1. Java Concurrency Utilities - java.util.concurrent
2. Java BlockingQueue
3. ArrayBlockingQueue
4. DelayQueue
5. LinkedBlockingQueue
6. PriorityBlockingQueue
7. SynchronousQueue
8. BlockingDeque
9. LinkedBlockingDeque
10. ConcurrentMap
11. ConcurrentNavigableMap
12. CountDownLatch
13. CyclicBarrier
14. Exchanger
15. Semaphore
16. Java ExecutorService
17. Java Callable
18. Java Future
19. ThreadPoolExecutor
20. ScheduledExecutorService
21. Java Fork and Join using ForkJoinPool
22. Java Lock
23. ReadWriteLock
24. AtomicBoolean
25. AtomicInteger
26. AtomicLong
27. AtomicReference
28. AtomicStampedReference
29. AtomicIntegerArray
30. AtomicLongArray
31. AtomicReferenceArray

The SynchronousQueue class implements the BlockingQueue interface. Read the BlockingQueue text for more information about the interface.

The SynchronousQueue is a queue that can be used to exchange a single element with another thread. A thread inserting an element into the queue is blocked until another thread takes that element from the queue. Likewise, if a thread tries to take an element and no element is currently present, that thread is blocked until a thread insert an element into the queue.

Calling this class a queue is a bit of an overstatement. It's more of a rendesvouz point.