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.
extends
<E> | the type of elements held in this queue |