PriorityBlockingQueue (Java 2 Platform SE 5.0) (original) (raw)

java.util.concurrent

Class PriorityBlockingQueue

java.lang.Object extended by java.util.AbstractCollection java.util.AbstractQueue java.util.concurrent.PriorityBlockingQueue

Type Parameters:

E - the type of elements held in this collection

All Implemented Interfaces:

Serializable, Iterable, Collection, BlockingQueue, Queue

public class PriorityBlockingQueue

extends AbstractQueue

implements BlockingQueue, Serializable

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 permitnull 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()).

This class is a member of the Java Collections Framework.

Since:

1.5

See Also:

Serialized Form

Constructor Summary
PriorityBlockingQueue() Creates a PriorityBlockingQueue with the default initial capacity (11) that orders its elements according to their natural ordering (using Comparable).
PriorityBlockingQueue(Collection<? extends E> c) Creates a PriorityBlockingQueue containing the elements in the specified collection.
PriorityBlockingQueue(int initialCapacity) Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to their natural ordering (using Comparable).
[PriorityBlockingQueue](../../../java/util/concurrent/PriorityBlockingQueue.html#PriorityBlockingQueue%28int, java.util.Comparator%29)(int initialCapacity,Comparator<? super E> comparator) Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to the specified comparator.

Method Summary
boolean	add(E o) Adds the specified element to this queue.
void	clear() Atomically removes all of the elements from this queue.
Comparator<? super E>	comparator() Returns the comparator used to order this collection, or null if this collection is sorted according to its elements natural ordering (using Comparable).
boolean	contains(Object o) Returns true if this collection contains the specified element.
int	drainTo(Collection<? super E> c) Removes all available elements from this queue and adds them into the given collection.
int	[drainTo](../../../java/util/concurrent/PriorityBlockingQueue.html#drainTo%28java.util.Collection, int%29)(Collection<? super E> c, int maxElements) Removes at most the given number of available elements from this queue and adds them into the given collection.
Iterator<E>	iterator() Returns an iterator over the elements in this queue.
boolean	offer(E o) Inserts the specified element into this priority queue.
boolean	[offer](../../../java/util/concurrent/PriorityBlockingQueue.html#offer%28E, long, java.util.concurrent.TimeUnit%29)(E o, long timeout,TimeUnit unit) Inserts the specified element into this priority queue.
E	peek() Retrieves, but does not remove, the head of this queue, returning null if this queue is empty.
E	poll() Retrieves and removes the head of this queue, or null if this queue is empty.
E	[poll](../../../java/util/concurrent/PriorityBlockingQueue.html#poll%28long, java.util.concurrent.TimeUnit%29)(long timeout,TimeUnit unit) Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time if no elements are present on this queue.
void	put(E o) Adds the specified element to this priority queue.
int	remainingCapacity() Always returns Integer.MAX_VALUE because a PriorityBlockingQueue is not capacity constrained.
boolean	remove(Object o) Removes a single instance of the specified element from this queue, if it is present.
int	size() Returns the number of elements in this collection.
E	take() Retrieves and removes the head of this queue, waiting if no elements are present on this queue.
Object[]	toArray() Returns an array containing all of the elements in this collection.
T[]	toArray(T[] a) Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.
String	toString() Returns a string representation of this collection.

Methods inherited from class java.util.AbstractQueue
addAll, element, remove

Methods inherited from class java.util.AbstractCollection
containsAll, isEmpty, removeAll, retainAll

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, [wait](../../../java/lang/Object.html#wait%28long, int%29)

Methods inherited from interface java.util.Queue
element, remove

Methods inherited from interface java.util.Collection
addAll, containsAll, equals, hashCode, isEmpty, removeAll, retainAll

Constructor Detail

PriorityBlockingQueue

public PriorityBlockingQueue()

Creates a PriorityBlockingQueue with the default initial capacity (11) that orders its elements according to their natural ordering (using Comparable).

