Explain wait(), notify() and notifyAll() methods in Java threading.

The Object class in Java has 3 final methods that allow threads to communicate about the locked status of a resource.

wait() instructs the calling thread to release the lock and go to sleep until some other thread enters the same monitor and calls notify(). The wait() method releases the lock prior to waiting and reacquires the lock prior to returning from the wait() method. It is a native method.

synchronized( monitorObj )
{ 
    while( ! condition )
    { 
        monitorObj.wait();
    }
     
    //critical section code
}

notify() wakes up one single thread that called wait() on the same object. It should be noted that calling notify() does not actually give up a lock on a resource. It tells a waiting thread that that thread can wake up.

synchronized(monitorObj) 
{
    //Condition to invoke notify
 
    monitorObj.notify();
     
    //additional code (optional)
}

notifyAll() wakes up all the threads that called wait() on the same object. The highest priority thread will run first in most of the situation, though not guaranteed.

synchronized(monitorObj) 
{
    //Condition to invoke notify
 
    monitorObj.notifyAll();
     
    //additional code (optional)
}

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