Introduction to Object Oriented Programming Concepts

A Programming Language is a set of commands and syntax used to create a computer program. The various generations of programming languages are:

1. First Generation Programming Language — Machine language is the first-generation programming language (1GL). It is made up of binary number 0 (Zero) and 1 (One) so instructions in Machine language are sequences of zeros and ones. It is a low-level language.
2. Second Generation Programming Language — Assembly language is second-generation language (2GL). It uses symbolic operations called mnemonics instead of binary digits that can have up to maximum of five letters. Assembly language is also a low-level language.
3. Third Generation Programming Language — A third-generation language (3GL) is close to English in vocabulary. These languages are easier to read and require less time to write programs. Third-generation programming languages are high-level programming languages, such as FORTRAN, Java, C, and C++.
4. Fourth Generation Programming Language — A fourth-generation language (4GL) is closer to a natural language (for example, English) than a third- generation language. These languages are non-procedural. It means that the programmer specifies what is required as opposed to how it is to be done. Database languages such as Structured Query Language (SQL), report generators such as Oracle Reports, and Python are examples of fourth-generation languages.
5. Fifth Generation Programming Language — A fifth-generation language (5GL) is designed to solve a given problem using constraints given to the program, rather than using an algorithm written by a programmer. The fifth-generation languages are mainly used in Artificial Intelligence. Smalltalk, Prolog, and Mercury are good examples of the fifth-generation languages.

A programming paradigm is an approach or style of programming that is used to classify programming languages. Each programming language uses one or more programming paradigms. Two popular programming paradigms are:

1. Procedure Oriented Programming — In this programming paradigm, a complex programming problem is solved by dividing it into smaller problems using functions (or procedures).
2. Object Oriented Programming — In this programming paradigm, data and functions are wrapped into a single unit.

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.

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.

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.

From the viewpoint of the driver, a car is one single object. It can be operated using gears, indicators, accelerator, brake, etc. The driver doesn't need to know or understand the internal mechanisms of how these components actually work. From the viewpoint of the mechanic, it is important for him to understand how the internal mechanisms like gears, indicators, accelerator, brake, etc. actually work so that they can identify and fix issues with the cars. For a mechanic, each car part is a single object.

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.

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.

There are four principles of Object Oriented Programming:

1. Data Abstraction — It refers to the act of representing essential features without including the background details.
2. Encapsulation — It is a mechanism that binds the data and code (functions) together into a single unit.
3. Inheritance — It is a powerful mechanism by which one class acquires the properties of another class.
4. Polymorphism — It is the ability of a function or object to take on multiple forms.

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.