Topic about wait(),join(),sleep() and yield()

Question

Hi there,
I'm headache with the implementation of wait()��join()�� sleep() yield(). Can anybody tell me:
1. what's the difference between wait() and join(), I can't see it.
2. As I know if thread A waits on thread B then A will release the lock. How about join, or slepp, or yield?
3. Why use notify()? As I see if thread A waits on thread B, when B completed without calling notify(), the A will continue its job!!
thanks thanks thanks

Answer 1

1. Object.wait() will make a thread wait until Object.notify() is called on the object. Thread.join() will make the running thread to wait until the thread object finish to execute.
2. .wait() does not wait on thread, it wait on objects. .sleep(long timeout) is about the same as .wait(long timeout), except that it need to be awaken with a .interrupt, not .notify. Also you cannot awaken more than one thread with a .interrupt, while a call to .notifyAll() will awaken all threads waiting on that object. .yield() suspend the current thread only to give a chance to others thread to execute and the initial thread will continue ot execute only a hort time after the .yield().
3. See #1, #2 and think a bit.
Regards