Question

Why class is known as abstract data type?

Answer 1

Modern object-oriented languages, such as C++ and Java, support a form of abstract data types. When a class is used as a type, it is an abstract type that refers to a hidden representation. In this model an ADT is typically implemented as a class, and each instance of the ADT is usually an object of that class.

Answer 2

An abstract data type is a mathematical model where the data type is defined by  its behaviour. It is not an independent data type that can be handled universally. A class containing varoius objects implies a set of data members alomg with their operations to be performed. The handling of instance variables is done through member methods of a class . This is the reason why a class is known as an abstract data type.