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 into to a full queue will result in the put operation blocking; attempts to take 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
boolean	add ( 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           Returns true if this queue collection contains the specified element.
int	drainTo ( Collection <? super E           Removes all available elements from this queue and adds them to into the given collection.
int	drainTo ( Collection <? super E           Removes at most the given number of available elements from this queue and adds them to into the given collection.
Iterator < E >	iterator ()           Returns an iterator over the elements in this queue in proper sequence.
boolean	offer ( E           Inserts the specified element at the tail of this queue if it is possible to do so possible, returning immediately without exceeding the queue's capacity, returning true upon success and false if this queue is full.
boolean	offer ( E  e,  o, long timeout, TimeUnit           Inserts the specified element at the tail of this queue, waiting if necessary up to the specified wait time for space to become available if the queue is full. available.
E	peek ()           Retrieves, but does not remove, the head of this queue, or returns returning null if this queue is empty.
E	poll ()           Retrieves and removes the head of this queue, or returns null if this queue is empty.
E	poll (long timeout, TimeUnit           Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time if necessary for an element to become available. no elements are present on this queue.
void	put ( E           Inserts           Adds the specified element at to the tail of this queue, waiting if necessary for space to become available if the queue is full. available.
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. no elements are present on this queue.
Object	toArray ()           Returns an array containing all of the elements in this queue, in proper sequence. collection.
<T> T[]	toArray (T[] a)           Returns an array containing all of the elements in this queue, in proper sequence; 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 the specified collection or any of its elements are null - if c or any element within it is null

add offer

public boolean add offer (E e)  o) 

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

Specified by:

add offer in interface Collection < E >

Specified by:

add in interface BlockingQueue < E >

Specified by:

add offer in interface Queue < E >

Overrides:

add in class AbstractQueue < E >

Parameters:

e o - the element to add add.

Returns:

true (as specified by Collection.add(E) ) if it was possible to add the element to this queue, else false

Throws:

IllegalStateException - if this queue is full

NullPointerException - if the specified element is null

offer

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

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. 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 offer in interface BlockingQueue < E >

Specified by:

offer in interface Queue < E >

Parameters:

e - the element to add 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 the element was added to this queue, else 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 .

put poll

public void 
public Eput poll ( 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. Description copied from interface: Queue

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

Specified by:

put poll in interface BlockingQueue Queue < E >

Parameters: Returns:

e - the element to add

Throws:

InterruptedException - if interrupted while waiting

NullPointerException - if the specified element is null the head of this queue, or null if this queue is empty.

offer poll

public boolean 
public Eoffer poll ( E(long timeout,
 TimeUnit e,
 long timeout,
 TimeUnit unit)
 throws InterruptedException 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. 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:

offer poll 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:

the head of this queue, or true null if successful, or false if the specified waiting time elapses before space an element is available present.

Throws:

InterruptedException - if interrupted while waiting

NullPointerException - if the specified element is null - if interrupted while waiting.

poll remove

public E
public boolean poll remove () ( Object o) 

Description copied from interface: Queue

Retrieves and removes the head of this queue, or returns null if this queue is empty. Removes a single instance of the specified element from this queue, if it is present.

Specified by:

poll remove in interface Queue Collection < E >

Overrides:

remove in class AbstractCollection < E >

Parameters:

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

Returns:

the head of this queue, or null true if this queue is empty if the collection contained the specified element.

take peek

public Etake peek ()
 throws InterruptedException() 

Description copied from interface: BlockingQueue Queue

Retrieves and removes the head of this queue, waiting if necessary until an element becomes available. Retrieves, but does not remove, the head of this queue, returning null if this queue is empty.

Specified by:

take peek in interface BlockingQueue Queue < E >

Returns:

the head of this queue

Throws:

InterruptedException - if interrupted while waiting the head of this queue, or null if this queue is empty.

poll take

public Epoll take (long timeout,
 TimeUnit()
 throws InterruptedException unit)
 throws InterruptedException

Description copied from interface: BlockingQueue BlockingQueue

Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available. no elements are present on this queue.

Specified by:

poll take 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 available the head of this queue

Throws:

InterruptedException - if interrupted while waiting waiting.

peek put

public E
public void peek put () ( E o)
 throws InterruptedException

Description copied from interface: Queue

Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty. Adds the specified element to the tail of this queue, waiting if necessary for space to become available.

Specified by:

peek put in interface Queue BlockingQueue < E >

Returns: Parameters:

the head of this queue, or o - the element to add

Throws:

InterruptedException - if interrupted while waiting.

NullPointerException - if the specified element is null if this queue is empty .

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

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).

Specified by:

remove in interface Collection < E >

Specified by:

remove in interface BlockingQueue < 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)

Description copied from class: AbstractCollection

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

Specified by:

contains in interface BlockingQueue < E >

Overrides:

contains in class AbstractCollection < E >

Parameters:

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

Returns:

true if this queue collection contains the specified element element.

toArray

public Object[] toArray()

Description copied from class: AbstractCollection

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

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

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

toArray

public <T> T[] toArray(T[] a)

Description copied from class: AbstractCollection

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

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

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. 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.

Suppose 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 x null 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() . 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 queue collection are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose 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 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) 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 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 to 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 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

Throws:

UnsupportedOperationException - if addition of elements is not supported by the specified collection

ClassCastException - if the class of an element of this queue prevents it from being added to the specified collection

NullPointerException - if the specified collection is null

IllegalArgumentException - if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection 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 to into the given collection. A failure encountered while attempting to add elements to collection 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

Throws:

UnsupportedOperationException - if addition of elements is not supported by the specified collection

ClassCastException - if the class of an element of this queue prevents it from being added to the specified collection

NullPointerException - if the specified collection is null

IllegalArgumentException - if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection 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 sequence.