Added in API level 1

Summary: Ctors | Methods | Inherited Methods

ArrayBlockingQueue

public class ArrayBlockingQueue
extends AbstractQueue<E> implements BlockingQueue<E>, Serializable

java.lang.Object
↳	java.util.AbstractCollection<E>
	↳	java.util.AbstractQueue<E>
		↳	java.util.concurrent.ArrayBlockingQueue<E>

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.

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.
`void`	`forEach(Consumer<? super E> action)`
`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.
`E`	`peek()` Retrieves, but does not remove, the head of this queue, or returns `null` if this queue is empty.
`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()` Retrieves and removes the head of this queue, or returns `null` if this queue is empty.
`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.
`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 a string representation of this collection.

Inherited methods

From class


        
          java.util.AbstractQueue

`boolean`	`add(E e)` Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions, returning `true` upon success and throwing an `IllegalStateException` if no space is currently available.
`boolean`	`addAll(Collection<? extends E> c)` Adds all of the elements in the specified collection to this queue.
`void`	`clear()` Removes all of the elements from this queue.
`E`	`element()` Retrieves, but does not remove, the head of this queue.
`E`	`remove()` Retrieves and removes the head of this queue.

From class


        
          java.util.AbstractCollection

`boolean`	`add(E e)` Ensures that this collection contains the specified element (optional operation).
`boolean`	`addAll(Collection<? extends E> c)` Adds all of the elements in the specified collection to this collection (optional operation).
`void`	`clear()` Removes all of the elements from this collection (optional operation).
`boolean`	`contains(Object o)` Returns `true` if this collection contains the specified element.
`boolean`	`containsAll(Collection<?> c)` Returns `true` if this collection contains all of the elements in the specified collection.
`boolean`	`isEmpty()` Returns `true` if this collection contains no elements.
`abstract Iterator<E>`	`iterator()` Returns an iterator over the elements contained in this collection.
`boolean`	`remove(Object o)` Removes a single instance of the specified element from this collection, if it is present (optional operation).
`boolean`	`removeAll(Collection<?> c)` Removes all of this collection's elements that are also contained in the specified collection (optional operation).
`boolean`	`retainAll(Collection<?> c)` Retains only the elements in this collection that are contained in the specified collection (optional operation).
`abstract int`	`size()` Returns the number of 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.
`Object[]`	`toArray()` Returns an array containing all of the elements in this collection.
`String`	`toString()` Returns a string representation of this collection.

From class


        
          java.lang.Object

`Object`	`clone()` Creates and returns a copy of this object.
`boolean`	`equals(Object obj)` Indicates whether some other object is "equal to" this one.
`void`	`finalize()` Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`final Class<?>`	`getClass()` Returns the runtime class of this `Object`.
`int`	`hashCode()` Returns a hash code value for the object.
`final void`	`notify()` Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()` Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()` Returns a string representation of the object.
`final void`	`wait(long timeoutMillis, int nanos)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait()` Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

From interface


        
          java.util.Queue

`abstract boolean`	`add(E e)` Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions, returning `true` upon success and throwing an `IllegalStateException` if no space is currently available.
`abstract E`	`element()` Retrieves, but does not remove, the head of this queue.
`abstract boolean`	`offer(E e)` Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions.
`abstract E`	`peek()` Retrieves, but does not remove, the head of this queue, or returns `null` if this queue is empty.
`abstract E`	`poll()` Retrieves and removes the head of this queue, or returns `null` if this queue is empty.
`abstract E`	`remove()` Retrieves and removes the head of this queue.

