Class PriorityBlockingQueue<E>
- Type Parameters:
E
- the type of elements held in this queue
- All Implemented Interfaces:
Serializable
,Iterable<E>
,Collection<E>
,BlockingQueue<E>
,Queue<E>
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()
and the
Spliterator provided in method spliterator()
are 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>> {
static final 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;
}
}
This class is a member of the Java Collections Framework.
- Since:
- 1.5
- See Also:
-
Constructor Summary
ConstructorDescriptionCreates aPriorityBlockingQueue
with the default initial capacity (11) that orders its elements according to their natural ordering.PriorityBlockingQueue
(int initialCapacity) Creates aPriorityBlockingQueue
with the specified initial capacity that orders its elements according to their natural ordering.PriorityBlockingQueue
(int initialCapacity, Comparator<? super E> comparator) Creates aPriorityBlockingQueue
with the specified initial capacity that orders its elements according to the specified comparator.PriorityBlockingQueue
(Collection<? extends E> c) Creates aPriorityBlockingQueue
containing the elements in the specified collection. -
Method Summary
Modifier and TypeMethodDescriptionboolean
Inserts the specified element into this priority queue.void
clear()
Atomically removes all of the elements from this queue.Comparator
<? super E> Returns the comparator used to order the elements in this queue, ornull
if this queue uses the natural ordering of its elements.boolean
Returnstrue
if this queue contains the specified element.int
drainTo
(Collection<? super E> c) Removes all available elements from this queue and adds them to the given collection.int
drainTo
(Collection<? super E> c, int maxElements) Removes at most the given number of available elements from this queue and adds them to the given collection.void
Performs the given action for each element of theIterable
until all elements have been processed or the action throws an exception.iterator()
Returns an iterator over the elements in this queue.boolean
Inserts the specified element into this priority queue.boolean
Inserts the specified element into this priority queue.peek()
Retrieves, but does not remove, the head of this queue, or returnsnull
if this queue is empty.poll()
Retrieves and removes the head of this queue, or returnsnull
if this queue is empty.Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.void
Inserts the specified element into this priority queue.int
Always returnsInteger.MAX_VALUE
because aPriorityBlockingQueue
is not capacity constrained.boolean
Removes a single instance of the specified element from this queue, if it is present.boolean
removeAll
(Collection<?> c) Removes all of this collection's elements that are also contained in the specified collection (optional operation).boolean
Removes all of the elements of this collection that satisfy the given predicate (optional operation).boolean
retainAll
(Collection<?> c) Retains only the elements in this collection that are contained in the specified collection (optional operation).int
size()
Returns the number of elements in this collection.Returns aSpliterator
over the elements in this queue.take()
Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.Object[]
toArray()
Returns an array containing all of the elements in this queue.<T> T[]
toArray
(T[] a) Returns an array containing all of the elements in this queue; the runtime type of the returned array is that of the specified array.Methods declared in class java.util.AbstractQueue
addAll, element, remove
Methods declared in class java.util.AbstractCollection
containsAll, isEmpty, toString
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Methods declared in interface java.util.Collection
addAll, containsAll, equals, hashCode, isEmpty, parallelStream, stream, toArray
-
Constructor Details
-
PriorityBlockingQueue
public PriorityBlockingQueue()Creates aPriorityBlockingQueue
with the default initial capacity (11) that orders its elements according to their natural ordering. -
PriorityBlockingQueue
public PriorityBlockingQueue(int initialCapacity) Creates aPriorityBlockingQueue
with the specified initial capacity that orders its elements according to their natural ordering.- Parameters:
initialCapacity
- the initial capacity for this priority queue- Throws:
IllegalArgumentException
- ifinitialCapacity
is less than 1
-
PriorityBlockingQueue
Creates aPriorityBlockingQueue
with the specified initial capacity that orders its elements according to the specified comparator.- Parameters:
initialCapacity
- the initial capacity for this priority queuecomparator
- the comparator that will be used to order this priority queue. Ifnull
, the natural ordering of the elements will be used.- Throws:
IllegalArgumentException
- ifinitialCapacity
is less than 1
-
PriorityBlockingQueue
Creates aPriorityBlockingQueue
containing the elements in the specified collection. If the specified collection is aSortedSet
or aPriorityBlockingQueue
, 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.- Parameters:
c
- the collection whose elements are to be placed into this priority queue- Throws:
ClassCastException
- if elements of the specified collection cannot be compared to one another according to the priority queue's orderingNullPointerException
- if the specified collection or any of its elements are null
-
-
Method Details
-
add
Inserts the specified element into this priority queue.- Specified by:
add
in interfaceBlockingQueue<E>
- Specified by:
add
in interfaceCollection<E>
- Specified by:
add
in interfaceQueue<E>
- Overrides:
add
in classAbstractQueue<E>
- Parameters:
e
- the element to add- Returns:
true
(as specified byCollection.add(E)
)- Throws:
ClassCastException
- if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's orderingNullPointerException
- if the specified element is null
-
offer
