Android
java.util.concurrent
public class

java.util.concurrent.PriorityBlockingQueue<E>

java.lang.Object
java.util.AbstractCollection<E> Collection<E>
java.util.AbstractQueue<E> Queue<E>
java.util.concurrent.PriorityBlockingQueue<E> Serializable BlockingQueue<E>

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)
Searches this Collection for 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.
          peek()
Gets but not removes the element in the head of the queue, or throws exception if there is no element in the queue.
          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.
          poll()
Gets and removes the element in 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 the first occurrence of the specified object from this Collection.
          int  size()
Returns the number of elements in this Collection.
          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.
Methods inherited from class java.util.AbstractQueue
Methods inherited from class java.util.AbstractCollection
Methods inherited from class java.lang.Object
Methods inherited from interface java.lang.Iterable
Methods inherited from interface java.util.Collection
Methods inherited from interface java.util.Queue
Methods inherited from interface java.util.concurrent.BlockingQueue

Details

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)

Searches this Collection for the specified object.

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.

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.

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 not removes the element in the head of the queue, or throws exception 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.

public E poll()

Gets and removes the element in the head of the queue, or returns 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 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.

Parameters

o the object to remove

Returns

  • true if this Collection is modified, false otherwise

public int size()

Returns the number of elements in this Collection.

Returns

  • the number of elements in this Collection

public E take()

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

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.

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. 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.

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
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