java.lang.Object | |||
↳ | java.util.AbstractCollection<E> | ||
↳ | java.util.AbstractQueue<E> | ||
↳ | java.util.concurrent.PriorityBlockingQueue<E> |
An unbounded blocking queue
that uses
the same ordering rules as class PriorityQueue
and supplies
blocking retrieval operations. While this queue is logically
unbounded, attempted additions may fail due to resource exhaustion
(causing OutOfMemoryError). This class does not permit
null elements. A priority queue relying on natural ordering
also does not permit insertion of
non-comparable objects (doing so results in
ClassCastException).
This class and its iterator implement all of the
optional methods of the Collection
and Iterator
interfaces. The Iterator provided in method iterator()
is not guaranteed to traverse the elements of
the PriorityBlockingQueue in any particular order. If you need
ordered traversal, consider using
Arrays.sort(pq.toArray()). Also, method drainTo
can be used to remove some or all elements in priority
order and place them in another collection.
Operations on this class make no guarantees about the ordering of elements with equal priority. If you need to enforce an ordering, you can define custom classes or comparators that use a secondary key to break ties in primary priority values. For example, here is a class that applies first-in-first-out tie-breaking to comparable elements. To use it, you would insert a new FIFOEntry(anEntry) instead of a plain entry object.
class FIFOEntry<E extends Comparable<? super E>> implements Comparable<FIFOEntry<E>> { final static AtomicLong seq = new AtomicLong(); final long seqNum; final E entry; public FIFOEntry(E entry) { seqNum = seq.getAndIncrement(); this.entry = entry; } public E getEntry() { return entry; } public int compareTo(FIFOEntry<E> other) { int res = entry.compareTo(other.entry); if (res == 0 && other.entry != this.entry) res = (seqNum < other.seqNum ? -1 : 1); return res; } }
Public Constructors | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Creates a PriorityBlockingQueue with the default
initial capacity (11) that orders its elements according to
their
natural ordering . | |||||||||||
Creates a PriorityBlockingQueue with the specified
initial capacity that orders its elements according to their
natural ordering . | |||||||||||
Creates a PriorityBlockingQueue with the specified initial
capacity that orders its elements according to the specified
comparator.
| |||||||||||
Creates a PriorityBlockingQueue containing the elements
in the specified collection.
|
Public Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Inserts the specified element into this priority queue.
| |||||||||||
Atomically removes all of the elements from this queue.
| |||||||||||
Returns the comparator used to order the elements in this queue,
or null if this queue uses the
natural ordering of its elements. | |||||||||||
Returns
true if this queue contains the specified element. | |||||||||||
Removes at most the given number of available elements from
this queue and adds them to the given collection.
| |||||||||||
Removes all available elements from this queue and adds them
to the given collection.
| |||||||||||
Returns an iterator over the elements in this queue.
| |||||||||||
Inserts the specified element into this priority queue.
| |||||||||||
Inserts the specified element into this priority queue.
| |||||||||||
Gets but does not remove the element at the head of the queue.
| |||||||||||
Gets and removes the element at the head of the queue, or returns
null if there is no element in the queue. | |||||||||||
Retrieves and removes the head of this queue, waiting up to the
specified wait time if necessary for an element to become available.
| |||||||||||
Inserts the specified element into this priority queue.
| |||||||||||
Always returns Integer.MAX_VALUE because
a PriorityBlockingQueue is not capacity constrained.
| |||||||||||
Removes a single instance of the specified element from this queue,
if it is present.
| |||||||||||
Returns a count of how many objects this
Collection contains. | |||||||||||
Retrieves and removes the head of this queue, waiting if necessary
until an element becomes available.
| |||||||||||
Returns an array containing all of the elements in this queue; the
runtime type of the returned array is that of the specified array.
| |||||||||||
Returns an array containing all of the elements in this queue.
| |||||||||||
Returns the string representation of this
Collection . |
[Expand]
Inherited Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
From class java.util.AbstractQueue
| |||||||||||
From class java.util.AbstractCollection
| |||||||||||
From class java.lang.Object
| |||||||||||
From interface java.lang.Iterable
| |||||||||||
From interface java.util.Collection
| |||||||||||
From interface java.util.Queue
| |||||||||||
From interface java.util.concurrent.BlockingQueue
|
Creates a PriorityBlockingQueue with the default
initial capacity (11) that orders its elements according to
their natural ordering
.
Creates a PriorityBlockingQueue with the specified
initial capacity that orders its elements according to their
natural ordering
.
initialCapacity | the initial capacity for this priority queue |
---|
IllegalArgumentException | if initialCapacity is less than 1 |
---|
Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to the specified comparator.
initialCapacity | the initial capacity for this priority queue |
---|---|
comparator | the comparator that will be used to order this
priority queue. If null , the natural ordering of the elements will be used. |
IllegalArgumentException | if initialCapacity is less than 1 |
---|
Creates a PriorityBlockingQueue containing the elements
in the specified collection. If the specified collection is a
SortedSet
or a PriorityQueue
, this
priority queue will be ordered according to the same ordering.