PriorityBlockingQueue

public PriorityBlockingQueue(int initialCapacity)

Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to their natural ordering (using Comparable).

Parameters:

initialCapacity - the initial capacity for this priority queue.

Throws:

[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang") - if initialCapacity is less than 1

PriorityBlockingQueue

public PriorityBlockingQueue(int initialCapacity, Comparator<? super E> comparator)

Creates a PriorityBlockingQueue with the specified initial capacity that orders its elements according to the specified comparator.

Parameters:

initialCapacity - the initial capacity for this priority queue.

comparator - the comparator used to order this priority queue. If null then the order depends on the elements' natural ordering.

Throws:

[IllegalArgumentException](../../../java/lang/IllegalArgumentException.html "class in java.lang") - if initialCapacity is less than 1

PriorityBlockingQueue

public PriorityBlockingQueue(Collection<? extends E> c)

Creates a PriorityBlockingQueue containing the elements in the specified collection. The priority queue has an initial capacity of 110% of the size of the specified collection. If the specified collection is a SortedSet or a PriorityQueue, this priority queue will be sorted according to the same comparator, or according to its elements' natural order if the collection is sorted according to its elements' natural order. Otherwise, this priority queue is ordered according to its elements' natural order.

Parameters:

c - the collection whose elements are to be placed into this priority queue.

Throws:

[ClassCastException](../../../java/lang/ClassCastException.html "class in java.lang") - if elements of the specified collection cannot be compared to one another according to the priority queue's ordering.

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if c or any element within it is null

Method Detail

add

public boolean add(E o)

Adds the specified element to this queue.

Specified by:

[add](../../../java/util/Collection.html#add%28E%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Specified by:

[add](../../../java/util/concurrent/BlockingQueue.html#add%28E%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Overrides:

[add](../../../java/util/AbstractQueue.html#add%28E%29) in class [AbstractQueue](../../../java/util/AbstractQueue.html "class in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Parameters:

o - the element to add

Returns:

true (as per the general contract ofCollection.add).

Throws:

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified element is null.

[ClassCastException](../../../java/lang/ClassCastException.html "class in java.lang") - if the specified element cannot be compared with elements currently in the priority queue according to the priority queue's ordering.

comparator

public Comparator<? super E> comparator()

Returns the comparator used to order this collection, or null if this collection is sorted according to its elements natural ordering (using Comparable).

Returns:

the comparator used to order this collection, or null if this collection is sorted according to its elements natural ordering.

offer

public boolean offer(E o)

Inserts the specified element into this priority queue.

Specified by:

[offer](../../../java/util/concurrent/BlockingQueue.html#offer%28E%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Specified by:

[offer](../../../java/util/Queue.html#offer%28E%29) in interface [Queue](../../../java/util/Queue.html "interface in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Parameters:

o - the element to add

Returns:

true

Throws:

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified element is null.

put

public void put(E o)

Adds the specified element to this priority queue. As the queue is unbounded this method will never block.

Specified by:

[put](../../../java/util/concurrent/BlockingQueue.html#put%28E%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Parameters:

o - the element to add

Throws:

[ClassCastException](../../../java/lang/ClassCastException.html "class in java.lang") - if the element cannot be compared with elements currently in the priority queue according to the priority queue's ordering.

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified element is null.

offer

public boolean offer(E o, long timeout, TimeUnit unit)

Inserts the specified element into this priority queue. As the queue is unbounded this method will never block.

Specified by:

[offer](../../../java/util/concurrent/BlockingQueue.html#offer%28E, long, java.util.concurrent.TimeUnit%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Parameters:

o - the element to add

timeout - This parameter is ignored as the method never blocks

unit - This parameter is ignored as the method never blocks

Returns:

true

Throws:

[NullPointerException](../../../java/lang/NullPointerException.html "class in java.lang") - if the specified element is null.

take

public E take() throws InterruptedException

Description copied from interface: [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html#take%28%29)

Retrieves and removes the head of this queue, waiting if no elements are present on this queue.

