java.util.concurrent
Class ArrayBlockingQueue<E>

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

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.

Since:

1.5

See Also:

Serialized Form

Constructor Summary

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.

Method Summary

void	clear() Removes all elements of the queue.
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.
(package private) int	inc(int i) Circularly increment i.
Iterator<E>	iterator() Returns an iterator over the elements in this queue in proper sequence.
boolean	offer(E o) Inserts the specified element at the tail of this queue if possible, returning immediately if this queue is full.
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.
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 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 the first occurrence of the specified object from this Collection.
(package private) void	removeAt(int i) Utility for remove and iterator.remove: Delete item at position i.
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.
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

add, 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.concurrent.BlockingQueue

add

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

ArrayBlockingQueue

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

ArrayBlockingQueue

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

ArrayBlockingQueue

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

Method Detail

inc

final int inc(int i)

Circularly increment i.

removeAt

void removeAt(int i)

Utility for remove and iterator.remove: Delete item at position i. Call only when holding lock.

offer

public boolean offer(E o)

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

Specified by:

offer in interface BlockingQueue<E>

Specified by:

offer in interface Queue<E>

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

offer

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

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

Specified by:

offer in interface BlockingQueue<E>

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.

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.

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

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.

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.

put

public void put(E o)
         throws InterruptedException

Adds the specified element to the tail of this queue, waiting if necessary for space to become available.

Specified by:

put in interface BlockingQueue<E>

Parameters:

o - the element to add

Throws:

InterruptedException - if interrupted while waiting.

NullPointerException - if the specified element is null.

size

public int size()

Returns the number of elements in this queue.

Specified by:

size in interface Collection<E>

Specified by:

size in class AbstractCollection<E>

Returns:

the number of elements in this queue.

remainingCapacity

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.

Specified by:

remainingCapacity in interface BlockingQueue<E>

Returns:

the remaining capacity

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

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

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

clear

public void clear()

Description copied from class: AbstractQueue

Removes all elements of the queue.

Specified by:

clear in interface Collection<E>

Overrides:

clear in class AbstractQueue<E>

See Also:

Collection.isEmpty(), Collection.size()

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.

iterator

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.

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 in proper sequence.

See Also:

Iterator