Object-Oriented Programming (OOP in short form) is a programming pattern that has gained very high popularity in the recent years. If we have to explain OOP in one line, then it could be – OOP is based on the idea of creating objects, which are instances of classes that encapsulate data & behavior and interact with each other through well-defined interfaces.

It is a powerful and flexible way to design and organize code. It has become a go-to approach for building simple as well as complex software systems. By using OOP concepts, a developer can write more maintainable, reusable, and scalable code by focusing on the behavior of object rather than implementation details. Whether you’re a seasoned developer or just starting out, understanding OOP is essential to master modern software development. So, in this post, we’ll explore the key concepts and principles of OOP along with its benefit and criticism.

Object-Oriented Programming

Structure of Object-Oriented Programming

In Object-oriented programming, the main focus remains on the objects for which we will manipulate data/methods instead of implementation of the same. To understand the OOP, we need to understand the structure of OOP. Let us take an example code to understand the structure in detail. Below is a C++ code of a class that represents Bank Account.

OOP example

In this above example, BankAccount is a class that has attributes (balance, accountHolderName, bankAccountNumber) and three methods (deposit, withdraw, and get_balance). Here, an object is an instance of the BankAccount class. We can create multiple objects of the same class (i.e. BankAccount), each with their own unique data values for the attributes defined in the class. So, an application can use the BankAccount class as an object for every customer to hold respective attributes. Now let us understand these terms in detail.


In Object-Oriented Programming, an object is an instance of a class. When we create an object of a class, we are creating a variable of that class type. So, it will not be wrong to say that an object is a variable of a class type. The object has its own set of attributes, which can be accessed and modified using the methods defined in the class.

Whenever we start OOPs programming then we should consider thinking the object as a real-world object. It is possible that these objects can be some real objects just like car, phone, dog, cat, or it can be something that cannot be seen/touched such as bank account, events etc.

In the above example of a BankAccount, each object of the BankAccount class represents a bank account with a unique account balance, account holder’s name and account number.


A class is a blueprint or template for creating objects. A class defines the attributes and behavior of the objects that it creates.

In the BankAccount example, a BankAccount class defines the blueprint to create bank account objects. The class specifies the attributes of a bank account object, which in this case is the account balance, bank holder name and the bank account number. The class also specifies the behavior of a bank account object, which includes the ability to deposit and withdraw money, and to retrieve the current account balance.


In Object-Oriented Programming, an attribute (also called a data member or instance variable) is a piece of data that belongs to an object. An attribute defines the state of an object and represent the characteristics or the properties of an object.

If we talk about car, then its color, speed, horsepower etc., are its attributes. When we talk about dog then its color, weight, height etc., are its attributes. In our example of BankAccount, the bank balance, account holder name, account number are attributes.


A method (also called a member function) is a block of code that belongs to a class and operates on objects of that class. Methods are used to perform operations on the object’s attributes, and it can modify the state of the object. In simple terms we can say that methods are the functions of the class that are used to describe the behavior of class.

In our BankAccount example, the deposit, withdraw, and get_balance functions are the methods of the BankAccount class. These methods define the behavior of a bank account object and allow us to interact with the BankAccount object by performing operations on it.

I hope you have now better clarity about the structure of the Object-Oriented programming. Please make it very clear before moving ahead as we will be using these for rest of the discussion. If you have any doubt, then please feel free to drop the comments on this page.

Principle of Object-Oriented Programming

There are four fundamental principles of Object-Oriented programming. These are also known as the four pillars of OOP. These four pillars of OOP provide a way to write code that is modular, reusable, and easy to maintain. These principles are also foundation for many design patterns and best practices in modern software engineering. Let us discuss each of it in detail.


In OOP, abstraction is about focusing on the essential properties and behaviors of an object and at the same time ignoring the details that are not relevant to its use.

Let’s understand it using our bank account example. From outside the class/instance, we don’t need to know how the BankAccount class actually manages its balance, how and where it stores the balance. We also don’t know the format of the balance; we don’t know how it is calculated or what kind of data structure is used for its operations. And the reality is that we don’t need to know this information. We only need to know that we can deposit the money & withdraw the money from the bank account. We know that the balance will be updated accordingly so there is no need to worry about its implementation.

