java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractQueue<E>
java.util.concurrent.SynchronousQueue<E>
- Type Parameters:
- E- the type of elements held in this queue
- All Implemented Interfaces:
- Serializable,- Iterable<E>,- Collection<E>,- BlockingQueue<E>,- Queue<E>
A blocking queue in which each insert
 operation must wait for a corresponding remove operation by another
 thread, and vice versa.  A synchronous queue does not have any
 internal capacity, not even a capacity of one.  You cannot
 
peek at a synchronous queue because an element is only
 present when you try to remove it; you cannot insert an element
 (using any method) unless another thread is trying to remove it;
 you cannot iterate as there is nothing to iterate.  The
 head of the queue is the element that the first queued
 inserting thread is trying to add to the queue; if there is no such
 queued thread then no element is available for removal and
 poll() will return null.  For purposes of other
 Collection methods (for example contains), a
 SynchronousQueue acts as an empty collection.  This queue
 does not permit null elements.
 Synchronous queues are similar to rendezvous channels used in CSP and Ada. They are well suited for handoff designs, in which an object running in one thread must sync up with an object running in another thread in order to hand it some information, event, or task.
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.
 
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 SummaryConstructorsConstructorDescriptionCreates aSynchronousQueuewith nonfair access policy.SynchronousQueue(boolean fair) Creates aSynchronousQueuewith the specified fairness policy.
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Method SummaryModifier and TypeMethodDescriptionvoidclear()Does nothing.booleanAlways returnsfalse.booleancontainsAll(Collection<?> c) Returnsfalseunless the given collection is empty.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.booleanisEmpty()Always returnstrue.iterator()Returns an empty iterator in whichhasNextalways returnsfalse.booleanInserts the specified element into this queue, if another thread is waiting to receive it.booleanInserts the specified element into this queue, waiting if necessary up to the specified wait time for another thread to receive it.peek()Always returnsnull.poll()Retrieves and removes the head of this queue, if another thread is currently making an element available.Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time, for another thread to insert it.voidAdds the specified element to this queue, waiting if necessary for another thread to receive it.intAlways returns zero.booleanAlways returnsfalse.booleanremoveAll(Collection<?> c) Always returnsfalse.booleanretainAll(Collection<?> c) Always returnsfalse.intsize()Always returns zero.Returns an empty spliterator in which calls totrySplitalways returnnull.take()Retrieves and removes the head of this queue, waiting if necessary for another thread to insert it.Object[]toArray()Returns a zero-length array.<T> T[]toArray(T[] a) Sets the zeroth element of the specified array tonull(if the array has non-zero length) and returns it.toString()Always returns"[]".Methods declared in class java.util.AbstractQueueadd, addAll, element, removeMethods declared in class java.lang.Objectclone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, waitMethods declared in interface java.util.concurrent.BlockingQueueaddMethods declared in interface java.util.CollectionaddAll, equals, hashCode, parallelStream, removeIf, stream, toArray
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Constructor Details- 
SynchronousQueuepublic SynchronousQueue()Creates aSynchronousQueuewith nonfair access policy.
- 
SynchronousQueuepublic SynchronousQueue(boolean fair) Creates aSynchronousQueuewith the specified fairness policy.- Parameters:
- fair- if true, waiting threads contend in FIFO order for access; otherwise the order is unspecified.
 
 
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- 
Method Details- 
putAdds the specified element to this queue, waiting if necessary for another thread to receive it.- Specified by:
- putin interface- BlockingQueue<E>
- Parameters:
- e- the element to add
- Throws:
- InterruptedException- if interrupted while waiting
- NullPointerException- if the specified element is null
 
- 
offerInserts the specified element into this queue, waiting if necessary up to the specified wait time for another thread to receive it.- Specified by:
- offerin interface- BlockingQueue<E>
- Parameters:
- e- the element to add
- 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 a consumer appears
- Throws:
- InterruptedException- if interrupted while waiting
- NullPointerException- if the specified element is null
 
- 
offerInserts the specified element into this queue, if another thread is waiting to receive it.- Specified by:
- offerin interface- BlockingQueue<E>
- Specified by:
- offerin interface- Queue<E>
- Parameters:
- e- the element to add
- Returns:
- trueif the element was added to this queue, else- false
- Throws:
- NullPointerException- if the specified element is null
 
- 
takeRetrieves and removes the head of this queue, waiting if necessary for another thread to insert it.- Specified by:
- takein interface- BlockingQueue<E>
- Returns:
- the head of this queue
- Throws:
- InterruptedException- if interrupted while waiting
 
