- 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
BlockingQueue in which producers may wait for consumers
 to receive elements.  A TransferQueue may be useful for
 example in message passing applications in which producers
 sometimes (using method transfer(E)) await receipt of
 elements by consumers invoking take or poll, while
 at other times enqueue elements (via method put) without
 waiting for receipt.
 Non-blocking and
 time-out versions of
 tryTransfer are also available.
 A TransferQueue may also be queried, via hasWaitingConsumer(), whether there are any threads waiting for
 items, which is a converse analogy to a peek operation.
 Like other blocking queues, a TransferQueue may 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 as SynchronousQueue, put
 and transfer are effectively synonymous.
 
This interface is a member of the Java Collections Framework.
- Since:
- 1.7
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Method SummaryModifier and TypeMethodDescriptionintReturns 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.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 interface java.util.concurrent.BlockingQueueadd, contains, drainTo, drainTo, offer, offer, poll, put, remainingCapacity, remove, takeMethods 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 Details- 
tryTransferTransfers 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
 
- 
transferTransfers 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
 
- 
tryTransferTransfers 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
 
- 
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
 
- 
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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