Fundamental Object Oriented Programming (OOP) Concepts

OOP is a design philosophy. It stands for Object Oriented Programming. Object-Oriented Programming (OOP) uses a different set of programming languages than old procedural programming languages (C, Pascal, etc.). Everything in OOP is grouped as self sustainable "objects". Hence, you gain reusability by means of four main object-oriented programming concepts.

       In order to clearly understand the object orientation model, let’s take your “hand” as an example. The “hand” is a class. Your body has two objects of the type "hand", named "left hand" and "right hand". Their main functions are controlled or managed by a set of electrical signals sent through your shoulders (through an interface). So the shoulder is an interface that your body uses to interact with your hands. The hand is a well-architected class. The hand is being reused to create the left hand and the right hand by slightly changing the properties of it.

What is an Object?

An object can be considered a "thing" that can perform a set of related activities. The set of activities that the object performs defines the object's behavior. For example, the Hand (object) can grip something, or a Student (object) can give their name or address.

In pure OOP terms an object is an instance of a class.

What is a Class?

A class is simply a representation of a type of object. It is the blueprint, or plan, or template, that describes the details of an object. A class is the blueprint from which the individual objects are created. Class is composed of three things: a name, attributes, and operations.

In real world, you'll often find many individual objects all of the same kind. As an example, there may be thousands of other bicycles in existence, all of the same make and model. Each bicycle has built from the same blueprint. In object-oriented terms, we say that the bicycle is an instance of the class of objects known as bicycles.

In the software world, though you may not have realized it, you have already used classes. For example, the TextBox control, you always used, is made out of the TextBox class, which defines its appearance and capabilities. Each time you drag a TextBox control, you are actually creating a new instance of the TextBox class.

How to identify and design a Class?

This is an art; each designer uses different techniques to identify classes. However according to Object Oriented Design Principles, there are five principles that you must follow when design a class,

• SRP - The Single Responsibility Principle -
  A class should have one, and only one, reason to change.
• OCP - The Open Closed Principle -
  Should be able to extend any classes' behaviors, without modifying the classes..
• LSP - The Liskov Substitution Principle-
  Derived classes must be substitutable for their base classes.
• DIP - The Dependency Inversion Principle-
  Depend on abstractions, not on concretions.
• ISP - The Interface Segregation Principle-
  Make fine grained interfaces that are client specific.

Additionally to identify a class correctly, you need to identify the full list of leaf-level functions or operations of the system (granular level use cases of the system). Then you can proceed to group each function to form classes (classes will group same types of functions or operations). However a well-defined class must be a meaningful grouping of a set of functions and should support the reusability, while increasing expandability or maintainability, of the overall system.
In software world the concept of dividing and conquering is always recommended, if you start analyzing a full system at the start, you will find it harder to manage. So the better approach is to identify the module of the system first and then dig deep in to each module separately to seek out classes.
A software system may consist of many classes. When you have many classes, it needs to be managed. Think of a big organization, with its work force exceeding several thousand employees (let’s take one employee as one class). In order to manage such a work force, you need to have proper management policies in place. Same technique can be applied to manage classes of your software system. In order to manage the classes of a software system, and to reduce the complexity, system designers use several techniques, which can be grouped under four main concepts named

·         1. Encapsulation

·         2. Abstraction

·         3. Inheritance

·         4. Polymorphism.

·         These concepts are the four main gods of OOP world and in software term, they are called four main Object Oriented Programming (OOP) Concepts.

What is Encapsulation (or Information Hiding)?

The encapsulation is the inclusion-within a program object-of all the resources needed for the object to function, basically, the methods and the data. In OOP the encapsulation is mainly achieved by creating classes, the classes expose public methods and properties. A class is kind of a container or capsule or a cell, which encapsulate a set of methods, attribute and properties to provide its indented functionalities to other classes. In that sense, encapsulation also allows a class to change its internal implementation without hurting the overall functioning of the system.

What is Polymorphism?

Polymorphisms is a generic term that means 'many shapes'. More precisely Polymorphisms means the ability to request that the same operations be performed by a wide range of different types of things.
At times, I used to think that understanding Object Oriented Programming concepts have made it difficult since they have grouped under four main concepts, while each concept is closely related with one another. Hence one has to be extremely careful to correctly understand each concept separately, while understanding the way each related with other concepts.