Object-Oriented Programming Explained: Classes, Objects and the Four Pillars

Object-oriented programming (OOP) is a software design approach that organises code into self-contained units called objects, each combining related data and behaviour. Built on four pillars — encapsulation, inheritance, polymorphism and abstraction — OOP makes large codebases easier to maintain, extend and debug. Java, Python, C++ and C# all support it as a core pattern.

Instead of writing one long sequence of instructions, you model your program around things that mirror the real world. OOP makes large codebases easier to maintain, extend and debug, which is why it sits at the heart of Java, C++, Python and most enterprise software built today.

• A class is a blueprint; an object is a live instance created from that blueprint.
• OOP is built on four pillars: encapsulation, inheritance, polymorphism and abstraction.
• Java, C++, Python and C# are object-oriented languages. Plain C is not.
• OOP solves a real maintenance problem: procedural code breaks apart as codebases grow past a few thousand lines.
• OOP is not perfect. For some problems, composition and functional patterns work better.

What Is Object-Oriented Programming and the Problem It Solves

Imagine a team of 30 engineers at an Indian fintech startup all editing the same 10,000-line script. One person changes a variable name, and three unrelated features break overnight. This is the classic maintenance nightmare that object-oriented programming was designed to prevent.

In procedural programming, you write a top-to-bottom list of instructions. Functions operate on shared data, and as the program grows, the connections between those functions become tangled. C is the most widely known procedural language, and it works brilliantly for operating systems and embedded code where fine control matters. But it does not give you built-in tools to bundle data with the functions that act on it.

Object-oriented programming fixes this by organising code around objects. Each object owns its own data and exposes a clean interface to the rest of the program. When something breaks, you know exactly which object to look at. The concept was formalised in the 1960s with Simula, popularised by Smalltalk in the 1970s, and then carried into mainstream software through C++ and Java in the 1980s and 1990s.

According to the Stack Overflow Developer Survey 2024, JavaScript, Python and Java remain three of the top five most-used languages globally, and all three support object-oriented design as a first-class pattern. That is not a coincidence; it reflects how central OOP is to real-world development work.

What Is a Class in Programming?

A class is a template or blueprint that defines what data an object will hold and what actions it can perform. Think of a class called BankAccount. The class defines that every bank account has an owner name, a balance and methods like deposit() and withdraw().

The class itself does not hold any real money. It is just the design document.

What Is an Object in Programming?

An object is a specific, live instance of a class. When a customer opens an account at SBI, the bank’s software creates a new BankAccount object for that customer. That object has a real balance, a real owner name and can actually process transactions. You can create thousands of objects from one class, each with its own state.

The crisp distinction: the class is the cookie cutter, the object is the cookie.

The Four Pillars of Object-Oriented Programming with Real Examples

Every textbook lists the four pillars, but they make more sense when you follow a single model through all four. We will use a BankAccount throughout.

Encapsulation: Hiding Internal Data

Encapsulation means hiding the internal details of an object and exposing only what other parts of the program need. The balance field in a BankAccount object should not be directly editable by outside code. Instead, you expose a deposit() method that validates the amount before touching the balance.

The benefit: you can change how the balance is stored internally without breaking every other part of the program that calls deposit(). This is the foundation of the SOLID principles, specifically the open/closed principle that experienced engineers care about deeply.

Inheritance: Reusing Code Across Classes

Inheritance lets one class acquire the properties and methods of another. A SavingsAccount class can inherit from BankAccount, automatically getting the owner, balance and transaction methods, then add its own calculateInterest() method on top.

You write common logic once and reuse it across many specialised classes. This is a big reason why Java is considered an object-oriented programming language at its core; Java’s entire standard library is built as a hierarchy of inheriting classes.

Polymorphism: One Method Name, Many Behaviours

Polymorphism means the same method name can behave differently depending on the object that calls it. A CurrentAccount and a SavingsAccount both have a calculateInterest() method, but each computes it differently. Your billing system can call calculateInterest() on any account type without needing to know which type it is dealing with.

The benefit is flexibility. You can add a new account type later without touching the billing code at all.

Abstraction: Exposing Only What Is Necessary

Abstraction means exposing only the essential features of an object and hiding the complexity underneath. When a teller clicks “Process Transfer” in a bank application, they do not see database queries, encryption routines or network calls. They see one simple action.

In code, abstraction is implemented through abstract classes and interfaces. You define what an object must do without specifying how it does it. This keeps interfaces clean and makes swapping implementations straightforward.

Limitations of OOP: When to Use Composition Instead

Object-oriented programming is powerful, but it is not always the right tool. Deep inheritance chains become brittle and hard to reason about. Many experienced engineers now prefer composition over inheritance, building objects by combining small, focused behaviours rather than creating tall class hierarchies. Functional programming languages like Haskell, and even modern Python and JavaScript code, often avoid classical OOP for this reason. Knowing OOP well means knowing when not to use it too.

Which Languages Are Object-Oriented Programming Languages?

The phrase “object-oriented programming language” means the language provides built-in syntax for defining classes, creating objects and implementing the four pillars. Not every language does this, and some do it partially.

