Classes, Objects, and Design Explained with Practical Examples

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Classes, objects, and design — finally explained simply.

Many learners can write a class but aren't sure why it should exist, what belongs inside it, or how classes should work together. Encapsulation, polymorphism, composition, interfaces, SOLID, and design patterns sound intimidating, but each idea is simple once it is shown with real code. This book builds up one concept at a time with runnable Python, short Java/C#/TypeScript comparisons where they differ, and a realistic running example — then gives you exercises and worked solutions to make it stick.

• 632 pages · 28 chapters + 4 appendices
• Classes, objects, constructors, attributes, methods, and properties
• Encapsulation, abstraction, inheritance, and polymorphism — plus composition over inheritance
• Abstract classes, interfaces, protocols, special methods, and dataclasses
• Class diagrams, SOLID, cohesion and coupling, and the design patterns most worth knowing
• Testing, refactoring procedural code into objects, and OOP across Python, Java, C#, and TypeScript
• Exercises with worked solutions in every chapter
• Three complete projects, including a zoo management system

Table Of Contents

Part I — Thinking in Objects

• Ch 1 · Why Object-Oriented Programming? From Procedures to Objects
• Ch 2 · Objects and Classes: The Big Idea
• Ch 3 · Your First Class: Attributes, Methods, and init
• Ch 4 · Designing a Class: Responsibilities, State, and Behavior
• Ch 5 · Encapsulation: Protecting State with Methods and Properties

Part II — The Four Pillars and Beyond

• Ch 6 · Abstraction: Hiding Complexity Behind Simple Interfaces
• Ch 7 · Inheritance: Reusing and Extending Classes
• Ch 8 · Polymorphism: One Interface, Many Forms
• Ch 9 · Composition over Inheritance: Building Objects from Objects
• Ch 10 · Abstract Classes, Interfaces, and Protocols

Part III — Working with Objects

• Ch 11 · Special Methods: Making Objects Behave Like Built-ins
• Ch 12 · Class Attributes, Static Methods, and Class Methods
• Ch 13 · Objects Working Together: Relationships, Collections, and Associations
• Ch 14 · Identity, Equality, Copying, and Immutability (with dataclasses)
• Ch 15 · Exceptions in Object-Oriented Code: Custom Errors and Safe Objects

Part IV — Designing Good Object-Oriented Code

• Ch 16 · Class Diagrams and UML Made Simple
• Ch 17 · The SOLID Principles in Plain Language
• Ch 18 · Cohesion, Coupling, and Keeping Objects Independent
• Ch 19 · Design Patterns I: Creating Objects (Factory, Builder, Singleton)
• Ch 20 · Design Patterns II: Structural and Behavioral (Adapter, Decorator, Strategy, Observer, Command)

Part V — OOP in Practice

• Ch 21 · Testing Object-Oriented Code
• Ch 22 · Refactoring Procedural Code into Objects
• Ch 23 · OOP Across Languages: Python, Java, C#, and TypeScript Compared
• Ch 24 · Saving and Loading Objects: Files, JSON, and Databases
• Ch 25 · Common OOP Mistakes and How to Avoid Them

Part VI — Projects and Case Study

• Ch 26 · Project: A Text-Based Adventure Game with Objects
• Ch 27 · Project: A Shop Inventory and Ordering System
• Ch 28 · Case Study: Building the Mossgate Zoo Management System

Appendices

• App A · OOP Cheat Sheet
• App B · Class Design Templates and Pattern Reference
• App C · Object-Oriented Design Review Checklist
• App D · Glossary

WHO IT IS FOR
Beginners who know basic programming, students in programming or software-design courses, self-taught developers, and anyone moving between object-oriented languages.

FORMAT
PDF (A4), 632 pages, English, clickable table of contents and PDF bookmarks. 1st Edition, 2026. Published by thenexbooks.

Book details