So, by abstracting away these implementation details, we can create a simpler, more intuitive interface for working with the BankAccount class. We can think of the balance as a single value that can be increased or decreased, without worrying about how it’s actually managed behind the scenes.

Abstraction is important because it allows us to create more flexible and adaptable code. By focusing on the essential properties and behaviors of an object, we can create code that is more reusable and easier to modify over a period of time. If we need to change the way that the BankAccount class manages its balance, for instance, we can do so without affecting the way that other parts of the program interact with the class. This makes it easier to maintain and extend our code over time, and allows us to build larger, more complex systems that are easier to work with and more important its easier understand & maintain the code.


Encapsulation in object-oriented programming is about bundling the related data and the behaviors (i.e. methods) into a single unit (i.e., class) and hiding the details of how that class works from the outside world.

By hiding the implementation details of a class, encapsulation allows us to change the way a class works without affecting the code that uses it. By using encapsulation, we make the code easier to maintain and modify over a period of time. This happens because of the changes to the implementation of a class doesn’t affect the way that the other parts of the program use it.

Encapsulation also provides a way to ensure that the data and behaviors of a class is used in a consistent and predictable way. By restricting access to the data and behaviors of the class, we can prevent the accidental changes or misuse of that class and on the other hand we ensure that it always behaves in the way it is supposed to.

For example, in the bank account example I gave earlier, the balance attribute of the BankAccount class is declared as private, which means that it can only be accessed and modified from within the class itself. This ensures that the balance is always managed in a consistent and reliable way, and prevents accidental changes to the balance that could cause errors or inconsistencies in the program.


Inheritance in object-oriented programming is about creating new classes that are based on existing classes, and that it inherits their attributes and behaviors just like how we human beings inherit many things from our parents, grandparents, grand grandparents.

When a class inherits from another class, it automatically gains all of the properties and methods of the parent class. This allows us to create new classes that are similar to existing ones but with some differences or additions.

Lets understand it with our classic BankAccount example. Let us create a Savings Account class that inherits from our BankAccount class. This SavingsAccount class will have all the properties and methods that the BankAccount class have. But it will have some additional behavior that are specific to the savings accounts such as interest calculations.

OOP Inheritance example

In this example, the SavingsAccount class inherits from the BankAccount class using the public keyword. This means that all of the public methods of the BankAccount class (including deposit, withdraw, and get_balance) are inherited by the SavingsAccount class and it will be able to use them directly.

The SavingsAccount class also has its own private rate attribute and a add_interest method that calculates and deposits interest into the savings account.

Note: In the constructor of the SavingsAccount class, we call the constructor of the BankAccount class using the : notation. This initializes the balance attribute of the BankAccount class with the given initial_balance value. By using inheritance in this way, we don’t need to duplicate the code for managing the balance in both the BankAccount and SavingsAccount classes. We have simply reused the existing code from the parent class. [This also makes the lazy programmers happy as they don’t have to write code again :D]


Polymorphism is a principle that allows objects of different classes to be treated as if they were objects of the same class.

In simpler terms, polymorphism allows us to use a single interface to represent multiple different types of objects. This means that we can write code that works with a generic type of object, and then later substitute different specific types of objects without needing to change the code.

In the context of our bank account, polymorphism might mean that different types of bank accounts (such as current accounts, savings accounts, or credit card accounts) can have the same methods but those will behave differently depending on the specific implementation of those methods.

For example, Lets add a function i.e. method named print_balance which will print the balance of the bank account. In a current account, this method will print the balance as a dollar amount upto two decimal places, while in a savings account, it might print the balance in INR along with the interest rate and the projected balance after interest is added to it.

Polymorphism allows us to write generic code that can be used with multiple types of bank accounts, without needing to know the specific implementation details of each account type.