Specified by:

[take](../../../java/util/concurrent/BlockingQueue.html#take%28%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Returns:

the head of this queue

Throws:

[InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang") - if interrupted while waiting.

poll

public E poll()

Description copied from interface: [Queue](../../../java/util/Queue.html#poll%28%29)

Retrieves and removes the head of this queue, or null if this queue is empty.

Specified by:

[poll](../../../java/util/Queue.html#poll%28%29) in interface [Queue](../../../java/util/Queue.html "interface in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Returns:

the head of this queue, or null if this queue is empty.

poll

public E poll(long timeout, TimeUnit unit) throws InterruptedException

Description copied from interface: [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html#poll%28long, java.util.concurrent.TimeUnit%29)

Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time if no elements are present on this queue.

Specified by:

[poll](../../../java/util/concurrent/BlockingQueue.html#poll%28long, java.util.concurrent.TimeUnit%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Parameters:

timeout - how long to wait before giving up, in units ofunit

unit - a TimeUnit determining how to interpret thetimeout parameter

Returns:

the head of this queue, or null if the specified waiting time elapses before an element is present.

Throws:

[InterruptedException](../../../java/lang/InterruptedException.html "class in java.lang") - if interrupted while waiting.

peek

public E peek()

Description copied from interface: [Queue](../../../java/util/Queue.html#peek%28%29)

Retrieves, but does not remove, the head of this queue, returning null if this queue is empty.

Specified by:

[peek](../../../java/util/Queue.html#peek%28%29) in interface [Queue](../../../java/util/Queue.html "interface in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Returns:

the head of this queue, or null if this queue is empty.

size

public int size()

Description copied from class: [AbstractCollection](../../../java/util/AbstractCollection.html#size%28%29)

Returns the number of elements in this collection. If the collection contains more than Integer.MAX_VALUE elements, returnsInteger.MAX_VALUE.

Specified by:

[size](../../../java/util/Collection.html#size%28%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Specified by:

[size](../../../java/util/AbstractCollection.html#size%28%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Returns:

the number of elements in this collection.

remainingCapacity

public int remainingCapacity()

Always returns Integer.MAX_VALUE because a PriorityBlockingQueue is not capacity constrained.

Specified by:

[remainingCapacity](../../../java/util/concurrent/BlockingQueue.html#remainingCapacity%28%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Returns:

Integer.MAX_VALUE

remove

public boolean remove(Object o)

Removes a single instance of the specified element from this queue, if it is present.

Specified by:

[remove](../../../java/util/Collection.html#remove%28java.lang.Object%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Overrides:

[remove](../../../java/util/AbstractCollection.html#remove%28java.lang.Object%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Parameters:

o - element to be removed from this collection, if present.

Returns:

true if the collection contained the specified element.

contains

public boolean contains(Object o)

Description copied from class: [AbstractCollection](../../../java/util/AbstractCollection.html#contains%28java.lang.Object%29)

Returns true if this collection contains the specified element. More formally, returns true if and only if this collection contains at least one element e such that(o==null ? e==null : o.equals(e)).

This implementation iterates over the elements in the collection, checking each element in turn for equality with the specified element.

Specified by:

[contains](../../../java/util/Collection.html#contains%28java.lang.Object%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Overrides:

[contains](../../../java/util/AbstractCollection.html#contains%28java.lang.Object%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Parameters:

o - object to be checked for containment in this collection.

Returns:

true if this collection contains the specified element.

toArray

public Object[] toArray()

Description copied from class: [AbstractCollection](../../../java/util/AbstractCollection.html#toArray%28%29)

Returns an array containing all of the elements in this collection. If the collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order. The returned array will be "safe" in that no references to it are maintained by the collection. (In other words, this method must allocate a new array even if the collection is backed by an Array). The caller is thus free to modify the returned array.

