Why wait(), notify() and notifyAll() are in Object class

Question

As these methods will be used w.r.t threading. No mater how you create thread, you will create an object of Thread class or object of subclass of Thread class. Then why these methods are in Object and not in Thread class?

Answer 1

If all these methods present in Thread class, then if you are going to create a thread implementing Runnable interface, then this method is directly not available. If these methods are present in Runnable interface, then always we have to provide body for this. Thats why they kept these methods inside Object class.