Otherwise, this priority queue will be ordered according to the
natural ordering
of its elements.
c | the collection whose elements are to be placed into this priority queue |
---|
ClassCastException | if elements of the specified collection cannot be compared to one another according to the priority queue's ordering |
---|---|
NullPointerException | if the specified collection or any of its elements are null |
Inserts the specified element into this priority queue.
e | the element to add |
---|
add(E)
)ClassCastException | if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering |
---|---|
NullPointerException | if the specified element is null |
Atomically removes all of the elements from this queue. The queue will be empty after this call returns.
Returns the comparator used to order the elements in this queue,
or null if this queue uses the natural ordering
of its elements.
Returns true
if this queue contains the specified element.
More formally, returns true
if and only if this queue contains
at least one element e
such that o.equals(e)
.
o | object to be checked for containment in this queue |
---|
Removes at most the given number of available elements from this queue and adds them to the given collection. A failure encountered while attempting to add elements to collection c may result in elements being in neither, either or both collections when the associated exception is thrown. Attempts to drain a queue to itself result in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.
c | the collection to transfer elements into |
---|---|
maxElements | the maximum number of elements to transfer |
Removes all available elements from this queue and adds them to the given collection. This operation may be more efficient than repeatedly polling this queue. A failure encountered while attempting to add elements to collection c may result in elements being in neither, either or both collections when the associated exception is thrown. Attempts to drain a queue to itself result in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.
c | the collection to transfer elements into |
---|
Returns an iterator over the elements in this queue. The
iterator does not return the elements in any particular order.
The returned Iterator is a "weakly consistent"
iterator that will never throw ConcurrentModificationException
, and guarantees to traverse
elements as they existed upon construction of the iterator, and
may (but is not guaranteed to) reflect any modifications
subsequent to construction.
Inserts the specified element into this priority queue.
e | the element to add |
---|
offer(E)
)ClassCastException | if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering |
---|---|
NullPointerException | if the specified element is null |
Inserts the specified element into this priority queue. As the queue is unbounded this method will never block.
e | the element to add |
---|---|
timeout | This parameter is ignored as the method never blocks |
unit | This parameter is ignored as the method never blocks |
ClassCastException | if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering |
---|---|
NullPointerException | if the specified element is null |
Gets but does not remove the element at the head of the queue.
null
if there is
no element in the queue.
Gets and removes the element at the head of the queue, or returns null
if there is no element in the queue.
null
if there is
no element in the queue.
Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.
timeout | how long to wait before giving up, in units of unit |
---|---|
unit | a TimeUnit determining how to interpret the timeout parameter |
InterruptedException |
---|
Inserts the specified element into this priority queue. As the queue is unbounded this method will never block.
e | the element to add |
---|
ClassCastException | if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering |
---|---|
NullPointerException | if the specified element is null |
Always returns Integer.MAX_VALUE because a PriorityBlockingQueue is not capacity constrained.
Removes a single instance of the specified element from this queue,
if it is present. More formally, removes an element e
such
that o.equals(e)
, if this queue contains one or more such
elements. Returns true
if and only if this queue contained
the specified element (or equivalently, if this queue changed as a
result of the call).
o | element to be removed from this queue, if present |
---|
Returns a count of how many objects this Collection
contains.
In this class this method is declared abstract and has to be implemented
by concrete Collection
implementations.
Collection
contains, or Integer.MAX_VALUE
if there are more than Integer.MAX_VALUE
elements in this
Collection
.
Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.
InterruptedException |
---|
Returns an array containing all of the elements in this queue; the runtime type of the returned array is that of the specified array. The returned array elements are in no particular order. If the queue fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this queue.
If this queue fits in the specified array with room to spare (i.e., the array has more elements than this queue), the element in the array immediately following the end of the queue is set to null.
Like the toArray()
method, this method acts as bridge between
array-based and collection-based APIs. Further, this method allows
precise control over the runtime type of the output array, and may,
under certain circumstances, be used to save allocation costs.
Suppose x is a queue known to contain only strings. The following code can be used to dump the queue into a newly allocated array of String:
String[] y = x.toArray(new String[0]);Note that toArray(new Object[0]) is identical in function to toArray().
a | the array into which the elements of the queue are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose |
---|
ArrayStoreException | if the runtime type of the specified array is not a supertype of the runtime type of every element in this queue |
---|---|
NullPointerException | if the specified array is null |
Returns an array containing all of the elements in this queue. The returned array elements are in no particular order.
The returned array will be "safe" in that no references to it are maintained by this queue. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array.
This method acts as bridge between array-based and collection-based APIs.
Returns the string representation of this Collection
. The presentation
has a specific format. It is enclosed by square brackets ("[]"). Elements
are separated by ', ' (comma and space).
Collection
.