public class

PriorityBlockingQueue

extends AbstractQueue<E>
implements Serializable BlockingQueue<E>
java.lang.Object
   ↳ java.util.AbstractCollection<E>
     ↳ java.util.AbstractQueue<E>
       ↳ java.util.concurrent.PriorityBlockingQueue<E>

Class Overview

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()).

Summary

Public Constructors
PriorityBlockingQueue()
Creates a PriorityBlockingQueue with the default initial capacity (11) that orders its elements according to their natural ordering (using Comparable).
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.
PriorityBlockingQueue(Collection<? extends E> c)
Creates a PriorityBlockingQueue containing the elements in the specified collection.
Public Methods
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)
Tests whether this Collection contains the specified object.
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.
int drainTo(Collection<? super E> c)
Removes all 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, long timeout, TimeUnit unit)
Inserts the specified element into this priority queue.
boolean offer(E o)
Inserts the specified element into this priority queue.
E peek()
Gets but does not remove the element at the head of 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.
E poll()
Gets and removes the element at the head of the queue, or returns null if there is no element in the 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 one instance of the specified object from this Collection if one is contained (optional).
int size()
Returns a count of how many objects this Collection contains.
E take()
Retrieves and removes the head of this queue, waiting if no elements are present on this queue.
<T> T[] toArray(T[] a)
Returns an array containing all elements contained in this Collection.
Object[] toArray()
Returns a new array containing all elements contained in this Collection.
String toString()
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

Public Constructors

public PriorityBlockingQueue ()

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

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

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

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

Public Methods

public boolean add (E o)

Adds the specified element to this queue.

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.

public void clear ()

Atomically removes all of the elements from this delay queue. The queue will be empty after this call returns.

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.

public boolean contains (Object o)

Tests whether this Collection contains the specified object. This implementation iterates over this Collection and tests, whether any element is equal to the given object. If object != null then object.equals(e) is called for each element e returned by the iterator until the element is found. If object == null then each element e returned by the iterator is compared with the test e == null.

Parameters
o the object to search for.
Returns
  • true if object is an element of this Collection, false otherwise.

public 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. 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.

Parameters
c the collection to transfer elements into
maxElements the maximum number of elements to transfer
Returns
  • the number of elements transferred.

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

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.

Parameters
c the collection to transfer elements into
Returns
  • the number of elements transferred.

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.

Returns
  • an iterator over the elements in this queue.

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.

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.

public boolean offer (E o)

Inserts the specified element into this priority queue.

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.

public E peek ()

Gets but does not remove the element at the head of the queue.

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

public 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.

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

public E poll ()

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

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

public void put (E o)

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

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.

public int remainingCapacity ()

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

Returns
  • Integer.MAX_VALUE

public boolean remove (Object o)

Removes one instance of the specified object from this Collection if one is contained (optional). This implementation iterates over this Collection and tests for each element e returned by the iterator, whether e is equal to the given object. If object != null then this test is performed using object.equals(e), otherwise using object == null. If an element equal to the given object is found, then the remove method is called on the iterator and true is returned, false otherwise. If the iterator does not support removing elements, an UnsupportedOperationException is thrown.

Parameters
o the object to remove.
Returns
  • true if this Collection is modified, false otherwise.

public int size ()

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.

Returns
  • how many objects this Collection contains, or Integer.MAX_VALUE if there are more than Integer.MAX_VALUE elements in this Collection.

public E take ()

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

Returns
  • the head of this queue
Throws
InterruptedException

public T[] toArray (T[] a)

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. If the implementation has ordered elements it will return the element array in the same order as an iterator would return them. toArray(new Object[0]) behaves exactly the same way as toArray() does.

Parameters
a the array.
Returns
  • an array of the elements from this Collection.

public Object[] toArray ()

Returns a new array containing all elements contained in this Collection. If the implementation has ordered elements it will return the element array in the same order as an iterator would return them. The array returned does not reflect any changes of the Collection. A new array is created even if the underlying data structure is already an array.

Returns
  • an array of the elements from this Collection.

public String toString ()

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).

Returns
  • the string representation of this Collection.