API java : ArrayBlockingQueue

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 put an element to a full queue will result in the put 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 and its iterator implement all of the optional methods of the Collection and Iterator interfaces.

This class is a member of the Java Collections Framework.

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()           Atomically removes all of the elements from this queue.
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 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()           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 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 a single instance of the specified element from this queue, if it is present.
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 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
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

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

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.

remove

public boolean remove(Object o)

Removes a single instance of the specified element from this queue, if it is present.

Specified by:

remove in interface Collection<E>

Overrides:

remove in class AbstractCollection<E>

Parameters:

o - element to be removed from this collection, if present.

Returns:

true if the collection contained the specified element.

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.

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

Returns true if this collection contains the specified element. More formally, returns true if and only if this collection contains at least one element e such that (o==null ? e==null : o.equals(e)).

This implementation iterates over the elements in the collection, checking each element in turn for equality with the specified element.

Specified by:

contains in interface Collection<E>

Overrides:

contains in class AbstractCollection<E>

Parameters:

o - object to be checked for containment in this collection.

Returns:

true if this collection contains the specified element.

toArray

public Object[] toArray()

Description copied from class: AbstractCollection

Returns an array containing all of the elements in this collection. If the collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order. The returned array will be "safe" in that no references to it are maintained by the collection. (In other words, this method must allocate a new array even if the collection is backed by an Array). The caller is thus free to modify the returned array.

This implementation allocates the array to be returned, and iterates over the elements in the collection, storing each object reference in the next consecutive element of the array, starting with element 0.

Specified by:

toArray in interface Collection<E>

Overrides:

toArray in class AbstractCollection<E>

Returns:

an array containing all of the elements in this collection.

toArray

public <T> T[] toArray(T[] a)

Description copied from class: AbstractCollection

Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array. If the collection fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this collection.

If the collection fits in the specified array with room to spare (i.e., the array has more elements than the collection), the element in the array immediately following the end of the collection is set to null. This is useful in determining the length of the collection only if the caller knows that the collection does not contain any null elements.)

If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.

This implementation checks if the array is large enough to contain the collection; if not, it allocates a new array of the correct size and type (using reflection). Then, it iterates over the collection, storing each object reference in the next consecutive element of the array, starting with element 0. If the array is larger than the collection, a null is stored in the first location after the end of the collection.

Specified by:

toArray in interface Collection<E>

Overrides:

toArray in class AbstractCollection<E>

Parameters:

a - the array into which the elements of the collection are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.

Returns:

an array containing the elements of the collection.

toString

public String toString()

Description copied from class: AbstractCollection

Returns a string representation of this collection. The string representation consists of a list of the collection's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters ", " (comma and space). Elements are converted to strings as by String.valueOf(Object).

This implementation creates an empty string buffer, appends a left square bracket, and iterates over the collection appending the string representation of each element in turn. After appending each element except the last, the string ", " is appended. Finally a right bracket is appended. A string is obtained from the string buffer, and returned.

Overrides:

toString in class AbstractCollection<E>

Returns:

a string representation of this collection.

clear

public void clear()

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

Specified by:

clear in interface Collection<E>

Overrides:

clear in class AbstractQueue<E>

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.