Object Oriented Programming Concepts

Object Oriented Programming (OOP) is a programming paradigm which revolves around the behaviour of an object, and its interactions with other objects and classes. In OOP, the program is organised around data or objects rather than functions or procedures. It follows the design principles of Data Abstraction, Encapsulation, Inheritance, and Polymorphism.

The world around us is made up of objects such as people, vehicles, buildings, streets, mobiles, television, etc. Each of these objects has the ability to perform specific actions and each of these actions influences the other objects in some way or the other. The objects around us can be divided into the following categories:

1. Tangible Objects — These are the objects that we can see and touch. For example, chair, pen, book, door, etc.

2. Conceptual Objects — These objects exists as a conceptual entity that we cannot touch. We may or may not be able to see them. For example, an email, a bank account, a song, patents, etc.

3. Roles — Roles played by people, such as a student, a teacher or a clerk.

4. Events — An event is something occurring in a system or an organisation. For example, a sale or a purchase in a departmental store, someone's birthday, etc.

The characteristics of object-oriented programming are:

1. It follows a bottom-up approach.
2. The program resulting from object-oriented programming is a collection of objects. Each object has its own data and a set of operations.
3. OOP restricts the free movement of data and the functions that operate on it.
4. A properly defined class can be reused, giving way to code reusability.
5. The concept of object-oriented programming models real-world entities very well.
6. Due to its object-oriented approach, it is extremely useful in solving complex problems.

Limitations of object-oriented programming:

1. The size of the programs created using this approach may become larger than the programs written using procedure-oriented programming approach.
2. Software developed using this approach requires a substantial amount of pre-work and planning.
3. OOP code is difficult to understand if you do not have the corresponding class documentation.
4. In certain scenarios, these programs can consume a large amount of memory.

Abstraction refers to the act of representing essential features without including the background details. For example, a building can be viewed as a single component (e.g., hospital) rather than separate components like cement, bricks, and rods. Abstraction is relative to the perspective of the viewer.

Encapsulation is a mechanism that binds together code and the data it manipulates. It keeps them both safe from the outside world, preventing any unauthorised access or misuse. Only member methods, which are wrapped inside the class, can access the data and other methods. For example, an ATM contains different denominations of currency notes and it provides a set operations to the user to withdraw money. The different denominations of currency notes is the data, the set of operations are the methods and the ATM encapsulates them into a single unit enabling us to withdraw cash conveniently.

The characteristics of procedural programming are:

1. Procedural programming follows a top-down approach.
2. The program is divided into blocks of codes called functions, where each function performs a specific task.
3. Procedural programs model real-world processes as 'procedures' operating on 'data'.
4. The data and functions are detached from each other.
5. The data moves freely in a program.
6. It is easy to follow the logic of a program.
7. A function can access other function's data by calling that function.

The limitations of procedural programming are:

1. Procedural programming mainly focuses on procedures or functions. Less attention is given to the data.
2. The data and functions are separate from each other.
3. Global data is freely moving and is shared among various functions. Thus, it becomes difficult for programmers to identify and fix issues in a program that originate due to incorrect data handling.
4. Changes in data types need to be carried out manually all over the program and in the functions using the same data type.
5. Limited and difficult code reusability.
6. It does not model real-world entities (e.g., car, table, bank account, loan) very well where we as a human being, perceive everything as an object.
7. The procedural programming approach does not work well for large and complex systems.

To explain Inheritance, let's take the example of traffic on the road. This traffic has some commonalities. It consists of things that can move on the road and transport people and goods from one place to another. We call these things vehicles. These vehicles differ from each other in certain aspects like whether it transports passengers or goods, how many passengers it can accommodate at a time, whether it is a two-wheeler or four-wheeler, etc. So, we have different types of vehicles like Cars, Bikes, Scooters, Auto rickshaw, Buses, Trucks, etc. We can represent this traffic using Inheritance as shown below. Here, Vehicle is the base class having the common characteristics and behaviours of all Vehicles. Then we have Car, Bike, Bus, Truck as subclasses of Vehicles.

Polymorphism is the ability of a method or an object to take on multiple forms. In OOP, polymorphism allows an operation to exhibit different behaviour in different instances. The behaviour depends upon the type of data used in the operation. For example, consider the operation of addition. For two numbers, the operation will generate a sum. If the operands are strings, then the operation would produce a third string by concatenation.

Encapsulation is a mechanism that binds together code and the data it manipulates whereas Inheritance is the mechanism by which a class acquires the properties and methods of another class. An ATM binding together the different denominations of currency notes and all the operations required to withdraw cash is an example of Encapsulation. Classifying Vehicles as Car, Bike, Bus, Truck, etc. is an example of Inheritance.

Objects are identifiable entities that have a set of attributes, behaviour and state. Five examples of objects are car, pen, mobile, email, bank account.

As class describes the common attributes and behaviours of its objects in detail, hence we can say that a class is a specification for objects. It can be viewed as a template or blueprint for multiple objects with similar features.

It means that there can be different abstractions of an entity depending on the viewpoint of the user. Lets take the example of a pet dog. From the viewpoint of the dog's owner, the things that are essential for the dog are his favorite food, the colour of his food bowl, his favorite game that he enjoys playing with his owner, his preferred time for walk, etc. From the viewpoint of the dog's vet (doctor for animals), the important things about the dog are whether the dog's body functions are normal or not to ensure that the dog is healthy. Like this, there can be two abstractions for the dog — one for the dog's owner and the other for the dog's vet.

ii. Teacher

iii. Laptop

iv. Radio

v. Table

vi. Telephone

vii. Dish Washer

viii. Microwave

ix. Aeroplane

x. Tree

xi. Cloud

The class is just a specification of the object. The attributes and methods in the class are thus declarations that do not contain any values. However, the object is a concrete instance of a class with properly defined values for each attribute and behaves as per the methods of the class.

A class is called an object factory because objects are created from the class that contains common attributes and behaviour. The class behaves like a specification for creating such similar objects.

ii. A composite data type

A class is composed of member variables which are of different data types. Hence, a class can be viewed as a composite data type.

iii. A user-defined data type

The entire data and the code, contained in an object, becomes a user-defined data type using the concept of a class. The class may be considered as a data type and an object as a variable of that data type. For example, once the Bird class has been defined, the statement
     Bird parrot;
will create a parrot object belonging to the Bird class.

A Class is used to create various Objects that have different attributes and common behaviours. Each object follows all the features defined within a class. That is why class is also referred to as a blue print or prototype of an object. For example, a class representing a car will have the following characteristics and behaviours:

We can create two objects of this class to represent a red i20 car and a white Baleno car as shown below:

An object stores its state in member variables and exposes its behaviour through the member methods. The member methods operate on member variables and serve as the primary mechanism to interact with the object. Only the member methods which are wrapped inside the class can access the data and change its state. Hence, the state and behaviour are said to be encapsulated by the object, hiding internal state and requiring all interaction to be performed through the methods of the object.

Objects communicate with each other by sending messages. The sender object requests the receiver object to perform an action.

ClassB is superclass and ClassA is subclass.

superclass is also known as base class and subclass is also known as derived class.

Student will be the superclass.