From interface


        
          java.util.Collection

`abstract boolean`	`add(E e)` Ensures that this collection contains the specified element (optional operation).
`abstract boolean`	`addAll(Collection<? extends E> c)` Adds all of the elements in the specified collection to this collection (optional operation).
`abstract void`	`clear()` Removes all of the elements from this collection (optional operation).
`abstract boolean`	`contains(Object o)` Returns `true` if this collection contains the specified element.
`abstract boolean`	`containsAll(Collection<?> c)` Returns `true` if this collection contains all of the elements in the specified collection.
`abstract boolean`	`equals(Object o)` Compares the specified object with this collection for equality.
`abstract int`	`hashCode()` Returns the hash code value for this collection.
`abstract boolean`	`isEmpty()` Returns `true` if this collection contains no elements.
`abstract Iterator<E>`	`iterator()` Returns an iterator over the elements in this collection.
`default Stream<E>`	`parallelStream()` Returns a possibly parallel `Stream` with this collection as its source.
`abstract boolean`	`remove(Object o)` Removes a single instance of the specified element from this collection, if it is present (optional operation).
`abstract boolean`	`removeAll(Collection<?> c)` Removes all of this collection's elements that are also contained in the specified collection (optional operation).
`default boolean`	`removeIf(Predicate<? super E> filter)` Removes all of the elements of this collection that satisfy the given predicate.
`abstract boolean`	`retainAll(Collection<?> c)` Retains only the elements in this collection that are contained in the specified collection (optional operation).
`abstract int`	`size()` Returns the number of elements in this collection.
`default Spliterator<E>`	`spliterator()` Creates a `Spliterator` over the elements in this collection.
`default Stream<E>`	`stream()` Returns a sequential `Stream` with this collection as its source.
`abstract <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.
`abstract Object[]`	`toArray()` Returns an array containing all of the elements in this collection.
`default <T> T[]`	`toArray(IntFunction<T[]> generator)` Returns an array containing all of the elements in this collection, using the provided `generator` function to allocate the returned array.

From interface


        
          java.util.concurrent.BlockingQueue

`abstract boolean`	`add(E e)` Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions, returning `true` upon success and throwing an `IllegalStateException` if no space is currently available.
`abstract boolean`	`contains(Object o)` Returns `true` if this queue contains the specified element.
`abstract int`	`drainTo(Collection<? super E> c)` Removes all available elements from this queue and adds them to the given collection.
`abstract 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.
`abstract boolean`	`offer(E e)` Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions, returning `true` upon success and `false` if no space is currently available.
`abstract boolean`	`offer(E e, long timeout, TimeUnit unit)` Inserts the specified element into this queue, waiting up to the specified wait time if necessary for space to become available.
`abstract 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.
`abstract void`	`put(E e)` Inserts the specified element into this queue, waiting if necessary for space to become available.
`abstract int`	`remainingCapacity()` Returns the number of additional elements that this queue can ideally (in the absence of memory or resource constraints) accept without blocking, or `Integer.MAX_VALUE` if there is no intrinsic limit.
`abstract boolean`	`remove(Object o)` Removes a single instance of the specified element from this queue, if it is present.
`abstract E`	`take()` Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.

From interface


        
          java.lang.Iterable

`default void`	`forEach(Consumer<? super T> action)` Performs the given action for each element of the `Iterable` until all elements have been processed or the action throws an exception.
`abstract Iterator<E>`	`iterator()` Returns an iterator over elements of type `T`.
`default Spliterator<E>`	`spliterator()` Creates a `Spliterator` over the elements described by this `Iterable`.

Public constructors

ArrayBlockingQueue

Added in API level 1

public ArrayBlockingQueue (int capacity)

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

Parameters
`capacity`	`int`: the capacity of this queue

Throws
`IllegalArgumentException`	if `capacity < 1`

ArrayBlockingQueue

Added in API level 1

public ArrayBlockingQueue (int capacity, 
                boolean fair)

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

Parameters
`capacity`	`int`: the capacity of this queue
`fair`	`boolean`: 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

Added in API level 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`	`int`: the capacity of this queue
`fair`	`boolean`: 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`	`Collection`: 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

add

Added in API level 1

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.

Parameters
`e`	`E`: the element to add

Returns
`boolean`	`true` (as specified by `Collection#add`)

Throws
`IllegalStateException`	if this queue is full
`NullPointerException`	if the specified element is null

clear

Added in API level 1

public void clear ()

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

contains

Added in API level 1

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).

