- java.lang.Object
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- java.util.AbstractCollection<E>
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- java.util.AbstractQueue<E>
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- java.util.concurrent.SynchronousQueue<E>
 
 
 
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- Type Parameters:
- E- the type of elements held in this queue
 - All Implemented Interfaces:
- Serializable,- Iterable<E>,- Collection<E>,- BlockingQueue<E>,- Queue<E>
 
 public class SynchronousQueue<E> extends AbstractQueue<E> implements BlockingQueue<E>, Serializable 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 cannotpeekat 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 andpoll()will returnnull. For purposes of otherCollectionmethods (for examplecontains), aSynchronousQueueacts as an empty collection. This queue does not permitnullelements.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 truegrants threads access in FIFO order.This class and its iterator implement all of the optional methods of the CollectionandIteratorinterfaces.This class is a member of the Java Collections Framework. - Since:
- 1.5
- See Also:
- Serialized Form
 
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Constructor SummaryConstructors Constructor Description SynchronousQueue()Creates aSynchronousQueuewith nonfair access policy.SynchronousQueue(boolean fair)Creates aSynchronousQueuewith the specified fairness policy.
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Method SummaryAll Methods Instance Methods Concrete Methods Modifier and Type Method Description voidclear()Does nothing.booleancontains(Object o)Always 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<E>iterator()Returns an empty iterator in whichhasNextalways returnsfalse.booleanoffer(E e)Inserts the specified element into this queue, if another thread is waiting to receive it.booleanoffer(E e, long timeout, TimeUnit unit)Inserts the specified element into this queue, waiting if necessary up to the specified wait time for another thread to receive it.Epeek()Always returnsnull.Epoll()Retrieves and removes the head of this queue, if another thread is currently making an element available.Epoll(long timeout, TimeUnit unit)Retrieves and removes the head of this queue, waiting if necessary up to the specified wait time, for another thread to insert it.voidput(E e)Adds the specified element to this queue, waiting if necessary for another thread to receive it.intremainingCapacity()Always returns zero.booleanremove(Object o)Always returnsfalse.booleanremoveAll(Collection<?> c)Always returnsfalse.booleanretainAll(Collection<?> c)Always returnsfalse.intsize()Always returns zero.Spliterator<E>spliterator()Returns an empty spliterator in which calls totrySplitalways returnnull.Etake()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.StringtoString()Always returns"[]".- 
Methods declared in class java.util.AbstractQueueadd, addAll, element, remove
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Methods declared in class java.lang.Objectclone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
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Methods declared in interface java.util.concurrent.BlockingQueueadd
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Methods declared in interface java.util.CollectionaddAll, equals, hashCode, parallelStream, removeIf, stream, toArray
 
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Constructor Detail- 
SynchronousQueuepublic SynchronousQueue() Creates aSynchronousQueuewith nonfair access policy.
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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 Detail- 
putpublic void put(E e) throws InterruptedException Adds 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
 
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offerpublic boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException Inserts 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
 
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offerpublic boolean offer(E e) Inserts 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
 
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takepublic E take() throws InterruptedException Retrieves 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
 
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pollpublic E poll(long timeout, TimeUnit unit) throws InterruptedException Retrieves 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
 
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pollpublic E poll() Retrieves and removes the head of this queue, if another thread is currently making an element available.
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isEmptypublic boolean isEmpty() Always returnstrue. ASynchronousQueuehas no internal capacity.- Specified by:
- isEmptyin interface- Collection<E>
- Overrides:
- isEmptyin class- AbstractCollection<E>
- Returns:
- true
 
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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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containspublic boolean contains(Object o) Always 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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removepublic boolean remove(Object o) Always 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
 
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containsAllpublic boolean containsAll(Collection<?> c) Returnsfalseunless 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:
- AbstractCollection.contains(Object)
 
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removeAllpublic boolean removeAll(Collection<?> c) Always returnsfalse. ASynchronousQueuehas no internal capacity.- Specified by:
- removeAllin interface- Collection<E>
- Overrides:
- removeAllin class- AbstractCollection<E>
- Parameters:
- c- the collection
- Returns:
- false
- See Also:
- AbstractCollection.remove(Object),- AbstractCollection.contains(Object)
 
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retainAllpublic boolean retainAll(Collection<?> c) Always returnsfalse. ASynchronousQueuehas no internal capacity.- Specified by:
- retainAllin interface- Collection<E>
- Overrides:
- retainAllin class- AbstractCollection<E>
- Parameters:
- c- the collection
- Returns:
- false
- See Also:
- AbstractCollection.remove(Object),- AbstractCollection.contains(Object)
 
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peekpublic E peek() Always returnsnull. ASynchronousQueuedoes not return elements unless actively waited on.
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iteratorpublic Iterator<E> iterator() Returns 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
 
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spliteratorpublic Spliterator<E> spliterator() Returns 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
 
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toArraypublic Object[] toArray() Returns a zero-length array.- Specified by:
- toArrayin interface- Collection<E>
- Overrides:
- toArrayin class- AbstractCollection<E>
- Returns:
- a zero-length array
 
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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
 
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toStringpublic String toString() Always returns"[]".- Overrides:
- toStringin class- AbstractCollection<E>
- Returns:
- "[]"
 
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drainTopublic int drainTo(Collection<? super E> c) 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 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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drainTopublic int drainTo(Collection<? super E> c, int maxElements) 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 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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