Difference between wait() and sleep()

Question

What is the difference between a wait() and sleep() in Threads?

Is my understanding that a wait()-ing Thread is still in runni

Answer 1

There are some difference key notes i conclude after working on wait and sleep, first take a look on sample using wait() and sleep():

Example1: using wait() and sleep():

synchronized(HandObject) {
    while(isHandFree() == false) {
        /* Hand is still busy on happy coding or something else, please wait */
        HandObject.wait();
    }
}

/* Get lock ^^, It is my turn, take a cup beer now */
while (beerIsAvailable() == false) {
    /* Beer is still coming, not available, Hand still hold glass to get beer,
       don't release hand to perform other task */
    Thread.sleep(5000);
}

/* Enjoy my beer now ^^ */
drinkBeers();

/* I have drink enough, now hand can continue with other task: continue coding */
setHandFreeState(true);
synchronized(HandObject) {
    HandObject.notifyAll();
}

Let clarity some key notes:

1. Call on:
   • wait(): Call on current thread that hold HandObject Object
   • sleep(): Call on Thread execute task get beer (is class method so affect on current running thread)
2. Synchronized:
   • wait(): when synchronized multi thread access same Object (HandObject) (When need communication between more than one thread (thread execute coding, thread execute get beer) access on same object HandObject )
   • sleep(): when waiting condition to continue execute (Waiting beer available)
3. Hold lock:
   • wait(): release the lock for other object have chance to execute (HandObject is free, you can do other job)
   • sleep(): keep lock for at least t times (or until interrupt) (My job still not finish, i'm continue hold lock and waiting some condition to continue)
4. Wake-up condition:
   • wait(): until call notify(), notifyAll() from object
   • sleep(): until at least time expire or call interrupt
5. And the last point is use when as estani indicate:

you normally use sleep() for time-syncronization and wait() for multi-thread-synchronization.

Please correct me if i'm wrong.