Module java.base

Package 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 queue

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 changed. 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.

This class is a member of the Java Collections Framework.

Since:

1.5

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor	Description
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

Modifier and Type	Method	Description
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)	Removes all available elements from this queue and adds them to 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 to the given collection.
void	forEach(Consumer<? super E> action)	Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception.
Iterator<E>	iterator()	Returns an iterator over the elements in this queue in proper sequence.
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.
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.
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.
boolean	removeAll(Collection<?> c)	Removes all of this collection's elements that are also contained in the specified collection (optional operation).
boolean	removeIf(Predicate<? super E> filter)	Removes all of the elements of this collection that satisfy the given predicate.
boolean	retainAll(Collection<?> c)	Retains only the elements in this collection that are contained in the specified collection (optional operation).
int	size()	Returns the number of elements in this queue.
Spliterator<E>	spliterator()	Returns a Spliterator over the elements in this queue.
Object[]	toArray()	Returns an array containing all of the elements in this queue, in proper sequence.
<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.

Methods declared in class java.util.AbstractQueue

addAll, element, remove

Methods declared in class java.util.AbstractCollection

containsAll, isEmpty, toString

Methods declared in class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods declared in interface java.util.concurrent.BlockingQueue

poll, take

Methods declared in interface java.util.Collection

addAll, containsAll, equals, hashCode, isEmpty, parallelStream, stream, toArray

Methods declared in interface java.util.Queue

element, peek, poll, remove

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 < 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 < 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 the specified collection or any of its elements are null

Method Detail

add

public 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.

Specified by:

add in interface BlockingQueue<E>

Specified by:

add in interface Collection<E>

Specified by:

add in interface Queue<E>

Overrides:

add in class AbstractQueue<E>

Parameters:

e - the element to add

Returns:

true (as specified by Collection.add(E))

Throws:

IllegalStateException - if this queue is full

NullPointerException - if the specified element is null

offer

public 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. This method is generally preferable to method add(E), which can fail to insert an element only by throwing an exception.

Specified by:

offer in interface BlockingQueue<E>

Specified by:

offer in interface Queue<E>

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

put

public void put(E e)
         throws InterruptedException

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

Specified by:

put in interface BlockingQueue<E>

Parameters:

e - the element to add

Throws:

InterruptedException - if interrupted while waiting

NullPointerException - if the specified element is null

offer

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

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.

Specified by:

offer in interface BlockingQueue<E>

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 - 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>

Returns:

the number of elements in this queue

remainingCapacity

public int remainingCapacity()

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.

Specified by:

remainingCapacity in interface BlockingQueue<E>

Returns:

the remaining capacity

remove

public boolean remove(Object o)

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).

Removal of interior elements in circular array based queues is an intrinsically slow and disruptive operation, so should be undertaken only in exceptional circumstances, ideally only when the queue is known not to be accessible by other threads.

Specified by:

remove in interface BlockingQueue<E>

Specified by:

remove in interface Collection<E>

Overrides:

remove in class AbstractCollection<E>

Parameters:

o - element to be removed from this queue, if present

Returns:

true if this queue changed as a result of the call

contains

public boolean contains(Object o)

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).

Specified by:

contains in interface BlockingQueue<E>

Specified by:

contains in interface Collection<E>

Overrides:

contains in class AbstractCollection<E>

Parameters:

o - object to be checked for containment in this queue

Returns:

true if this queue contains the specified element

toArray

public Object[] toArray()

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.

Specified by:

toArray in interface Collection<E>

Overrides:

toArray in class AbstractCollection<