This implementation allocates the array to be returned, and iterates over the elements in the collection, storing each object reference in the next consecutive element of the array, starting with element 0.

Specified by:

[toArray](../../../java/util/Collection.html#toArray%28%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Overrides:

[toArray](../../../java/util/AbstractCollection.html#toArray%28%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Returns:

an array containing all of the elements in this collection.

toString

public String toString()

Description copied from class: [AbstractCollection](../../../java/util/AbstractCollection.html#toString%28%29)

Returns a string representation of this collection. The string representation consists of a list of the collection's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters", " (comma and space). Elements are converted to strings as by String.valueOf(Object).

This implementation creates an empty string buffer, appends a left square bracket, and iterates over the collection appending the string representation of each element in turn. After appending each element except the last, the string ", " is appended. Finally a right bracket is appended. A string is obtained from the string buffer, and returned.

Overrides:

[toString](../../../java/util/AbstractCollection.html#toString%28%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Returns:

a string representation of this collection.

drainTo

public int drainTo(Collection<? super E> c)

Description copied from interface: [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html#drainTo%28java.util.Collection%29)

Removes all available elements from this queue and adds them into 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 inIllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Specified by:

[drainTo](../../../java/util/concurrent/BlockingQueue.html#drainTo%28java.util.Collection%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Parameters:

c - the collection to transfer elements into

Returns:

the number of elements transferred.

drainTo

public int drainTo(Collection<? super E> c, int maxElements)

Description copied from interface: [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html#drainTo%28java.util.Collection, int%29)

Removes at most the given number of available elements from this queue and adds them into 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 inIllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Specified by:

[drainTo](../../../java/util/concurrent/BlockingQueue.html#drainTo%28java.util.Collection, int%29) in interface [BlockingQueue](../../../java/util/concurrent/BlockingQueue.html "interface in java.util.concurrent")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Parameters:

c - the collection to transfer elements into

maxElements - the maximum number of elements to transfer

Returns:

the number of elements transferred.

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](../../../java/util/Collection.html#clear%28%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Overrides:

[clear](../../../java/util/AbstractQueue.html#clear%28%29) in class [AbstractQueue](../../../java/util/AbstractQueue.html "class in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

toArray

public T[] toArray(T[] a)

Description copied from class: [AbstractCollection](../../../java/util/AbstractCollection.html#toArray%28T[]%29)

Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. If the collection 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 collection.

If the collection fits in the specified array with room to spare (i.e., the array has more elements than the collection), the element in the array immediately following the end of the collection is set tonull. This is useful in determining the length of the collection only if the caller knows that the collection does not contain any null elements.)

If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.

This implementation checks if the array is large enough to contain the collection; if not, it allocates a new array of the correct size and type (using reflection). Then, it iterates over the collection, storing each object reference in the next consecutive element of the array, starting with element 0. If the array is larger than the collection, a null is stored in the first location after the end of the collection.

Specified by:

[toArray](../../../java/util/Collection.html#toArray%28T[]%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Overrides:

[toArray](../../../java/util/AbstractCollection.html#toArray%28T[]%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Parameters:

a - the array into which the elements of the collection 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 the elements of the collection.

iterator

public Iterator<E> 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 a thread-safe "fast-fail" iterator that will throw ConcurrentModificationException upon detected interference.

Specified by:

[iterator](../../../java/lang/Iterable.html#iterator%28%29) in interface [Iterable](../../../java/lang/Iterable.html "interface in java.lang")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Specified by:

[iterator](../../../java/util/Collection.html#iterator%28%29) in interface [Collection](../../../java/util/Collection.html "interface in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Specified by:

[iterator](../../../java/util/AbstractCollection.html#iterator%28%29) in class [AbstractCollection](../../../java/util/AbstractCollection.html "class in java.util")<[E](../../../java/util/concurrent/PriorityBlockingQueue.html "type parameter in PriorityBlockingQueue")>

Returns:

an iterator over the elements in this queue.

Submit a bug or feature
For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.