Question

In oop which concepts allows class object to be used inside another class

Answer 1

Its loop where class is used inside another class.

Answer 2

In OOP ("Object Oriented Programming"), the concept which allows a class object to be used inside another class is instantiation.

In "Object Oriented Programming", the term instantiation is used to refer to the process of creation of an object which is also called as an instance of its class.

In "Object Oriented Programming", the classes have been defined as a prototype/ blueprint for the object whereas an object has been defined as an instance of the "class".