Introduction to Object Orientation

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

// 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