java.util.concurrent
Class PriorityBlockingQueue<E>

java.lang.Object
  java.util.AbstractCollection<E>
      java.util.AbstractQueue<E>
          java.util.concurrent.PriorityBlockingQueue<E>

Type Parameters:

E - the type of elements held in this collection

All Implemented Interfaces:

Serializable, Iterable<E>, Collection<E>, BlockingQueue<E>, Queue<E>

public class PriorityBlockingQueue<E>
extends AbstractQueue<E>
implements BlockingQueue<E>, 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 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 implements 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()).

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(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 delay 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) Searches this Collection for the specified object.
int	drainTo(Collection<? super E> c) Removes all available elements from this queue and adds them into 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 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(E o, long timeout, TimeUnit unit) Inserts the specified element into this priority queue.
E	peek() Gets but not removes the element in the head of the queue, or throws exception if there is no element in the queue.
E	poll() Gets and removes the element in the head of the queue, or returns null if there is no element in the queue.
E	poll(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 the first occurrence of the specified object from this Collection.
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 a new array containing all elements contained in this Collection.
<T> T[]	toArray(T[] a) Returns an array containing all elements contained in this Collection.
String	toString() Returns the 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

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 - 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 - 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 - if elements of the specified collection cannot be compared to one another according to the priority queue's ordering.

NullPointerException - 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 in interface Collection<E>

Specified by:

add in interface BlockingQueue<E>

Overrides:

add in class AbstractQueue<E>

Parameters:

o - the element to add

Returns:

true (as per the general contract of Collection.add).

Throws:

NullPointerException - if the specified element is null.

ClassCastException - 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 in interface BlockingQueue<E>

Specified by:

offer in interface Queue<E>

Parameters:

o - the element to add

Returns:

true

Throws:

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.

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 in interface BlockingQueue<E>

Parameters:

o - the element to add

Throws:

ClassCastException - if the 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.

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 in interface BlockingQueue<E>

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:

ClassCastException - if the 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.

take

public E take()
       throws InterruptedException

Description copied from interface: BlockingQueue

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

Specified by:

take in interface BlockingQueue<E>

Returns:

the head of this queue

Throws:

InterruptedException - if interrupted while waiting.

poll

public E poll()

Description copied from interface: Queue

Gets and removes the element in the head of the queue, or returns null if there is no element in the queue.

Specified by:

poll in interface Queue<E>

Returns:

the element in the head of the queue or null if there is no element in the queue.

poll

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

Description copied from interface: BlockingQueue

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 in interface BlockingQueue<E>

Parameters:

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

unit - a TimeUnit determining how to interpret the timeout parameter

Returns:

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

Throws:

InterruptedException - if interrupted while waiting.

peek

public E peek()

Description copied from interface: Queue

Gets but not removes the element in the head of the queue, or throws exception if there is no element in the queue.

Specified by:

peek in interface Queue<E>

Returns:

the element in the head of the queue or null if there is no element in the queue.

size

public int size()

Description copied from class: AbstractCollection

Returns the number of elements in this Collection.

Specified by:

size in interface Collection<E>

Specified by:

size in class AbstractCollection<E>

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 in interface BlockingQueue<E>

Returns:

Integer.MAX_VALUE

remove

public boolean remove(Object o)

Description copied from class: AbstractCollection

Removes the first occurrence of the specified object from this Collection. This operation traverses over the collection, looking for the specified object. Once the object is found, the object will be removed from the collection using the iterator's remove method. This collection will throw an UnsupportedOperationException if the iterator returned does not implement remove method, and the specified object is in this collection.

Specified by:

remove in interface Collection<E>

Overrides:

remove in class AbstractCollection<E>

Parameters:

o - the object to remove

Returns:

true if this Collection is modified, false otherwise

contains

public boolean contains(Object o)

Description copied from class: AbstractCollection

Searches this Collection for the specified object.

Specified by:

contains in interface Collection<E>

Overrides:

contains in class AbstractCollection<E>

Parameters:

o - the object to search for

Returns:

true if object is an element of this Collection, false otherwise

toArray

public Object[] toArray()

Description copied from class: AbstractCollection

Returns a new array containing all elements contained in this Collection. All the elements in the array will not be referenced by the collection. The elements in the returned array will be sorted to the same order as those returned by the iterator of this collection itself if the collection guarantees the order.

Specified by:

toArray in interface Collection<E>

Overrides:

toArray in class AbstractCollection<E>

Returns:

an array of the elements from this Collection

toString

public String toString()

Description copied from class: AbstractCollection

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).

Overrides:

toString in class AbstractCollection<E>

Returns:

the string representation of this Collection

drainTo

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

Description copied from interface: BlockingQueue

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 in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Specified by:

drainTo in interface BlockingQueue<E>

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

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 in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Specified by:

drainTo in interface BlockingQueue<E>

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 delay queue. The queue will be empty after this call returns.

Specified by:

clear in interface Collection<E>

Overrides:

clear in class AbstractQueue<E>

See Also:

Collection.isEmpty(), Collection.size()

toArray

public <T> T[] toArray(T[] a)

Description copied from class: AbstractCollection

Returns an array containing all elements contained in this Collection. If the specified array is large enough to hold the elements, the specified array is used, otherwise an array of the same type is created. If the specified array is used and is larger than this Collection, the array element following the collection elements is set to null.

Specified by:

toArray in interface Collection<E>

Overrides:

toArray in class AbstractCollection<E>

Parameters:

a - the array

Returns:

an array of the elements from this 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 in interface Iterable<E>

Specified by:

iterator in interface Collection<E>

Specified by:

iterator in class AbstractCollection<E>

Returns:

an iterator over the elements in this queue.

See Also:

Iterator