OOP refers to a software programming approach that uses objects defined as classes. These definitions include fields, sometimes called attributes, to store data and methods in order to provide functionality. The first OOP language was a simulation of real systems known as Simula (https://en.wikipedia.org/wiki/Simula) and was developed at the Norwegian Computing Center in 1960. The first pure OOP language came into existence in 1970 as the Smalltalk (https://en.wikipedia.org/wiki/Smalltalk) language. This language was designed to program the Dynabook (http://history-computer.com/ModernComputer/Personal/Dynabook.html), which is a personal computer created by Alan Kay. Several OOP languages evolved from there, with the most popular being Java, C++, Python, and C#. 

With the use of the OOP approach, we are doing the following:

• Modularizing: Here, an application is decomposed into different modules.
• Reusing the software: Here, we rebuild or compose an application from different (that is, existing or new) modules.

In the following sections, we will discuss and understand the concepts of OOP in more detail.