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 put an element into a full queue will result in the operation blocking; attempts to take 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.

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
boolean add(E e)
Inserts the specified element at the tail of this queue if it is possible to do so immediately without exceeding the queue's capacity, returning true upon success and throwing an IllegalStateException if this queue is full.
void clear()
Atomically removes all of the elements from this queue.
boolean contains(Object o)
Returns true if this queue contains the specified element.
int drainTo(Collection<? super E> c, int maxElements)
Removes at most the given number of available elements from this queue and adds them to the given collection.
int drainTo(Collection<? super E> c)
Removes all available elements from this queue and adds them to the given collection.
Iterator<E> iterator()
Returns an iterator over the elements in this queue in proper sequence.
boolean offer(E e, long timeout, TimeUnit unit)
Inserts the specified element at the tail of this queue, waiting up to the specified wait time for space to become available if the queue is full.
boolean offer(E e)
Inserts the specified element at the tail of this queue if it is possible to do so immediately without exceeding the queue's capacity, returning true upon success and false 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 up to the specified wait time if necessary for an element to become available.
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 e)
Inserts the specified element at the tail of this queue, waiting for space to become available if the queue is full.
int remainingCapacity()
Returns the number of additional 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 necessary until an element becomes available.
<T> T[] toArray(T[] a)
Returns an array containing all of the elements in this queue, in proper sequence; the runtime type of the returned array is that of the specified array.
Object[] toArray()
Returns an array containing all of the elements in this queue, in proper sequence.
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)

Since: API Level 1

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)

Since: API Level 1

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)

Since: API Level 1

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 the specified collection or any of its elements are null

Public Methods

public boolean add (E e)

Since: API Level 1

Inserts the specified element at the tail of this queue if it is possible to do so immediately without exceeding the queue's capacity, returning true upon success and throwing an IllegalStateException if this queue is full.

Parameters
e the element to add
Returns
Throws
IllegalStateException if this queue is full
NullPointerException if the specified element is null

public void clear ()

Since: API Level 1

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

public boolean contains (Object o)

Since: API Level 1

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

Parameters
o object to be checked for containment in this queue
Returns
  • true if this queue contains the specified element

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

Since: API Level 1

Removes at most the given number of available elements from this queue and adds them to 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
Throws
UnsupportedOperationException
ClassCastException
NullPointerException
IllegalArgumentException

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

Since: API Level 1

Removes all available elements from this queue and adds them to 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
Throws
UnsupportedOperationException
ClassCastException
NullPointerException
IllegalArgumentException

public Iterator<E> iterator ()

Since: API Level 1

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 e, long timeout, TimeUnit unit)

Since: API Level 1

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

Parameters
e 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
NullPointerException

public boolean offer (E e)

Since: API Level 1

Inserts the specified element at the tail of this queue if it is possible to do so immediately without exceeding the queue's capacity, returning true upon success and false if this queue is full. This method is generally preferable to method add(E), which can fail to insert an element only by throwing an exception.

Parameters
e the element to add
Returns
  • true if the element was added to this queue, else false
Throws
NullPointerException if the specified element is null

public E peek ()

Since: API Level 1

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)

Since: API Level 1

Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.

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 available
Throws
InterruptedException

public E poll ()

Since: API Level 1

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 e)

Since: API Level 1

Inserts the specified element at the tail of this queue, waiting for space to become available if the queue is full.

Parameters
e the element to add
Throws
InterruptedException
NullPointerException

public int remainingCapacity ()

Since: API Level 1

Returns the number of additional 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 insert an element will succeed by inspecting remainingCapacity because it may be the case that another thread is about to insert or remove an element.

Returns
  • the remaining capacity

public boolean remove (Object o)

Since: API Level 1

Removes a single instance of the specified element from this queue, if it is present. More formally, removes an element e such that o.equals(e), if this queue contains one or more such elements. Returns true if this queue contained the specified element (or equivalently, if this queue changed as a result of the call).

Parameters
o element to be removed from this queue, if present
Returns
  • true if this queue changed as a result of the call

public int size ()

Since: API Level 1

Returns the number of elements in this queue.

Returns
  • the number of elements in this queue

public E take ()

Since: API Level 1

Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.

Returns
  • the head of this queue
Throws
InterruptedException

public T[] toArray (T[] a)

Since: API Level 1

Returns an array containing all of the elements in this queue, in proper sequence; the runtime type of the returned array is that of the specified array. If the queue 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 queue.

If this queue fits in the specified array with room to spare (i.e., the array has more elements than this queue), the element in the array immediately following the end of the queue is set to null.

Like the toArray() method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.

Suppose x is a queue known to contain only strings. The following code can be used to dump the queue into a newly allocated array of String: 

     String[] y = x.toArray(new String[0]);
Note that toArray(new Object[0]) is identical in function to toArray().

Parameters
a the array into which the elements of the queue 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 all of the elements in this queue
Throws
ArrayStoreException if the runtime type of the specified array is not a supertype of the runtime type of every element in this queue
NullPointerException if the specified array is null

public Object[] toArray ()

Since: API Level 1

Returns an array containing all of the elements in this queue, in proper sequence.

The returned array will be "safe" in that no references to it are maintained by this queue. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array.

This method acts as bridge between array-based and collection-based APIs.

Returns
  • an array containing all of the elements in this queue

public String toString ()

Since: API Level 1

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.