Chapter 2: Java Object-Oriented Programming (OOP)

Object-Oriented Programming (OOP) was born out of the necessity for better control over the concurrent modification of shared data, which was the curse of pre-OOP programming. The core of the idea was not to allow direct access to data and instead, do it only through a dedicated layer of code. Since data needs to be passed around and modified in the process, the concept of an object was conceived. In the most general sense, an object is a set of data that can be passed around and accessed only through the set of methods passed along too. This data is said to compose an object state, while the methods constitute the object behavior. The object state is hidden (encapsulated) from direct access.

Each object is constructed based on a certain template called a class. In other words, a class defines a class of objects. Each object has a certain interface, a formal definition of the way other objects can interact with it. Originally, one...