Inserts the specified element into this priority queue. As the queue is unbounded, this method will never returnfalse
.- Specified by:
offer
in interfaceBlockingQueue<E>
- Specified by:
offer
in interfaceQueue<E>
- Parameters:
e
- the element to add- Returns:
true
(as specified byQueue.offer(E)
)- Throws:
ClassCastException
- if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's orderingNullPointerException
- if the specified element is null
-
put
Inserts the specified element into this priority queue. As the queue is unbounded, this method will never block.- Specified by:
put
in interfaceBlockingQueue<E>
- Parameters:
e
- the element to add- Throws:
ClassCastException
- if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's orderingNullPointerException
- if the specified element is null
-
offer
Inserts the specified element into this priority queue. As the queue is unbounded, this method will never block or returnfalse
.- Specified by:
offer
in interfaceBlockingQueue<E>
- Parameters:
e
- the element to addtimeout
- This parameter is ignored as the method never blocksunit
- This parameter is ignored as the method never blocks- Returns:
true
(as specified byBlockingQueue.offer
)- Throws:
ClassCastException
- if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's orderingNullPointerException
- if the specified element is null
-
poll
-
take
Description copied from interface:BlockingQueue
Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.- Specified by:
take
in interfaceBlockingQueue<E>
- Returns:
- the head of this queue
- Throws:
InterruptedException
- if interrupted while waiting
-
poll
Description copied from interface:BlockingQueue
Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.- Specified by:
poll
in interfaceBlockingQueue<E>
- Parameters:
timeout
- how long to wait before giving up, in units ofunit
unit
- aTimeUnit
determining how to interpret thetimeout
parameter- Returns:
- the head of this queue, or
null
if the specified waiting time elapses before an element is available - Throws:
InterruptedException
- if interrupted while waiting
-
peek
-
comparator
Returns the comparator used to order the elements in this queue, ornull
if this queue uses the natural ordering of its elements.- Returns:
- the comparator used to order the elements in this queue,
or
null
if this queue uses the natural ordering of its elements
-
size
public int size()Description copied from interface:Collection
Returns the number of elements in this collection. If this collection contains more thanInteger.MAX_VALUE
elements, returnsInteger.MAX_VALUE
.- Specified by:
size
in interfaceCollection<E>
- Returns:
- the number of elements in this collection
-
remainingCapacity
public int remainingCapacity()Always returnsInteger.MAX_VALUE
because aPriorityBlockingQueue
is not capacity constrained.- Specified by:
remainingCapacity
in interfaceBlockingQueue<E>
- Returns:
Integer.MAX_VALUE
always
-
remove
Removes a single instance of the specified element from this queue, if it is present. More formally, removes an elemente
such thato.equals(e)
, if this queue contains one or more such elements. Returnstrue
if and only if this queue contained the specified element (or equivalently, if this queue changed as a result of the call).- Specified by:
remove
in interfaceBlockingQueue<E>
- Specified by:
remove
in interfaceCollection<E>
- Overrides:
remove
in classAbstractCollection<E>
- Parameters:
o
- element to be removed from this queue, if present- Returns:
true
if this queue changed as a result of the call
-
contains
Returnstrue
if this queue contains the specified element. More formally, returnstrue
if and only if this queue contains at least one elemente
such thato.equals(e)
.- Specified by:
contains
in interfaceBlockingQueue<E>
- Specified by:
contains
in interfaceCollection<E>
- Overrides:
contains
in classAbstractCollection<E>
- Parameters:
o
- object to be checked for containment in this queue- Returns:
true
if this queue contains the specified element
-
drainTo
Description copied from interface:BlockingQueue
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 collectionc
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 inIllegalArgumentException
. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.- Specified by:
drainTo
in interfaceBlockingQueue<E>
- Parameters:
c
- the collection to transfer elements into- Returns:
- the number of elements transferred
- Throws:
UnsupportedOperationException
- if addition of elements is not supported by the specified collectionClassCastException
- if the class of an element of this queue prevents it from being added to the specified collectionNullPointerException
- if the specified collection is nullIllegalArgumentException
- if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection
-
drainTo
Description copied from interface:BlockingQueue
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 collectionc
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 inIllegalArgumentException
. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.- Specified by:
drainTo
in interfaceBlockingQueue<E>
- Parameters:
c
- the collection to transfer elements intomaxElements
- the maximum number of elements to transfer- Returns:
- the number of elements transferred
- Throws:
UnsupportedOperationException
- if addition of elements is not supported by the specified collectionClassCastException
- if the class of an element of this queue prevents it from being added to the specified collectionNullPointerException
- if the specified collection is nullIllegalArgumentException
- if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection
-
clear
public void clear()Atomically removes all of the elements from this queue. The queue will be empty after this call returns.- Specified by:
clear
in interfaceCollection<E>
- Overrides:
clear
in classAbstractQueue<E>
-
toArray
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.
