What concept within object-oriented programming involves the restriction of the manipulation of an object's state by external users to a set of method calls?

The concept of data encapsulation within object-oriented programming involves the restriction of the manipulation of an object's state by external users.

Explanation:

In the discipline of object-oriented programming, objects are nothing else but repositories of data existing in the form of fields. Through data encapsulation, the vulnerable data is literally capsulated so that the object's state cannot be manipulated by any agent working externally. Hence, data encapsulation can be referred to as a secure procedure of safeguarding the objects (data repositories).