- java.lang.Object
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- java.util.AbstractCollection<E>
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- java.util.AbstractQueue<E>
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- java.util.concurrent.ArrayBlockingQueue<E>
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- 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
putan element into a full queue will result in the operation blocking; attempts totakean 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
truegrants 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
CollectionandIteratorinterfaces.This class is a member of the Java Collections Framework.
- Since:
- 1.5
- See Also:
- Serialized Form
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Constructor Summary
Constructors Constructor Description ArrayBlockingQueue(int capacity)Creates anArrayBlockingQueuewith the given (fixed) capacity and default access policy.ArrayBlockingQueue(int capacity, boolean fair)Creates anArrayBlockingQueuewith the given (fixed) capacity and the specified access policy.ArrayBlockingQueue(int capacity, boolean fair, Collection<? extends E> c)Creates anArrayBlockingQueuewith 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.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description booleanadd(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, returningtrueupon success and throwing anIllegalStateExceptionif this queue is full.voidclear()Atomically removes all of the elements from this queue.booleancontains(Object o)Returnstrueif this queue contains the specified element.intdrainTo(Collection<? super E> c)Removes all available elements from this queue and adds them to the given collection.intdrainTo(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.voidforEach(Consumer<? super E> action)Performs the given action for each element of theIterableuntil 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.booleanoffer(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, returningtrueupon success andfalseif this queue is full.booleanoffer(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.voidput(E e)Inserts the specified element at the tail of this queue, waiting for space to become available if the queue is full.intremainingCapacity()Returns the number of additional elements that this queue can ideally (in the absence of memory or resource constraints) accept without blocking.booleanremove(Object o)Removes a single instance of the specified element from this queue, if it is present.booleanremoveAll(Collection<?> c)Removes all of this collection's elements that are also contained in the specified collection (optional operation).booleanremoveIf(Predicate<? super E> filter)Removes all of the elements of this collection that satisfy the given predicate.booleanretainAll(Collection<?> c)Retains only the elements in this collection that are contained in the specified collection (optional operation).intsize()Returns the number of elements in this queue.Spliterator<E>spliterator()Returns aSpliteratorover 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
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Methods declared in class java.util.AbstractCollection
containsAll, isEmpty, toString
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Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
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Methods declared in interface java.util.concurrent.BlockingQueue
poll, take
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Methods declared in interface java.util.Collection
addAll, containsAll, equals, hashCode, isEmpty, parallelStream, stream, toArray
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Constructor Detail
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ArrayBlockingQueue
public ArrayBlockingQueue(int capacity)
Creates anArrayBlockingQueuewith the given (fixed) capacity and default access policy.- Parameters:
capacity- the capacity of this queue- Throws:
IllegalArgumentException- ifcapacity < 1
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ArrayBlockingQueue
public ArrayBlockingQueue(int capacity, boolean fair)Creates anArrayBlockingQueuewith the given (fixed) capacity and the specified access policy.- Parameters:
capacity- the capacity of this queuefair- iftruethen queue accesses for threads blocked on insertion or removal, are processed in FIFO order; iffalsethe access order is unspecified.- Throws:
IllegalArgumentException- ifcapacity < 1
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ArrayBlockingQueue
public ArrayBlockingQueue(int capacity, boolean fair, Collection<? extends E> c)Creates anArrayBlockingQueuewith 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 queuefair- iftruethen queue accesses for threads blocked on insertion or removal, are processed in FIFO order; iffalsethe access order is unspecified.c- the collection of elements to initially contain- Throws:
IllegalArgumentException- ifcapacityis less thanc.size(), or less than 1.NullPointerException- if the specified collection or any of its elements are null
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Method Detail
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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, returningtrueupon success and throwing anIllegalStateExceptionif this queue is full.- Specified by:
addin interfaceBlockingQueue<E>- Specified by:
addin interfaceCollection<E>- Specified by:
addin interfaceQueue<E>- Overrides:
addin classAbstractQueue<E>- Parameters:
e- the element to add- Returns:
true(as specified byCollection.add(E))- Throws:
IllegalStateException- if this queue is fullNullPointerException- if the specified element is null
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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, returningtrueupon success andfalseif this queue is full. This method is generally preferable to methodadd(E), which can fail to insert an element only by throwing an exception.- Specified by:
offerin interfaceBlockingQueue<E>- Specified by:
offerin interfaceQueue<E>- Parameters:
e- the element to add- Returns:
trueif the element was added to this queue, elsefalse- Throws:
NullPointerException- if the specified element is null
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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:
putin interfaceBlockingQueue<E>- Parameters:
e- the element to add- Throws:
InterruptedException- if interrupted while waitingNullPointerException- if the specified element is null
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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:
offerin interfaceBlockingQueue<E>- Parameters:
e- the element to addtimeout- how long to wait before giving up, in units ofunitunit- aTimeUnitdetermining how to interpret thetimeoutparameter- Returns:
trueif successful, orfalseif the specified waiting time elapses before space is available- Throws:
InterruptedException- if interrupted while waitingNullPointerException- if the specified element is null
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size
public int size()
Returns the number of elements in this queue.- Specified by:
sizein interfaceCollection<E>- Returns:
- the number of elements in this queue
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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 currentsizeof this queue.Note that you cannot always tell if an attempt to insert an element will succeed by inspecting
remainingCapacitybecause it may be the case that another thread is about to insert or remove an element.- Specified by:
remainingCapacityin interfaceBlockingQueue<E>- Returns:
- the remaining capacity
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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 elementesuch thato.equals(e), if this queue contains one or more such elements. Returnstrueif 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:
removein interfaceBlockingQueue<E>- Specified by:
removein interfaceCollection<E>- Overrides:
removein classAbstractCollection<E>- Parameters:
o- element to be removed from this queue, if present- Returns:
trueif this queue changed as a result of the call
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contains
public boolean contains(Object o)
Returnstrueif this queue contains the specified element. More formally, returnstrueif and only if this queue contains at least one elementesuch thato.equals(e).- Specified by:
containsin interfaceBlockingQueue<E>- Specified by:
containsin interfaceCollection<E>- Overrides:
containsin classAbstractCollection<E>- Parameters:
o- object to be checked for containment in this queue- Returns:
trueif this queue contains the specified element
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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:
toArrayin interfaceCollection<E>- Overrides:
toArrayin classAbstractCollection<E>- Returns:
- an array containing all of the elements in this queue
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toArray
public <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. 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
xis a queue known to contain only strings. The following code can be used to dump the queue into a newly allocated array ofString:
Note thatString[] y = x.toArray(new String[0]);toArray(new Object[0])is identical in function totoArray().- Specified by:
toArrayin interfaceCollection<E>- Overrides:
toArrayin classAbstractCollection<E>- Type Parameters:
T- the component type of the array to contain the collection- 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 queueNullPointerException- if the specified array is null
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clear
public void clear()
Atomically removes all of the elements from this queue. The queue will be empty after this call returns.- Specified by:
clearin interfaceCollection<E>- Overrides:
clearin classAbstractQueue<E>
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drainTo
public int drainTo(Collection<? super E> c)
Description copied from interface:BlockingQueueRemoves 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 collectioncmay result in elements being in neither, either or both collections when the associated exception is thrown. Attempts to drain a queue to itself result inIllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.- Specified by:
drainToin interfaceBlockingQueue<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 collectionClassCastException- if the class of an element of this queue prevents it from being added to the specified collectionNullPointerException- if the specified collection is nullIllegalArgumentException- 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
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drainTo
public int drainTo(Collection<? super E> c, int maxElements)
Description copied from interface:BlockingQueueRemoves 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 collectioncmay result in elements being in neither, either or both collections when the associated exception is thrown. Attempts to drain a queue to itself result inIllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.- Specified by:
drainToin interfaceBlockingQueue<E>- Parameters:
c- the collection to transfer elements intomaxElements- 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 collectionClassCastException- if the class of an element of this queue prevents it from being added to the specified collectionNullPointerException- if the specified collection is nullIllegalArgumentException- 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
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iterator
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.
- Specified by:
iteratorin interfaceCollection<E>- Specified by:
iteratorin interfaceIterable<E>- Specified by:
iteratorin classAbstractCollection<E>- Returns:
- an iterator over the elements in this queue in proper sequence
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spliterator
public Spliterator<E> spliterator()
Returns aSpliteratorover the elements in this queue.The returned spliterator is weakly consistent.
The
SpliteratorreportsSpliterator.CONCURRENT,Spliterator.ORDERED, andSpliterator.NONNULL.- Specified by:
spliteratorin interfaceCollection<E>- Specified by:
spliteratorin interfaceIterable<E>- Implementation Note:
- The
SpliteratorimplementstrySplitto permit limited parallelism. - Returns:
- a
Spliteratorover the elements in this queue - Since:
- 1.8
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forEach
public void forEach(Consumer<? super E> action)
Description copied from interface:IterablePerforms the given action for each element of theIterableuntil all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions thrown by the action are relayed to the caller.The behavior of this method is unspecified if the action performs side-effects that modify the underlying source of elements, unless an overriding class has specified a concurrent modification policy.
- Specified by:
forEachin interfaceIterable<E>- Parameters:
action- The action to be performed for each element- Throws:
NullPointerException- if the specified action is null
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removeIf
public boolean removeIf(Predicate<? super E> filter)
Description copied from interface:CollectionRemoves 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.- Specified by:
removeIfin interfaceCollection<E>- Parameters:
filter- a predicate which returnstruefor elements to be removed- Returns:
trueif any elements were removed- Throws:
NullPointerException- if the specified filter is null
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removeAll
public boolean removeAll(Collection<?> c)
Description copied from class:AbstractCollectionRemoves 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.- Specified by:
removeAllin interfaceCollection<E>- Overrides:
removeAllin classAbstractCollection<E>- Parameters:
c- collection containing elements to be removed from this collection- Returns:
trueif this collection changed as a result of the call- Throws:
NullPointerException- if this collection contains one or more null elements and the specified collection does not support null elements (optional), or if the specified collection is null- See Also:
AbstractCollection.remove(Object),AbstractCollection.contains(Object)
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retainAll
public boolean retainAll(Collection<?> c)
Description copied from class:AbstractCollectionRetains 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.- Specified by:
retainAllin interfaceCollection<E>- Overrides:
retainAllin classAbstractCollection<E>- Parameters:
c- collection containing elements to be retained in this collection- Returns:
trueif this collection changed as a result of the call- Throws:
NullPointerException- if this collection contains one or more null elements and the specified collection does not permit null elements (optional), or if the specified collection is null- See Also:
AbstractCollection.remove(Object),AbstractCollection.contains(Object)
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