- Specified by:
toArray
in interfaceCollection<E>
- Overrides:
toArray
in classAbstractCollection<E>
- Returns:
- an array containing all of the elements in this queue
-
toArray
public <T> T[] toArray(T[] a) 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 ofString
:String[] y = x.toArray(new String[0]);
toArray(new Object[0])
is identical in function totoArray()
.- Specified by:
toArray
in interfaceCollection<E>
- Overrides:
toArray
in classAbstractCollection<E>
- Type Parameters:
T
- the component type of the array to contain the collection- Parameters:
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- Returns:
- an array containing all of the elements in this queue
- Throws:
ArrayStoreException
- if the runtime type of the specified array is not a supertype of the runtime type of every element in this queueNullPointerException
- if the specified array is null
-
iterator
Returns an iterator over the elements in this queue. The iterator does not return the elements in any particular order.The returned iterator is weakly consistent.
- Specified by:
iterator
in interfaceCollection<E>
- Specified by:
iterator
in interfaceIterable<E>
- Specified by:
iterator
in classAbstractCollection<E>
- Returns:
- an iterator over the elements in this queue
-
spliterator
Returns aSpliterator
over the elements in this queue. The spliterator does not traverse elements in any particular order (theORDERED
characteristic is not reported).The returned spliterator is weakly consistent.
The
Spliterator
reportsSpliterator.SIZED
andSpliterator.NONNULL
.- Specified by:
spliterator
in interfaceCollection<E>
- Specified by:
spliterator
in interfaceIterable<E>
- Implementation Note:
- The
Spliterator
additionally reportsSpliterator.SUBSIZED
. - Returns:
- a
Spliterator
over the elements in this queue - Since:
- 1.8
-
removeIf
Description copied from interface:Collection
Removes all of the elements of this collection that satisfy the given predicate (optional operation). Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller.- Specified by:
removeIf
in interfaceCollection<E>
- Parameters:
filter
- a predicate which returnstrue
for elements to be removed- Returns:
true
if any elements were removed- Throws:
NullPointerException
- if the specified filter is null
-
removeAll
Description copied from class:AbstractCollection
Removes all of this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection.- Specified by:
removeAll
in interfaceCollection<E>
- Overrides:
removeAll
in classAbstractCollection<E>
- Parameters:
c
- collection containing elements to be removed from this collection- Returns:
true
if this collection changed as a result of the call- Throws:
NullPointerException
- if this collection contains one or more null elements and the specified collection does not support null elements (optional) or if the specified collection is null- See Also:
-
retainAll
Description copied from class:AbstractCollection
Retains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection.- Specified by:
retainAll
in interfaceCollection<E>
- Overrides:
retainAll
in classAbstractCollection<E>
- Parameters:
c
- collection containing elements to be retained in this collection- Returns:
true
if this collection changed as a result of the call- Throws:
NullPointerException
- if this collection contains one or more null elements and the specified collection does not permit null elements (optional) or if the specified collection is null- See Also:
-
forEach
Description copied from interface:Iterable
Performs the given action for each element of theIterable
until all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions thrown by the action are relayed to the caller.The behavior of this method is unspecified if the action performs side-effects that modify the underlying source of elements, unless an overriding class has specified a concurrent modification policy.
- Specified by:
forEach
in interfaceIterable<E>
- Parameters:
action
- The action to be performed for each element- Throws:
NullPointerException
- if the specified action is null
-