In C++, polymorphism can be achieved through the use of virtual functions and function overriding (We will discuss both of these in some other post in detail). By declaring a function as virtual in a parent class, we can override that function in child classes with their own implementation. This allows objects of the child class to use their own implementation of the function, instead of using the implementation from the parent class.

Here’s an example of how polymorphism might be used in a bank account system:

OOP Polymorphism example

In this example, when we are calling the print_balance method on a CurrentAccount or SavingsAccount object then the respective print_balance will be called. This will allow us to write generic code that works with different types of bank accounts and produces different output depending on the specific type of the account.

Design Patterns

Object-oriented programming concepts such as inheritance, polymorphism, encapsulation, and abstraction are very important in creating good design patterns. Design patterns use these concepts to provide a general solution to a recurring problem in software design.

There are many types of design patterns. I highly recommend you reading Design Patterns post which explain them in very detail. Creational patterns focus on object creation mechanisms, trying to create objects in a manner suitable to the situation. Structural patterns focus on object composition, creating relationships between objects to form larger structures. Behavioral patterns focus on communication between objects, defining how objects interact with each other to perform a task.

Some common design patterns that use OOP concepts include the factory method pattern, singleton pattern, observer pattern etc. Each of these patterns uses OOP concepts in a unique way to solve a specific design problem. By understanding and applying these patterns, you can improve the quality, maintainability, and extensibility of your software designs.


There are several benefits to using object-oriented programming (OOP) in software development. Here are some of the key advantages:

Reusability: OOP allows you to reuse code by creating objects that can be used in different parts of your application. This can save time and effort in development, as you don’t need to rewrite the same code multiple times.

Modularity: OOP promotes modularity in software design, allowing you to break down complex systems into smaller, more manageable components. This makes it easier to maintain, debug, and update your code.

Productivity: OOP can increase productivity as it enables developers to reuse code, write modular code, and focus on the essential features of an object. This means that developers can write code more quickly and with fewer errors.

Maintainability: OOP promotes modularity and encapsulation, which makes code easier to maintain. Changes can be made to specific parts of the code without affecting the entire program. Additionally, OOP’s inheritance feature allows for the reuse of code, which makes maintaining a program much easier.

Security: OOP provides encapsulation, which means that data and methods are hidden from other parts of the program. This improves security and reduces the risk of bugs and errors. Additionally, OOP’s inheritance feature allows for the reuse of code, which can reduce the risk of security vulnerabilities caused by writing new code.

Flexibility: OOP supports polymorphism, which means that different objects can respond to the same method in different ways. This enables you to write more flexible and adaptable code that can handle a variety of situations. Additionally, OOP’s inheritance feature allows for the creation of new classes based on existing ones, which makes it easier to reuse code and build on existing functionality.

Ease of understanding: OOP promotes abstraction, which means that you focus on the essential features of an object and ignore the non-essential details. This helps to create simpler and more manageable code that is easier to understand. Additionally, OOP’s encapsulation feature means that data and methods are hidden from other parts of the program, making it easier to understand the functionality of different parts of the code.


While OOP has many benefits in one hand, but it has criticisms also in other hand. Some critics argue that OOP is too complex, leading to unnecessarily large and convoluted code. Additionally, OOP can be difficult to learn for new developers, who may struggle to understand the complex relationships between classes and objects.

Another criticism of OOP is that it can be less efficient than other programming patterns. Because OOP relies heavily on inheritance and polymorphism, it can require more memory and processing power than other approaches. Additionally, OOP can be more difficult to optimize, as small changes to one part of the code can have unintended consequences on other parts of the program.

Some critics argue that OOP can lead to a lack of flexibility and adaptability. Because OOP relies on creating classes and objects that are tightly coupled to one another, it can be difficult to make changes to one part of the code without affecting the entire program. This can be especially problematic in large, complex programs, where even small changes can have wide-ranging effects. Additionally, OOP can make it difficult to create new functionality or adapt to new requirements, as doing so often requires creating entirely new classes and objects.

Rob Pike, a programmer who was part of UTF-8 and Go, has called object-oriented programming “the Roman numerals of computing“. In a blog post has said that OOP languages frequently shift the focus from data structures and algorithms to types.


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