Excerpt from old “Exploring Java” book.
It clearly states, what wait(), notify(), notifyAll() are used for and what they do.
With the synchronized keyword, we can serialize the execution of complete methods and blocks of code. The wait() and notify() methods of the Object class extend this capability. Every object in Java is a subclass of Object, so every object inherits these methods. By using wait() and notify(), a thread can give up its hold on a lock at an arbitrary point, and then wait for another thread to give it back before continuing. All of the coordinated activity still happens inside of synchronized blocks, and still only one thread is executing at a given time.
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