The threading methods are defined in Object class because these methods are related to object locks and any object can act as a lock and hence these methods are defined in the Object class. These methods are wait(), notify() and notifyAll(). These methods are final and return nothing. All of them must be called from a synchronized block or method and the thread calling them should pocess the lock on the object.
While calling wait() method, the thread to release the lock on Object on which wait() method is called and on calling the notify()/notifyAll() makes the other capture the lock.