `O(2n)` -> `O(n)` time.
>> 
>> 
>> PriorityQueue<String> pq = new PriorityQueue<>(existingCollection, customComparator);
>
> Valeh Hajiyev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   updated the javadoc

src/java.base/share/classes/java/util/PriorityQueue.java line 216:

> 214:      * specified collection. The {@code PriorityQueue} will order the
> 215:      * priority queue's elements elements according to the specified
> 216:      * comparator.

I know you updated this in response to Alan's comment, but the second sentence now says "elements elements". And repeating "priority queue" sounds somewhat redundant. Suggestion for the second sentence:

> The elements of the new {@code PriorityQueue} will be ordered according to
> the specified comparator.

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PR Review Comment: https://git.openjdk.org/jdk/pull/17045#discussion_r1432255396