public class

ArrayBlockingQueue

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

Class Overview

A bounded blocking queue backed by an array. This queue orders elements FIFO (first-in-first-out). The head of the queue is that element that has been on the queue the longest time. The tail of the queue is that element that has been on the queue the shortest time. New elements are inserted at the tail of the queue, and the queue retrieval operations obtain elements at the head of the queue.

This is a classic "bounded buffer", in which a fixed-sized array holds elements inserted by producers and extracted by consumers. Once created, the capacity cannot be increased. Attempts to offer an element to a full queue will result in the offer operation blocking; attempts to retrieve an element from an empty queue will similarly block.

This class supports an optional fairness policy for ordering waiting producer and consumer threads. By default, this ordering is not guaranteed. However, a queue constructed with fairness set to true grants threads access in FIFO order. Fairness generally decreases throughput but reduces variability and avoids starvation.

This class implements all of the optional methods of the Collection and Iterator interfaces.

Summary

Public Constructors
ArrayBlockingQueue(int capacity)
Creates an ArrayBlockingQueue with the given (fixed) capacity and default access policy.
ArrayBlockingQueue(int capacity, boolean fair)
Creates an ArrayBlockingQueue with the given (fixed) capacity and the specified access policy.
ArrayBlockingQueue(int capacity, boolean fair, Collection<? extends E> c)
Creates an ArrayBlockingQueue with the given (fixed) capacity, the specified access policy and initially containing the elements of the given collection, added in traversal order of the collection's iterator.
Public Methods
void clear()
Removes all elements of the queue, leaving it empty.
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 in proper sequence.
boolean offer(E o, long timeout, TimeUnit unit)
Inserts the specified element at the tail of this queue, waiting if necessary up to the specified wait time for space to become available.
boolean offer(E o)
Inserts the specified element at the tail of this queue if possible, returning immediately if this queue is full.
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 the tail of this queue, waiting if necessary for space to become available.
int remainingCapacity()
Returns the number of elements that this queue can ideally (in the absence of memory or resource constraints) accept without blocking.
boolean remove(Object o)
Removes one instance of the specified object from this Collection if one is contained (optional).
int size()
Returns the number of elements in this queue.
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 ArrayBlockingQueue (int capacity)

Creates an ArrayBlockingQueue with the given (fixed) capacity and default access policy.

Parameters
capacity the capacity of this queue
Throws
IllegalArgumentException if capacity is less than 1

public ArrayBlockingQueue (int capacity, boolean fair)

Creates an ArrayBlockingQueue with the given (fixed) capacity and the specified access policy.

Parameters
capacity the capacity of this queue
fair if true then queue accesses for threads blocked on insertion or removal, are processed in FIFO order; if false the access order is unspecified.
Throws
IllegalArgumentException if capacity is less than 1

public ArrayBlockingQueue (int capacity, boolean fair, Collection<? extends E> c)

Creates an ArrayBlockingQueue with the given (fixed) capacity, the specified access policy and initially containing the elements of the given collection, added in traversal order of the collection's iterator.

Parameters
capacity the capacity of this queue
fair if true then queue accesses for threads blocked on insertion or removal, are processed in FIFO order; if false the access order is unspecified.
c the collection of elements to initially contain
Throws
IllegalArgumentException if capacity is less than c.size(), or less than 1.
NullPointerException if c or any element within it is null

Public Methods

public void clear ()

Removes all elements of the queue, leaving it empty.

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 in proper sequence. The returned Iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

Returns
  • an iterator over the elements in this queue in proper sequence.

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

Inserts the specified element at the tail of this queue, waiting if necessary up to the specified wait time for space to become available.

Parameters
o the element to add
timeout how long to wait before giving up, in units of unit
unit a TimeUnit determining how to interpret the timeout parameter
Returns
  • true if successful, or false if the specified waiting time elapses before space is available.
Throws
InterruptedException if interrupted while waiting.
NullPointerException if the specified element is null.

public boolean offer (E o)

Inserts the specified element at the tail of this queue if possible, returning immediately if this queue is full.

Parameters
o the element to add.
Returns
  • true if it was possible to add the element to this queue, else false
Throws
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 the tail of this queue, waiting if necessary for space to become available.

Parameters
o the element to add
Throws
InterruptedException if interrupted while waiting.
NullPointerException if the specified element is null.

public int remainingCapacity ()

Returns the number of elements that this queue can ideally (in the absence of memory or resource constraints) accept without blocking. This is always equal to the initial capacity of this queue less the current size of this queue.

Note that you cannot always tell if an attempt to add an element will succeed by inspecting remainingCapacity because it may be the case that a waiting consumer is ready to take an element out of an otherwise full queue.

Returns
  • the remaining capacity

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 the number of elements in this queue.

Returns
  • the number of elements in this queue.

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.