E - the type of elements held in this collectionpublic class SynchronousQueue<E> extends AbstractQueue<E> implements BlockingQueue<E>, Serializable
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.
| Constructor and Description |
|---|
SynchronousQueue()
Creates a
SynchronousQueue with nonfair access policy. |
SynchronousQueue(boolean fair)
Creates a
SynchronousQueue with the specified fairness policy. |
| Modifier and Type | Method and Description |
|---|---|
void |
clear()
Does nothing.
|
boolean |
contains(Object o)
Always returns
false. |
boolean |
containsAll(Collection<?> c)
Returns
false unless the given collection is empty. |
int |
drainTo(Collection<? super E> c)
Removes all available elements from this queue and adds them
to the given collection.
|
int |
drainTo(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.
|
boolean |
isEmpty()
Always returns
true. |
Iterator<E> |
iterator()
Returns an empty iterator in which
hasNext always returns
false. |
boolean |
offer(E e)
Inserts the specified element into this queue, if another thread is
waiting to receive it.
|
boolean |
offer(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.
|
E |
peek()
Always returns
null. |
E |
poll()
Retrieves and removes the head of this queue, if another thread
is currently making an element available.
|
E |
poll(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.
|
void |
put(E e)
Adds the specified element to this queue, waiting if necessary for
another thread to receive it.
|
int |
remainingCapacity()
Always returns zero.
|
boolean |
remove(Object o)
Always returns
false. |
boolean |
removeAll(Collection<?> c)
Always returns
false. |
boolean |
retainAll(Collection<?> c)
Always returns
false. |
int |
size()
Always returns zero.
|
Spliterator<E> |
spliterator()
Returns an empty spliterator in which calls to
Spliterator.trySplit() always return null. |
E |
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 zeroeth element of the specified array to
null
(if the array has non-zero length) and returns it. |
add, addAll, element, removetoStringclone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, waitaddaddAll, equals, hashCode, parallelStream, removeIf, streampublic SynchronousQueue()
SynchronousQueue with nonfair access policy.public SynchronousQueue(boolean fair)
SynchronousQueue with the specified fairness policy.fair - if true, waiting threads contend in FIFO order for
access; otherwise the order is unspecified.public void put(E e) throws InterruptedException
put in interface BlockingQueue<E>e - the element to addInterruptedException - if interrupted while waitingNullPointerException - if the specified element is nullpublic boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException
offer in interface BlockingQueue<E>e - the element to addtimeout - how long to wait before giving up, in units of
unitunit - a TimeUnit determining how to interpret the
timeout parametertrue if successful, or false if the
specified waiting time elapses before a consumer appearsInterruptedException - if interrupted while waitingNullPointerException - if the specified element is nullpublic boolean offer(E e)
offer in interface BlockingQueue<E>offer in interface Queue<E>e - the element to addtrue if the element was added to this queue, else
falseNullPointerException - if the specified element is nullpublic E take() throws InterruptedException
take in interface BlockingQueue<E>InterruptedException - if interrupted while waitingpublic E poll(long timeout, TimeUnit unit) throws InterruptedException
poll in interface BlockingQueue<E>timeout - how long to wait before giving up, in units of
unitunit - a TimeUnit determining how to interpret the
timeout parameternull if the
specified waiting time elapses before an element is presentInterruptedException - if interrupted while waitingpublic E poll()
public boolean isEmpty()
true.
A SynchronousQueue has no internal capacity.isEmpty in interface Collection<E>isEmpty in class AbstractCollection<E>truepublic int size()
SynchronousQueue has no internal capacity.size in interface Collection<E>size in class AbstractCollection<E>public int remainingCapacity()
SynchronousQueue has no internal capacity.remainingCapacity in interface BlockingQueue<E>public void clear()
SynchronousQueue has no internal capacity.clear in interface Collection<E>clear in class AbstractQueue<E>public boolean contains(Object o)
false.
A SynchronousQueue has no internal capacity.contains in interface Collection<E>contains in interface BlockingQueue<E>contains in class AbstractCollection<E>o - the elementfalsepublic boolean remove(Object o)
false.
A SynchronousQueue has no internal capacity.remove in interface Collection<E>remove in interface BlockingQueue<E>remove in class AbstractCollection<E>o - the element to removefalsepublic boolean containsAll(Collection<?> c)
false unless the given collection is empty.
A SynchronousQueue has no internal capacity.containsAll in interface Collection<E>containsAll in class AbstractCollection<E>c - the collectionfalse unless given collection is emptyAbstractCollection.contains(Object)public boolean removeAll(Collection<?> c)
false.
A SynchronousQueue has no internal capacity.removeAll in interface Collection<E>removeAll in class AbstractCollection<E>c - the collectionfalseAbstractCollection.remove(Object),
AbstractCollection.contains(Object)public boolean retainAll(Collection<?> c)
false.
A SynchronousQueue has no internal capacity.retainAll in interface Collection<E>retainAll in class AbstractCollection<E>c - the collectionfalseAbstractCollection.remove(Object),
AbstractCollection.contains(Object)public E peek()
null.
A SynchronousQueue does not return elements
unless actively waited on.public Iterator<E> iterator()
hasNext always returns
false.iterator in interface Iterable<E>iterator in interface Collection<E>iterator in class AbstractCollection<E>public Spliterator<E> spliterator()
Spliterator.trySplit() always return null.spliterator in interface Iterable<E>spliterator in interface Collection<E>public Object[] toArray()
toArray in interface Collection<E>toArray in class AbstractCollection<E>public <T> T[] toArray(T[] a)
null
(if the array has non-zero length) and returns it.toArray in interface Collection<E>toArray in class AbstractCollection<E>T - the runtime type of the array to contain the collectiona - the arrayNullPointerException - if the specified array is nullpublic int drainTo(Collection<? super E> c)
BlockingQueuec may result in elements being in neither,
either or both collections when the associated exception is
thrown. Attempts to drain a queue to itself result in
IllegalArgumentException. Further, the behavior of
this operation is undefined if the specified collection is
modified while the operation is in progress.drainTo in interface BlockingQueue<E>c - the collection to transfer elements intoUnsupportedOperationException - if addition of elements
is not supported by the specified collectionClassCastException - if the class of an element of this queue
prevents it from being added to the specified collectionNullPointerException - 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 collectionpublic int drainTo(Collection<? super E> c, int maxElements)
BlockingQueuec may result in elements being in neither,
either or both collections when the associated exception is
thrown. Attempts to drain a queue to itself result in
IllegalArgumentException. Further, the behavior of
this operation is undefined if the specified collection is
modified while the operation is in progress.drainTo in interface BlockingQueue<E>c - the collection to transfer elements intomaxElements - the maximum number of elements to transferUnsupportedOperationException - if addition of elements
is not supported by the specified collectionClassCastException - if the class of an element of this queue
prevents it from being added to the specified collectionNullPointerException - 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 Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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