- Type Parameters:
E
- the type of elements held in this queue
- All Implemented Interfaces:
Serializable
,Iterable<E>
,Collection<E>
,BlockingQueue<E>
,Queue<E>
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:
-
Constructor Summary
ConstructorDescriptionArrayBlockingQueue
(int capacity) Creates anArrayBlockingQueue
with the given (fixed) capacity and default access policy.ArrayBlockingQueue
(int capacity, boolean fair) Creates anArrayBlockingQueue
with the given (fixed) capacity and the specified access policy.ArrayBlockingQueue
(int capacity, boolean fair, Collection<? extends E> c) Creates anArrayBlockingQueue
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 TypeMethodDescriptionboolean
Inserts the specified element at the tail of this queue if it is possible to do so immediately without exceeding the queue's capacity, returningtrue
upon success and throwing anIllegalStateException
if this queue is full.void
clear()
Atomically removes all of the elements from this queue.boolean
Returnstrue
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
Performs the given action for each element of theIterable
until all elements have been processed or the action throws an exception.iterator()
Returns an iterator over the elements in this queue in proper sequence.boolean
Inserts the specified element at the tail of this queue if it is possible to do so immediately without exceeding the queue's capacity, returningtrue
upon success andfalse
if this queue is full.boolean
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.peek()
Retrieves, but does not remove, the head of this queue, or returnsnull
if this queue is empty.poll()
Retrieves and removes the head of this queue, or returnsnull
if this queue is empty.Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.void
Inserts the specified element at the tail of this queue, waiting for space to become available if the queue is full.int
Returns the number of additional elements that this queue can ideally (in the absence of memory or resource constraints) accept without blocking.boolean
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
Removes all of the elements of this collection that satisfy the given predicate (optional operation).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.Returns aSpliterator
over the elements in this queue.take()
Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.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.Collection
addAll, containsAll, equals, hashCode, isEmpty, parallelStream, stream, toArray
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Constructor Details
-
ArrayBlockingQueue
public ArrayBlockingQueue(int capacity) Creates anArrayBlockingQueue
with the given (fixed) capacity and default access policy.- Parameters:
capacity
- the capacity of this queue- Throws:
IllegalArgumentException
- ifcapacity < 1
-
ArrayBlockingQueue
public ArrayBlockingQueue(int capacity, boolean fair) Creates anArrayBlockingQueue
with the given (fixed) capacity and the specified access policy.- Parameters:
capacity
- the capacity of this queuefair
- iftrue
then queue accesses for threads blocked on insertion or removal, are processed in FIFO order; iffalse
the access order is unspecified.- Throws:
IllegalArgumentException
- ifcapacity < 1
-
ArrayBlockingQueue
Creates anArrayBlockingQueue
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 queuefair
- iftrue
then queue accesses for threads blocked on insertion or removal, are processed in FIFO order; iffalse
the access order is unspecified.c
- the collection of elements to initially contain- Throws:
IllegalArgumentException
- ifcapacity
is less thanc.size()
, or less than 1.NullPointerException
- if the specified collection or any of its elements are null
-
-
Method Details
-
add
Inserts the specified element at the tail of this queue if it is possible to do so immediately without exceeding the queue's capacity, returningtrue
upon success and throwing anIllegalStateException
if this queue is full.- Specified by:
add
in interfaceBlockingQueue<E>
- Specified by:
add
in interfaceCollection<E>
- Specified by:
add
in interfaceQueue<E>
- Overrides:
add
in 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
-
offer
Inserts the specified element at the tail of this queue if it is possible to do so immediately without exceeding the queue's capacity, returningtrue
upon success andfalse
if 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:
offer
in interfaceBlockingQueue<E>
- Specified by:
offer
in interfaceQueue<E>
- Parameters:
e
- the element to add- Returns:
true
if the element was added to this queue, elsefalse
- Throws:
NullPointerException
- if the specified element is null
-
put
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 interfaceBlockingQueue<E>
- Parameters:
e
- the element to add- Throws:
InterruptedException
- if interrupted while waitingNullPointerException
- if the specified element is null
-
offer
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 interfaceBlockingQueue<E>
- Parameters:
e
- the element to addtimeout
- how long to wait before giving up, in units ofunit
unit
- aTimeUnit
determining how to interpret thetimeout
parameter- Returns:
true
if successful, orfalse
if the specified waiting time elapses before space is available- Throws:
InterruptedException
- if interrupted while waitingNullPointerException
- if the specified element is null
-
poll
-
take
Description copied from interface:BlockingQueue
Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.- Specified by:
take
