Java provides two methods notify and notifyAll for waking up threads waiting on some condition and you can use any of them but there is a subtle difference between notify and notifyAll in Java. When you call notify only one of waiting for the thread will be woken and it's not guaranteed which thread will be woken, it depends on upon Thread scheduler. While if you call notifyAll method, all threads waiting on that lock will be woken up, but again all woken thread will fight for lock before executing remaining code and that's why wait is called on loop because if multiple threads are woken up, the thread which will get lock will first execute and it may reset waiting for condition, which will force subsequent threads to wait. So key difference between notify and notifyAll is that notify() will cause only one thread to wake up while notifyAll method will make all thread to wake up.
