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 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 (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 (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 () 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 (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> 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

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

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

Specified by:

poll in interface Queue <E>

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

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

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

Specified by:

peek in interface Queue <E>

Returns:

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

size

public int size()

Description copied from class: AbstractCollection

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

Specified by:

size in interface Collection <E>

Specified by:

size in class AbstractCollection