2.2 OOP Principles

Learning Objectives

•Name and briefly define the four core OOP principles.
•Recognize each principle in a small Java example.
•Explain why OOP improves maintainability over purely procedural code.

Introduction

Object-oriented programming rests on four pillars: encapsulation (bundling data with the methods that operate on it, hiding internal details), abstraction (exposing only what's necessary, hiding complexity), inheritance (reusing and extending behavior from a parent class), and polymorphism (treating different object types through a common interface). Chapter 2 focuses on encapsulation; Chapter 3 develops abstraction, inheritance, and polymorphism in depth.

Key Concepts

Encapsulation — bundling data with the behavior that manages it, and restricting direct outside access.

Abstraction — exposing only relevant details and hiding implementation complexity.

Inheritance — a class acquiring fields/methods from a parent class, enabling reuse.

Polymorphism — one interface, many implementations, letting different object types respond to the same call in their own way.

Common Mistakes

⚠Confusing encapsulation (hiding data) with abstraction (hiding complexity) — they're related but distinct.
⚠Treating OOP as "just adding classes" to procedural code, rather than actually designing around these four principles.

Practice

Practice 1

Multiple Choiceeasy

Which OOP principle is primarily about bundling data with the methods that operate on it, and restricting direct access?

Inheritance

Encapsulation

Polymorphism

Abstraction

Summary

OOP is built on encapsulation, abstraction, inheritance, and polymorphism. Chapter 2 focuses on encapsulation via classes and objects; Chapters 3–4 build on the rest.

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