Earlier, programming approaches had limitations and they often became difficult to maintain. OOP offered a new paradigm in software development that had advantages over other approaches. The concept of organizing code into objects is not difficult to explain and this is a huge advantage for the adoption of a new pattern. Many examples can be taken from the real world in order to explain the concept. Complex systems can also be described using smaller building blocks (that is, an objects). These allow developers to look at sections of the solution individually while understanding how they fit into the entire solution.
With this in mind, let's define a program as follows:
As you can see, an object is a way of organizing a list of instructions in a logical manner. Going back to the example of the house, the architect's instructions help us to build a house, but they are not the house itself. Instead the architect's instructions are an abstract representation of a house. A class is similar as it defines the features of an object. An object is then created from the definition of a class. This is often called instantiating the object.
To understand OOP more closely, we should mention two other significant programming approaches:
- Structured programming: This is a term coined by Edsger W. Dijkstra in 1966. Structured programming is a programming paradigm that solves a problem to handle 1,000 lines of code and divides these into small parts. These small parts are mostly called subroutines, block structures, for and while loops, and more. Languages that use structured programming techniques include ALGOL, Pascal, PL/I, and more.
- Procedural programming: This is a paradigm derived from structured programming and is simply based on how we make a call (also known as a procedural call). Languages that use procedural programming techniques include COBOL, Pascal, and C. A recent example of the Go programming language was published in 2009.
A procedural call is where a collection of statements, known as a procedure, is activated. This is sometimes referred to as a procedure that is invoked.
The main problem with these two approaches is that programs are not easily manageable once they grow. Programs with more complex and larger code bases strain these two approaches, leading to difficult-to-understand and difficult-to-maintain applications. To overcome such problems, OOP provides the following features:
- Inheritance
- Encapsulation
- Polymorphism
In the following sections, we will discuss these features in more detail.
Before we begin, let's discuss some structures that are found in OOP.