Statements (4) and (6) are correct. (4) is correct because the wait() method is overloaded to 

accept a wait duration in milliseconds. If the thread has not been notified by the time the wait 

duration has elapsed, then the thread will move back to runnable even without having been 

notified.

(6) is correct because wait()/notify()/notifyAll() must all be called from within a synchronized, 

context. A thread must own the lock on the object its invoking wait()/notify()/notifyAll() on.

(1) is incorrect because wait()/notify() will not prevent deadlock.

(2) is incorrect because a sleeping thread will return to runnable when it wakes up, but it might 

not necessarily resume execution right away. To resume executing, the newly awakened thread 

must still be moved from runnable to running by the scheduler.

(3) is incorrect because synchronization prevents two or more threads from accessing the same

 object.

(5) is incorrect because notify() is not overloaded to accept a duration.