---
title: "Introduction to Object Orientation"
description: The software crisis, OOP advantages, core concepts, and the four pillars of OOP.
---
## The Software Crisis

As software systems grew in complexity, procedural programming struggled with maintainability, scalability, and reuse. Object-Oriented Programming (OOP) emerged as a paradigm to address these challenges.

## OOP Advantages

- **Modularity** — Code is organized into self-contained objects.
- **Reusability** — Classes can be reused across projects.
- **Extensibility** — New functionality can be added through inheritance.
- **Maintainability** — Encapsulated code is easier to debug and update.

## Core OOP Concepts

- **Objects** — Instances of classes that hold state (attributes) and behavior (methods).
- **Classes** — Blueprints that define the structure and behavior of objects.
- **Instantiation** — The process of creating an object from a class using the `new` keyword.

## Attributes and Methods

- **Instance variables** — Data held by each object.
- **Methods** — Functions defined inside a class that operate on instance data.

## Four Pillars of OOP

1. **Encapsulation** — Bundling data and methods, restricting direct access.
2. **Inheritance** — Deriving new classes from existing ones.
3. **Polymorphism** — Same interface, different implementations.
4. **Abstraction** — Hiding implementation details, exposing only essentials.

## Example

```java
// OOPConcepts.java
// Demonstrates basic OOP concepts: class, object, and method.

// Class definition
class Dog {
	// Attribute (instance variable)
	String name;

	// Method definition
	void bark() {
		// Print dog's name and bark
		System.out.println(name + " says Woof!");
	}
}

public class OOPConcepts {
	public static void main(String[] args) {
		// Create Dog object
		Dog d = new Dog();
		d.name = "Buddy"; // Set name
		d.bark(); // Call method
	}
}
```

> Full source: [`examples/04-oop-intro/OOPConcepts.java`](https://github.com/University-Of-Sri-Jayewardenepura/Java/blob/main/examples/04-oop-intro/OOPConcepts.java)