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- Type Parameters:
- E- the type of elements held in this queue
 - All Superinterfaces:
- BlockingQueue<E>,- Collection<E>,- Iterable<E>,- Queue<E>
 - All Known Implementing Classes:
- LinkedTransferQueue
 
 public interface TransferQueue<E> extends BlockingQueue<E> ABlockingQueuein which producers may wait for consumers to receive elements. ATransferQueuemay be useful for example in message passing applications in which producers sometimes (using methodtransfer(E)) await receipt of elements by consumers invokingtakeorpoll, while at other times enqueue elements (via methodput) without waiting for receipt. Non-blocking and time-out versions oftryTransferare also available. ATransferQueuemay also be queried, viahasWaitingConsumer(), whether there are any threads waiting for items, which is a converse analogy to apeekoperation.Like other blocking queues, a TransferQueuemay be capacity bounded. If so, an attempted transfer operation may initially block waiting for available space, and/or subsequently block waiting for reception by a consumer. Note that in a queue with zero capacity, such asSynchronousQueue,putandtransferare effectively synonymous.This interface is a member of the Java Collections Framework. - Since:
- 1.7
 
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Method SummaryAll Methods Instance Methods Abstract Methods Modifier and Type Method Description intgetWaitingConsumerCount()Returns an estimate of the number of consumers waiting to receive elements viaBlockingQueue.take()or timedpoll.booleanhasWaitingConsumer()Returnstrueif there is at least one consumer waiting to receive an element viaBlockingQueue.take()or timedpoll.voidtransfer(E e)Transfers 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 interface java.util.concurrent.BlockingQueueadd, contains, drainTo, drainTo, offer, offer, poll, put, remainingCapacity, remove, take
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Methods declared in interface java.util.CollectionaddAll, clear, containsAll, equals, hashCode, isEmpty, iterator, parallelStream, removeAll, removeIf, retainAll, size, spliterator, stream, toArray, toArray, toArray
 
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Method Detail- 
tryTransferboolean tryTransfer(E e) 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 BlockingQueue.take()or timedpoll), otherwise returningfalsewithout enqueuing the element.- Parameters:
- e- the element to transfer
- Returns:
- trueif the element was transferred, else- false
- Throws:
- ClassCastException- if the class of the specified element prevents it from being added to this queue
- NullPointerException- if the specified element is null
- IllegalArgumentException- if some property of the specified element prevents it from being added to this queue
 
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transfervoid transfer(E e) throws InterruptedException 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 BlockingQueue.take()or timedpoll), else waits until the element is received by a consumer.- Parameters:
- e- the element to transfer
- Throws:
- InterruptedException- if interrupted while waiting, in which case the element is not left enqueued
- ClassCastException- if the class of the specified element prevents it from being added to this queue
- NullPointerException- if the specified element is null
- IllegalArgumentException- if some property of the specified element prevents it from being added to this queue
 
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tryTransferboolean tryTransfer(E e, long timeout, TimeUnit unit) throws InterruptedException 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 BlockingQueue.take()or timedpoll), else waits until the element is received by a consumer, returningfalseif the specified wait time elapses before the element can be transferred.- Parameters:
- e- the element to transfer
- timeout- how long to wait before giving up, in units of- unit
- unit- a- TimeUnitdetermining how to interpret the- timeoutparameter
- Returns:
- trueif successful, or- falseif the specified waiting time elapses before completion, in which case the element is not left enqueued
- Throws:
- InterruptedException- if interrupted while waiting, in which case the element is not left enqueued
- ClassCastException- if the class of the specified element prevents it from being added to this queue
- NullPointerException- if the specified element is null
- IllegalArgumentException- if some property of the specified element prevents it from being added to this queue
 
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hasWaitingConsumerboolean hasWaitingConsumer() Returnstrueif there is at least one consumer waiting to receive an element viaBlockingQueue.take()or timedpoll. The return value represents a momentary state of affairs.- Returns:
- trueif there is at least one waiting consumer
 
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getWaitingConsumerCountint getWaitingConsumerCount() Returns 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 forhasWaitingConsumer().- Returns:
- the number of consumers waiting to receive elements
 
 
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