in interfaceBlockingQueue<E>
- Returns:
- the head of this queue
- Throws:
InterruptedException
- if interrupted while waiting
-
poll
Description copied from interface:BlockingQueue
Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.- Specified by:
poll
in interfaceBlockingQueue<E>
- Parameters:
timeout
- how long to wait before giving up, in units ofunit
unit
- aTimeUnit
determining how to interpret thetimeout
parameter- Returns:
- the head of this queue, or
null
if the specified waiting time elapses before an element is available - Throws:
InterruptedException
- if interrupted while waiting
-
peek
-
size
public int size()Returns the number of elements in this queue.- Specified by:
size
in interfaceCollection<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 currentsize
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 interfaceBlockingQueue<E>
- Returns:
- the remaining capacity
-
remove
Removes a single instance of the specified element from this queue, if it is present. More formally, removes an elemente
such thato.equals(e)
, if this queue contains one or more such elements. Returnstrue
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 interfaceBlockingQueue<E>
- Specified by:
remove
in interfaceCollection<E>
- Overrides:
remove
in classAbstractCollection<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
Returnstrue
if this queue contains the specified element. More formally, returnstrue
if and only if this queue contains at least one elemente
such thato.equals(e)
.- Specified by:
contains
in interfaceBlockingQueue<E>
- Specified by:
contains
in interfaceCollection<E>
- Overrides:
contains
in classAbstractCollection<E>
- Parameters:
o
- object to be checked for containment in this queue- Returns:
true
if this queue contains the specified element
-
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 interfaceCollection<E>
- Overrides:
toArray
in classAbstractCollection<E>
- Returns:
- an array containing all of the elements in this queue
-
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
x
is a queue known to contain only strings. The following code can be used to dump the queue into a newly allocated array ofString
:String[] y = x.toArray(new String[0]);
toArray(new Object[0])
is identical in function totoArray()
.- Specified by:
toArray
in interfaceCollection<E>
- Overrides:
toArray
in 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
-
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 interfaceCollection<E>
- Overrides:
clear
in classAbstractQueue<E>
-
drainTo
Description copied from interface:BlockingQueue
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 collectionc
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 inIllegalArgumentException
. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.- Specified by:
drainTo
in 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
-
drainTo
Description copied from interface:BlockingQueue
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 collectionc
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 inIllegalArgumentException
. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.- Specified by:
drainTo
in 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
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:
iterator
in interfaceCollection<E>
- Specified by:
iterator
in interfaceIterable<E>
- Specified by:
iterator
in classAbstractCollection<E>
- Returns:
- an iterator over the elements in this queue in proper sequence
-
spliterator
Returns aSpliterator
over the elements in this queue.The returned spliterator is weakly consistent.
The
Spliterator
reportsSpliterator.CONCURRENT
,Spliterator.ORDERED
, andSpliterator.NONNULL
.- Specified by:
spliterator
in interfaceCollection<E>
- Specified by:
spliterator
in interfaceIterable<E>
- Implementation Note:
- The
Spliterator
implementstrySplit
to permit limited parallelism. - Returns:
- a
Spliterator
over the elements in this queue - Since:
- 1.8
-
forEach
Description copied from interface:Iterable
Performs the given action for each element of theIterable
until 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:
forEach
in interfaceIterable<E>
- Parameters:
action
- The action to be performed for each element- Throws:
NullPointerException
- if the specified action is null
-
removeIf
Description copied from interface:Collection
Removes all of the elements of this collection that satisfy the given predicate (optional operation). Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller.- Specified by:
removeIf
in interfaceCollection<E>
- Parameters:
filter
- a predicate which returnstrue
for elements to be removed- Returns:
true
if any elements were removed- Throws:
NullPointerException
- if the specified filter is null
-
removeAll
Description copied from class:AbstractCollection
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.- Specified by:
removeAll
in interfaceCollection<E>
- Overrides:
removeAll
in classAbstractCollection<E>
- Parameters:
c
- collection containing elements to be removed from this collection- Returns:
true
if 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:
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retainAll
Description copied from class:AbstractCollection
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.- Specified by:
retainAll
in interfaceCollection<E>
- Overrides:
retainAll
in classAbstractCollection<E>
- Parameters:
c
- collection containing elements to be retained in this collection- Returns:
true
if 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:
-