Parameters
`o`	`Object`: object to be checked for containment in this queue

Returns
`boolean`	`true` if this queue contains the specified element

drainTo

Added in API level 1

public 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. 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`	`Collection`: the collection to transfer elements into
`maxElements`	`int`: the maximum number of elements to transfer

Returns
`int`	the number of elements transferred

Throws
`UnsupportedOperationException`
`ClassCastException`
`NullPointerException`
`IllegalArgumentException`

drainTo

Added in API level 1

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

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`	`Collection`: the collection to transfer elements into

Returns
`int`	the number of elements transferred

Throws
`UnsupportedOperationException`
`ClassCastException`
`NullPointerException`
`IllegalArgumentException`

forEach

Added in API level 24

public void forEach (Consumer<? super E> action)

Parameters
`action`	`Consumer`

Throws
`NullPointerException`

iterator

Added in API level 1

public Iterator<E> iterator ()

Returns an iterator over the elements in this queue in proper sequence. The elements will be returned in order from first (head) to last (tail).

The returned iterator is weakly consistent.

Returns
`Iterator<E>`	an iterator over the elements in this queue in proper sequence

offer

Added in API level 1

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.

Parameters
`e`	`E`: the element to add

Returns
`boolean`	`true` if the element was added to this queue, else `false`

Throws
`NullPointerException`	if the specified element is null

offer

Added in API level 1

public 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.

Parameters
`e`	`E`: the element to add
`timeout`	`long`: how long to wait before giving up, in units of `unit`
`unit`	`TimeUnit`: a `TimeUnit` determining how to interpret the `timeout` parameter

Returns
`boolean`	`true` if successful, or `false` if the specified waiting time elapses before space is available

Throws
`InterruptedException`
`NullPointerException`

peek

Added in API level 1

public E peek ()

Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.

Returns
`E`	the head of this queue, or `null` if this queue is empty

poll

Added in API level 1

public 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.

Parameters
`timeout`	`long`: how long to wait before giving up, in units of `unit`
`unit`	`TimeUnit`: a `TimeUnit` determining how to interpret the `timeout` parameter

Returns
`E`	the head of this queue, or `null` if the specified waiting time elapses before an element is available

Throws
`InterruptedException`

poll

Added in API level 1

public E poll ()

Retrieves and removes the head of this queue, or returns null if this queue is empty.

Returns
`E`	the head of this queue, or `null` if this queue is empty

put

Added in API level 1

public 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.

Parameters
`e`	`E`: the element to add

Throws
`InterruptedException`
`NullPointerException`

remainingCapacity

Added in API level 1

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.

Returns
`int`	the remaining capacity

remove

Added in API level 1

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.

Parameters
`o`	`Object`: element to be removed from this queue, if present

Returns
`boolean`	`true` if this queue changed as a result of the call

removeAll

Added in API level 1

public boolean removeAll (Collection<?> c)

Removes all of this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection.

Parameters
`c`	`Collection`: collection containing elements to be removed from this collection

Returns
`boolean`	`true` if this collection changed as a result of the call

Throws
`NullPointerException`

removeIf

Added in API level 24

public boolean removeIf (Predicate<? super E> filter)

Removes all of the elements of this collection that satisfy the given predicate. Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller.

Parameters
`filter`	`Predicate`: a predicate which returns `true` for elements to be removed

Returns
`boolean`	`true` if any elements were removed

Throws
`NullPointerException`

retainAll

Added in API level 1

public boolean retainAll (Collection<?> c)

Retains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection.

Parameters
`c`	`Collection`: collection containing elements to be retained in this collection

Returns
`boolean`	`true` if this collection changed as a result of the call

Throws
`NullPointerException`

size

Added in API level 1

public int size ()

Returns the number of elements in this queue.

Returns
`int`	the number of elements in this queue

spliterator

Added in API level 24

public Spliterator<E> spliterator ()

Returns a Spliterator over the elements in this queue.

The returned spliterator is weakly consistent.

The Spliterator reports Spliterator#CONCURRENT, Spliterator#ORDERED, and Spliterator#NONNULL.

Implementation Note:

The Spliterator implements trySplit to permit limited parallelism.

Returns
`Spliterator<E>`	a `Spliterator` over the elements in this queue

take

Added in API level 1

public E take ()

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

Returns
`E`	the head of this queue

Throws
`InterruptedException`

toArray

Added in API level 1

public 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. 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`	`T`: 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
`T[]`	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

toArray

Added in API level 1

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.

Returns
`Object[]`	an array containing all of the elements in this queue

toString

Added in API level 1

public String toString ()

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).

Returns
`String`	a string representation of this collection