Difference between wait() and sleep()

Question

Is there any difference between a wait() and sleep() in Threads?

I know that a wait()-ing Thread is still in running mode and uses CPU cycles but a sleep()-ing does not use any CPU cycles, right?

Then why do we have both wait() and sleep() and how does their implementation change at a lower level?

Answer 1

The difference between sleep() and wait() is:

	Wait()	Sleep()
A method called on	Call on an object; the current thread must synchronize on the lock object.	Call on a Thread; always currently executing the thread.
Synchronized	when synchronized multiple threads access the same Object one by one	when synchronized multiple threads wait for sleepover of sleeping thread
Lock duration	release the lock for other objects to have a chance to execute	keep lock for at least t times if timeout specified or somebody interrupts
wake up condition	until call notify(), notifyAll() from object	until at least time terminate or call interrupt()
Usage	for time-synchronization	for multi-thread-synchronization
Example	synchronized(LOCK) {       LOCK.wait(); // LOCK is not held }	synchronized(LOCK) {       Thread.sleep(1000); // LOCK is held }