RFR : 6799426 : (xs) Add constructor PriorityQueue(Comparator)

[Doug Lea]

On 07/25/13 10:15, Doug Lea wrote:
> On 07/24/13 19:30, Martin Buchholz wrote:
>> PriorityQueue is unusual in that Doug maintains a copy in jsr166 CVS even though
>> it is a non-thread-safe collection.  I think it makes sense,
>> because PriorityQueue and PriorityBlockingQueue have parallel APIs and parallel
>> implementations.  Many changes to one file require a matching change to the
>> other.
>>
>
> The history is that we introduced java.util.concurrent.PriorityBlockingQueue,
> for JDK1.5 which of course led to people wanting plain java.util.PriorityQueue,
> which Josh started working on while at Sun. But for sake of JCP approval,
> we pulled into jsr166 and have adopted ever since, because the two
> classes share code. The capacity constructor was added in JDK1.6,
> but I have no recollection why there is not one with comparator
> but no capacity. It seems reasonable to add one.

Now I remember. Or rather javac forces me to remember.
Adding this constructor breaks source compatibility:

     [javac] /home/dl/concurrent/src/test/tck/PriorityBlockingQueueTest.java:97: 
error: reference to PriorityBlockingQueue is ambiguous
     [javac]             new PriorityBlockingQueue(null);
     [javac]             ^
     [javac]   both constructor PriorityBlockingQueue(Comparator<? super E>) in 
PriorityBlockingQueue and constructor PriorityBlockingQueue(Collection<? extends 
E>) in PriorityBlockingQueue match
     [javac]   where E is a type-variable:
     [javac]     E extends Object declared in class PriorityBlockingQueue


I'm thinking to not include this at least in PriorityBlockingQueue.

-Doug



>
>
>> Regarding this particular change, if PriorityQueue gets a new constructor taking
>> a Comparator, then PriorityBlockingQueue probably should too
>
> Yes.
>
> *** PriorityBlockingQueue.java.~1.99.~    Wed Jul 24 11:23:05 2013
> --- PriorityBlockingQueue.java    Thu Jul 25 10:13:47 2013
> ***************
> *** 200,205 ****
> --- 200,219 ----
>        }
>
>        /**
> +      * Creates a {@code PriorityBlockingQueue} with the default
> +      * initial capacity that orders its elements according to the
> +      * specified comparator.
> +      *
> +      * @param  comparator the comparator that will be used to order this
> +      *         priority queue.  If {@code null}, the {@linkplain Comparable
> +      *         natural ordering} of the elements will be used.
> +      * @since 1.8
> +      */
> +     public PriorityBlockingQueue(Comparator<? super E> comparator) {
> +         this(DEFAULT_INITIAL_CAPACITY, comparator);
> +     }
> +
> +     /**
>         * Creates a {@code PriorityBlockingQueue} containing the elements
>         * in the specified collection.  If the specified collection is a
>         * {@link SortedSet} or a {@link PriorityQueue}, this
>
>