Language	Object-Oriented?	Notes
Java	Yes (strongly)	Almost everything is a class; used in Android and enterprise systems
C++	Yes (multi-paradigm)	Adds OOP on top of C; used in game engines and system software
Python	Yes (multi-paradigm)	Supports OOP but does not enforce it; very popular in data science and AI
C#	Yes (strongly)	Microsoft’s answer to Java; dominant in .NET and Unity game development
C	No	Purely procedural; no class syntax, no inheritance, no polymorphism
JavaScript	Partially	Prototype-based OOP; ES6 added class syntax as a cleaner layer
Haskell	No	Functional language; uses type classes, not OOP classes

Why Java Is an Object-Oriented Programming Language

Java was designed from day one to be object-oriented. Every piece of Java code, apart from a small set of primitive types like int and boolean, lives inside a class. You cannot write a standalone function in Java the way you can in C. This enforced structure is why Java became the dominant language for large enterprise applications and why it is the language taught in most Indian engineering colleges under the subject “Object-Oriented Programming with Java.”

The TIOBE Index for June 2025 ranks Java as the second most popular programming language globally, behind Python. Its staying power comes directly from the maintainability that OOP gives large teams.

Is C an Object-Oriented Programming Language?

No. C is a procedural language. It has no class keyword, no inheritance mechanism and no built-in way to bundle data with functions. You can simulate some OOP-like patterns in C using structs and function pointers, but the language does not enforce or support the four pillars natively. C++ was created specifically to add OOP capabilities to C while keeping its performance characteristics.

If you are exploring programming languages for emerging tech like blockchain or Web3 contracts, check out our guide on top programming languages for blockchain developers to see how OOP-based languages fit into that space.

OOP vs Procedural Programming: A Practical Comparison

In a procedural approach, you would write separate functions like getBalance(accountId), deposit(accountId, amount) and withdraw(accountId, amount), all operating on shared data structures. When you need to add a new account type, you modify existing functions and risk breaking things that already work.

In an object-oriented programming approach, you create a BankAccount class, then subclass it. Existing code does not change. According to a NIST report on software quality and maintainability (2022), structured design approaches including object-oriented programming reduce long-term defect rates and maintenance overhead significantly compared to unstructured procedural codebases of equivalent size.

India’s IT sector, which employs over 5.4 million software professionals according to NASSCOM’s Technology Sector Report 2024, relies heavily on Java and Python-based object-oriented programming across service delivery, banking software and enterprise platforms at firms including TCS, Infosys and Wipro. Students at IITs, NITs and private engineering colleges across India typically encounter OOP in their second-year programming courses.

If you want structured, project-based practice beyond the classroom, 3.0 University’s bootcamp training programs give you hands-on experience building real systems from scratch.

Getting peer support while you learn makes a measurable difference. The REACH learner community at 3.0 University connects you with other students and working professionals who are going through the same learning curve.

The GitHub Student Developer Pack, which bundles tools useful for OOP projects, has expanded its benefits for Indian students. You can read the full breakdown in our Learn: GitHub Education program update.

Object-oriented programming is one piece of a much larger picture. For deeper dives into programming, AI, cybersecurity and career strategy, the 3.0 University blog publishes practical guides written for learners at every stage.

If you are ready to move from concepts to credentials, 3.0 University’s online certification courses cover Cybersecurity, Ethical Hacking, AI, Blockchain and Web3, all built around labs and real-world projects that employers actually recognise. Whether you are a fresh graduate, a working professional switching tracks or a student who wants to get ahead, these courses are designed to give you skills you can demonstrate on day one of a job.

Frequently Asked Questions

What is object-oriented programming?

Object-oriented programming is a software design approach that organises code into objects, each combining related data and behaviour. Instead of writing long procedural scripts, you model your program around real-world entities like users, accounts or products. OOP makes code reusable, easier to maintain and simpler to extend as requirements change over time.

What are the four pillars of OOP?

The four pillars are encapsulation, inheritance, polymorphism and abstraction. Encapsulation hides internal data. Inheritance lets classes reuse code from parent classes. Polymorphism allows the same method to behave differently across object types. Abstraction exposes only what is necessary and hides complexity. Together, they help you write cleaner, more maintainable software.

What is the difference between a class and an object?

A class is a blueprint or template that defines structure and behaviour. An object is a specific, live instance created from that blueprint. For example, BankAccount is a class. The account belonging to a particular customer is an object. One class can produce thousands of objects, each holding its own unique data.

Which languages are object-oriented programming languages?

Java, C++, Python, C# and Ruby are the most widely used object-oriented programming languages. Java and C# enforce OOP strictly. Python and C++ support it alongside other paradigms. JavaScript uses prototype-based OOP with a class syntax layer added in ES6. C is procedural and not object-oriented.

Is C an object-oriented programming language?

No, C is a procedural language. It has no class syntax, no inheritance and no built-in polymorphism. You can mimic some OOP patterns using structs and function pointers, but the language does not support OOP natively. C++ was created to extend C with full object-oriented capabilities while keeping its low-level performance.

What is the difference between OOP and procedural programming?

Procedural programming organises code as a sequence of functions operating on shared data. Object-oriented programming bundles data and functions together inside objects. OOP makes it easier to add new features without breaking existing code, which is why it scales better for large teams and complex applications.

Last updated: June 2025. Reviewed by the 3University editorial team.