E - the type of elements held in this collection
public 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
Always returns
false.
|
boolean |
containsAll(Collection
Returns
false unless the given collection is empty.
|
int |
drainTo(Collection
Removes all available elements from this queue and adds them to the given collection.
|
int |
drainTo(Collection
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 |
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
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
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
Always returns
false.
|
boolean |
removeAll(Collection
Always returns
false.
|
boolean |
retainAll(Collection
Always returns
false.
|
int |
size()
Always returns zero.
|
Spliterator |
spliterator()
Returns an empty spliterator in which calls to
Spliterator 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 add
InterruptedException - if interrupted while waiting
NullPointerException - if the specified element is null
public boolean offer(E e, long timeout, TimeUnitunit) throws InterruptedException
offer in interface
BlockingQueue<E>
e - the element to add
timeout - how long to wait before giving up, in units of
unit
unit - a
TimeUnit determining how to interpret the
timeout parameter
true if successful, or
false if the specified waiting time elapses before a consumer appears
InterruptedException - if interrupted while waiting
NullPointerException - if the specified element is null
public boolean offer(E e)
offer in interface
BlockingQueue<E>
offer in interface
Queue<E>
e - the element to add
true if the element was added to this queue, else
false
NullPointerException - if the specified element is null
public E take() throws InterruptedException
take in interface
BlockingQueue<E>
InterruptedException - if interrupted while waiting
public E poll(long timeout, TimeUnitunit) throws InterruptedException
poll in interface
BlockingQueue<E>
timeout - how long to wait before giving up, in units of
unit
unit - a
TimeUnit determining how to interpret the
timeout parameter
null if the specified waiting time elapses before an element is present
InterruptedException - if interrupted while waiting
public E poll()
public boolean isEmpty()
true. A
SynchronousQueue has no internal capacity.
isEmpty in interface
Collection<E>
isEmpty in class
AbstractCollection<E>
true
public 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.
public boolean contains(Objecto)
false. A
SynchronousQueue has no internal capacity.
contains in interface
Collection<E>
contains in interface
BlockingQueue<E>
contains in class
AbstractCollection<E>
o - the element
false
public boolean remove(Objecto)
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 remove
false
public 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 collection
false unless given collection is empty
AbstractCollection.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 collection
false
AbstractCollection.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 collection
false
AbstractCollection.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 collection
a - the array
NullPointerException - if the specified array is null
public int drainTo(Collection<? super E> c)
BlockingQueue
c 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 into
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
public int drainTo(Collection<? super E> c, int maxElements)
BlockingQueue
c 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 into
maxElements - the maximum number of elements to transfer
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