E
- the type of elements held in this collectionpublic class ArrayBlockingQueue<E> extends AbstractQueue<E> implements BlockingQueue<E>, Serializable
A bounded blocking queue backed by an array. This queue orders elements FIFO (first-in-first-out). The head of the queue is that element that has been on the queue the longest time. The tail of the queue is that element that has been on the queue the shortest time. New elements are inserted at the tail of the queue, and the queue retrieval operations obtain elements at the head of the queue.
This is a classic "bounded buffer", in which a fixed-sized array holds elements inserted by producers and extracted by consumers. Once created, the capacity cannot be changed. Attempts to put
an element into a full queue will result in the operation blocking; attempts to take
an element from an empty queue will similarly block.
This class supports an optional fairness policy for ordering waiting producer and consumer threads. By default, this ordering is not guaranteed. However, a queue constructed with fairness set to true
grants threads access in FIFO order. Fairness generally decreases throughput but reduces variability and avoids starvation.
This class and its iterator implement all of the optional methods of the Collection
and Iterator
interfaces.
This class is a member of the Java Collections Framework.
public ArrayBlockingQueue(int capacity)
Creates an ArrayBlockingQueue
with the given (fixed) capacity and default access policy.
capacity
- the capacity of this queueIllegalArgumentException
- if capacity < 1
public ArrayBlockingQueue(int capacity, boolean fair)
Creates an ArrayBlockingQueue
with the given (fixed) capacity and the specified access policy.
capacity
- the capacity of this queuefair
- if true
then queue accesses for threads blocked on insertion or removal, are processed in FIFO order; if false
the access order is unspecified.IllegalArgumentException
- if capacity < 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.
capacity
- the capacity of this queuefair
- 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 containIllegalArgumentException
- if capacity
is less than c.size()
, or less than 1.NullPointerException
- if the specified collection or any of its elements are nullpublic 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.
add
in interface Collection<E>
add
in interface BlockingQueue<E>
add
in interface Queue<E>
add
in class AbstractQueue<E>
e
- the element to addtrue
(as specified by Collection.add(E)
)IllegalStateException
- if this queue is fullNullPointerException
- if the specified element is nullpublic 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.
offer
in interface BlockingQueue<E>
offer
in interface Queue<E>
e
- the element to addtrue
if the element was added to this queue, else false
NullPointerException
- if the specified element is nullpublic 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.
put
in interface BlockingQueue<E>
e
- the element to addInterruptedException
- if interrupted while waitingNullPointerException
- if the specified element is nullpublic 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.
offer
in interface BlockingQueue<E>
e
- the element to addtimeout
- how long to wait before giving up, in units of unit
unit
- a TimeUnit
determining how to interpret the timeout
parametertrue
if successful, or false
if the specified waiting time elapses before space is availableInterruptedException
- if interrupted while waitingNullPointerException
- if the specified element is nullpublic E poll()
Description copied from interface: Queue
Retrieves and removes the head of this queue, or returns null
if this queue is empty.
poll
in interface Queue<E>
null
if this queue is emptypublic E take() throws InterruptedException
Description copied from interface: BlockingQueue
Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.
take
in interface BlockingQueue<E>
InterruptedException
- if interrupted while waitingpublic E poll(long timeout, TimeUnit unit) throws InterruptedException
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.
poll
in interface BlockingQueue<E>
timeout
- how long to wait before giving up, in units of unit
unit
- a TimeUnit
determining how to interpret the timeout
parameternull
if the specified waiting time elapses before an element is availableInterruptedException
- if interrupted while waitingpublic E peek()
Description copied from interface: Queue
Retrieves, but does not remove, the head of this queue, or returns null
if this queue is empty.
peek
in interface Queue<E>
null
if this queue is emptypublic int size()
Returns the number of elements in this queue.
size
in interface Collection<E>
size
in class AbstractCollection<E>
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.
remainingCapacity
in interface BlockingQueue<E>
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.
remove
in interface Collection<E>
remove
in interface BlockingQueue<E>
remove
in class AbstractCollection<E>
o
- element to be removed from this queue, if presenttrue
if this queue changed as a result of the callpublic 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)
.
contains
in interface Collection<E>
contains
in interface BlockingQueue<E>
contains
in class AbstractCollection<E>
o
- object to be checked for containment in this queuetrue
if this queue contains the specified elementpublic 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.
toArray
in interface Collection<E>
toArray
in class AbstractCollection<E>
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 of String
:
String[] y = x.toArray(new String[0]);Note that
toArray(new Object[0])
is identical in function to toArray()
.toArray
in interface Collection<E>
toArray
in class AbstractCollection<E>
T
- the runtime type of the array to contain the collectiona
- 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 purposeArrayStoreException
- 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 nullpublic 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)
.
toString
in class AbstractCollection<E>
public void clear()
Atomically removes all of the elements from this queue. The queue will be empty after this call returns.
clear
in interface Collection<E>
clear
in class AbstractQueue<E>
public int drainTo(Collection<? super E> c)
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 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.
drainTo
in interface BlockingQueue<E>
c
- the collection to transfer elements intoUnsupportedOperationException
- 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 collectionpublic 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 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.
drainTo
in interface BlockingQueue<E>
c
- the collection to transfer elements intomaxElements
- the maximum number of elements to transferUnsupportedOperationException
- 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 collectionpublic 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.
iterator
in interface Iterable<E>
iterator
in interface Collection<E>
iterator
in class AbstractCollection<E>
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
.
spliterator
in interface Iterable<E>
spliterator
in interface Collection<E>
Spliterator
implements trySplit
to permit limited parallelism.Spliterator
over the elements in this queue
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