Yes, you can call private method in another class even you don´t need to extend it. You can do it by reflection API. Following link describes very well explained example of calling private method in another class.
Example of Calling Private Method in another class
We declare the method as private due to some reason. and private method can not be called in child class normally as we call default or public methods. If you want to restrict any method to be accessed in another class, You can use protected in place of private.