- 
pollRetrieves and removes the head of this queue, waiting if necessary up to the specified wait time, for another thread to insert it.- Specified by:
- pollin interface- BlockingQueue<E>
- Parameters:
- timeout- how long to wait before giving up, in units of- unit
- unit- a- TimeUnitdetermining how to interpret the- timeoutparameter
- Returns:
- the head of this queue, or nullif the specified waiting time elapses before an element is present
- Throws:
- InterruptedException- if interrupted while waiting
 
- 
pollRetrieves and removes the head of this queue, if another thread is currently making an element available.
- 
isEmptypublic boolean isEmpty()Always returnstrue. ASynchronousQueuehas no internal capacity.- Specified by:
- isEmptyin interface- Collection<E>
- Overrides:
- isEmptyin class- AbstractCollection<E>
- Returns:
- true
 
- 
sizepublic int size()Always returns zero. ASynchronousQueuehas no internal capacity.- Specified by:
- sizein interface- Collection<E>
- Returns:
- zero
 
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remainingCapacitypublic int remainingCapacity()Always returns zero. ASynchronousQueuehas no internal capacity.- Specified by:
- remainingCapacityin interface- BlockingQueue<E>
- Returns:
- zero
 
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clearpublic void clear()Does nothing. ASynchronousQueuehas no internal capacity.- Specified by:
- clearin interface- Collection<E>
- Overrides:
- clearin class- AbstractQueue<E>
 
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containsAlways returnsfalse. ASynchronousQueuehas no internal capacity.- Specified by:
- containsin interface- BlockingQueue<E>
- Specified by:
- containsin interface- Collection<E>
- Overrides:
- containsin class- AbstractCollection<E>
- Parameters:
- o- the element
- Returns:
- false
 
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removeAlways returnsfalse. ASynchronousQueuehas no internal capacity.- Specified by:
- removein interface- BlockingQueue<E>
- Specified by:
- removein interface- Collection<E>
- Overrides:
- removein class- AbstractCollection<E>
- Parameters:
- o- the element to remove
- Returns:
- false
 
- 
containsAllReturnsfalseunless the given collection is empty. ASynchronousQueuehas no internal capacity.- Specified by:
- containsAllin interface- Collection<E>
- Overrides:
- containsAllin class- AbstractCollection<E>
- Parameters:
- c- the collection
- Returns:
- falseunless given collection is empty
- See Also:
 
- 
removeAllAlways returnsfalse. ASynchronousQueuehas no internal capacity.- Specified by:
- removeAllin interface- Collection<E>
- Overrides:
- removeAllin class- AbstractCollection<E>
- Parameters:
- c- the collection
- Returns:
- false
- See Also:
 
- 
retainAllAlways returnsfalse. ASynchronousQueuehas no internal capacity.- Specified by:
- retainAllin interface- Collection<E>
- Overrides:
- retainAllin class- AbstractCollection<E>
- Parameters:
- c- the collection
- Returns:
- false
- See Also:
 
- 
peekAlways returnsnull. ASynchronousQueuedoes not return elements unless actively waited on.
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iteratorReturns an empty iterator in whichhasNextalways returnsfalse.- Specified by:
- iteratorin interface- Collection<E>
- Specified by:
- iteratorin interface- Iterable<E>
- Specified by:
- iteratorin class- AbstractCollection<E>
- Returns:
- an empty iterator
 
- 
spliteratorReturns an empty spliterator in which calls totrySplitalways returnnull.- Specified by:
- spliteratorin interface- Collection<E>
- Specified by:
- spliteratorin interface- Iterable<E>
- Returns:
- an empty spliterator
- Since:
- 1.8
 
- 
toArrayReturns a zero-length array.- Specified by:
- toArrayin interface- Collection<E>
- Overrides:
- toArrayin class- AbstractCollection<E>
- Returns:
- a zero-length array
 
- 
toArraypublic <T> T[] toArray(T[] a) Sets the zeroth element of the specified array tonull(if the array has non-zero length) and returns it.- Specified by:
- toArrayin interface- Collection<E>
- Overrides:
- toArrayin class- AbstractCollection<E>
- Type Parameters:
- T- the component type of the array to contain the collection
- Parameters:
- a- the array
- Returns:
- the specified array
- Throws:
- NullPointerException- if the specified array is null
 
- 
toStringAlways returns"[]".- Overrides:
- toStringin class- AbstractCollection<E>
- Returns:
- "[]"
 
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drainToDescription 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 interface- BlockingQueue<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 collection
- ClassCastException- if the class of an element of this queue prevents it from being added to the specified collection
- NullPointerException- if the specified collection is null
- IllegalArgumentException- 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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drainToDescription 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 interface- BlockingQueue<E>
- Parameters:
- c- the collection to transfer elements into
- maxElements- 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 collection
- ClassCastException- if the class of an element of this queue prevents it from being added to the specified collection
- NullPointerException- if the specified collection is null
- IllegalArgumentException- 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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