- Type Parameters:
E- the type of elements held in this queue
- All Implemented Interfaces:
Serializable,Iterable<E>,Collection<E>,BlockingQueue<E>,TransferQueue<E>,Queue<E>
TransferQueue based on linked nodes.
This queue orders elements FIFO (first-in-first-out) with respect
to any given producer. The head of the queue is that
element that has been on the queue the longest time for some
producer. The tail of the queue is that element that has
been on the queue the shortest time for some producer.
Beware that, unlike in most collections, the size method
is NOT a constant-time operation. Because of the
asynchronous nature of these queues, determining the current number
of elements requires a traversal of the elements, and so may report
inaccurate results if this collection is modified during traversal.
Bulk operations that add, remove, or examine multiple elements,
such as AbstractQueue.addAll(java.util.Collection<? extends E>), removeIf(java.util.function.Predicate<? super E>) or forEach(java.util.function.Consumer<? super E>),
are not guaranteed to be performed atomically.
For example, a forEach traversal concurrent with an
addAll operation might observe only some of the added elements.
This class and its iterator implement all of the optional
methods of the Collection and Iterator interfaces.
Memory consistency effects: As with other concurrent
collections, actions in a thread prior to placing an object into a
LinkedTransferQueue
happen-before
actions subsequent to the access or removal of that element from
the LinkedTransferQueue in another thread.
This class is a member of the Java Collections Framework.
- Since:
- 1.7
- See Also:
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Constructor Summary
ConstructorsConstructorDescriptionCreates an initially emptyLinkedTransferQueue.LinkedTransferQueue(Collection<? extends E> c) Creates aLinkedTransferQueueinitially containing the elements of the given collection, added in traversal order of the collection's iterator. -
Method Summary
Modifier and TypeMethodDescriptionbooleanInserts the specified element at the tail of this queue.voidclear()Removes all of the elements from this queue.booleanReturnstrueif 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.voidPerforms the given action for each element of theIterableuntil all elements have been processed or the action throws an exception.intReturns an estimate of the number of consumers waiting to receive elements viaBlockingQueue.take()or timedpoll.booleanReturnstrueif there is at least one consumer waiting to receive an element viaBlockingQueue.take()or timedpoll.booleanisEmpty()Returnstrueif this queue contains no elements.iterator()Returns an iterator over the elements in this queue in proper sequence.booleanInserts the specified element at the tail of this queue.booleanInserts the specified element at the tail of this queue.peek()Retrieves, but does not remove, the head of this queue, or returnsnullif this queue is empty.poll()Retrieves and removes the head of this queue, or returnsnullif 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.voidInserts the specified element at the tail of this queue.intAlways returnsInteger.MAX_VALUEbecause aLinkedTransferQueueis not capacity constrained.booleanRemoves 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).booleanRemoves 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.Returns aSpliteratorover 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.voidTransfers the element to a consumer, waiting if necessary to do so.booleantryTransfer(E e) Transfers the element to a waiting consumer immediately, if possible.booleantryTransfer(E e, long timeout, TimeUnit unit) Transfers the element to a consumer if it is possible to do so before the timeout elapses.Methods declared in class java.util.AbstractQueue
addAll, clear, element, removeMethods declared in class java.util.AbstractCollection
containsAll, toStringMethods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, waitMethods declared in interface java.util.Collection
addAll, containsAll, equals, hashCode, parallelStream, stream, toArray
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Constructor Details
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LinkedTransferQueue
public LinkedTransferQueue()Creates an initially emptyLinkedTransferQueue. -
LinkedTransferQueue
Creates aLinkedTransferQueueinitially containing the elements of the given collection, added in traversal order of the collection's iterator.- Parameters:
c- the collection of elements to initially contain- Throws:
NullPointerException- if the specified collection or any of its elements are null
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Method Details
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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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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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put
Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never block.- Specified by:
putin interfaceBlockingQueue<E>- Parameters:
e- the element to add- Throws:
NullPointerException- if the specified element is null
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offer
Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never block or returnfalse.- 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:
true(as specified byBlockingQueue.offer)- Throws:
NullPointerException- if the specified element is null
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offer
Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never returnfalse.- Specified by:
offerin interfaceBlockingQueue<E>- Specified by:
offerin interfaceQueue<E>- Parameters:
e- the element to add- Returns:
true(as specified byQueue.offer(E))- Throws:
NullPointerException- if the specified element is null
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add
Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never throwIllegalStateExceptionor returnfalse.- 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:
NullPointerException- if the specified element is null
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tryTransfer
Transfers the element to a waiting consumer immediately, if possible.More precisely, transfers the specified element immediately if there exists a consumer already waiting to receive it (in
take()or timedpoll), otherwise returningfalsewithout enqueuing the element.- Specified by:
tryTransferin interfaceTransferQueue<E>- Parameters:
e- the element to transfer- Returns:
trueif the element was transferred, elsefalse- Throws:
NullPointerException- if the specified element is null
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transfer
Transfers the element to a consumer, waiting if necessary to do so.More precisely, transfers the specified element immediately if there exists a consumer already waiting to receive it (in
take()or timedpoll), else inserts the specified element at the tail of this queue and waits until the element is received by a consumer.- Specified by:
transferin interfaceTransferQueue<E>- Parameters:
e- the element to transfer- Throws:
NullPointerException- if the specified element is nullInterruptedException- if interrupted while waiting, in which case the element is not left enqueued
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tryTransfer
Transfers the element to a consumer if it is possible to do so before the timeout elapses.More precisely, transfers the specified element immediately if there exists a consumer already waiting to receive it (in
take()or timedpoll), else inserts the specified element at the tail of this queue and waits until the element is received by a consumer, returningfalseif the specified wait time elapses before the element can be transferred.- Specified by:
tryTransferin interfaceTransferQueue<E>- Parameters:
e- the element to transfertimeout- 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 completion, in which case the element is not left enqueued- Throws:
NullPointerException- if the specified element is nullInterruptedException- if interrupted while waiting, in which case the element is not left enqueued
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take
Description copied from interface:BlockingQueueRetrieves and removes the head of this queue, waiting if necessary until an element becomes available.- Specified by:
takein interfaceBlockingQueue<E>- Returns:
- the head of this queue
- Throws:
InterruptedException- if interrupted while waiting
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poll
Description copied from interface:BlockingQueueRetrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.- Specified by:
pollin interfaceBlockingQueue<E>- Parameters:
timeout- how long to wait before giving up, in units ofunitunit- aTimeUnitdetermining how to interpret thetimeoutparameter- Returns:
- the head of this queue, or
nullif the specified waiting time elapses before an element is available - Throws:
InterruptedException- if interrupted while waiting
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poll
Description copied from interface:QueueRetrieves and removes the head of this queue, or returnsnullif this queue is empty. -
drainTo
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:
NullPointerException- 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
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:
NullPointerException- 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:
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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peek
Description copied from interface:QueueRetrieves, but does not remove, the head of this queue, or returnsnullif this queue is empty. -
isEmpty
public boolean isEmpty()Returnstrueif this queue contains no elements.- Specified by:
isEmptyin interfaceCollection<E>- Overrides:
isEmptyin classAbstractCollection<E>- Returns:
trueif this queue contains no elements
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hasWaitingConsumer
public boolean hasWaitingConsumer()Description copied from interface:TransferQueueReturnstrueif there is at least one consumer waiting to receive an element viaBlockingQueue.take()or timedpoll. The return value represents a momentary state of affairs.- Specified by:
hasWaitingConsumerin interfaceTransferQueue<E>- Returns:
trueif there is at least one waiting consumer
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size
public int size()Returns the number of elements in this queue. If this queue contains more thanInteger.MAX_VALUEelements, returnsInteger.MAX_VALUE.Beware that, unlike in most collections, this method is NOT a constant-time operation. Because of the asynchronous nature of these queues, determining the current number of elements requires an O(n) traversal.
- Specified by:
sizein interfaceCollection<E>- Returns:
- the number of elements in this queue
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getWaitingConsumerCount
public int getWaitingConsumerCount()Description copied from interface:TransferQueueReturns an estimate of the number of consumers waiting to receive elements viaBlockingQueue.take()or timedpoll. The return value is an approximation of a momentary state of affairs, that may be inaccurate if consumers have completed or given up waiting. The value may be useful for monitoring and heuristics, but not for synchronization control. Implementations of this method are likely to be noticeably slower than those forTransferQueue.hasWaitingConsumer().- Specified by:
getWaitingConsumerCountin interfaceTransferQueue<E>- Returns:
- the number of consumers waiting to receive elements
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remove
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).- 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
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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remainingCapacity
public int remainingCapacity()Always returnsInteger.MAX_VALUEbecause aLinkedTransferQueueis not capacity constrained.- Specified by:
remainingCapacityin interfaceBlockingQueue<E>- Returns:
Integer.MAX_VALUE(as specified byBlockingQueue.remainingCapacity())
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removeIf
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
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:
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retainAll
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:
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clear
public void clear()Description copied from class:AbstractQueueRemoves all of the elements from this queue. The queue will be empty after this call returns.This implementation repeatedly invokes
polluntil it returnsnull.- Specified by:
clearin interfaceCollection<E>- Overrides:
clearin classAbstractQueue<E>
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forEach
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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