OOP, SOLID & Design Patterns Practice

This repository demonstrates a structured, hands-on implementation of Object-Oriented Programming (OOP), SOLID principles, and common Design Patterns using a Hotel Management System (HMS) case study.

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📚 Course Reference

• 🎓 Course: https://www.udemy.com/course/oop-from-engineering-perspective/

• 👨‍🏫 Instructor: https://linkedin.com/in/sameh-muhammed-860570144/?skipRedirect=true

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🚀 Project Overview

The project starts with a structured (procedural) implementation and is progressively refactored into a clean object-oriented design.

The system includes:

• Room management
• Reservation system (Cancelable / Uncancellable)
• Meal ordering
• Checkout service

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🧠 Concepts Covered

OOP Principles

• Encapsulation
• Inheritance
• Abstraction
• Polymorphism

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SOLID Principles

• Single Responsibility Principle (SRP)
• Interface Segregation Principle (ISP)
• Dependency Inversion Principle (DIP)

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Design Patterns

• Factory Method
• Factory Pattern
• Builder Pattern
• Singleton Pattern
• Strategy Pattern (via composition)

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⚙️ Key Implementations

1. Inheritance & Polymorphism

• Room → SingleRoom, DoubleRoom, SweetRoom, TripleRoom
• Reservation → CancelableReservation, UncancellableReservation

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2. Abstraction & ISP

❌ Incorrect Design

DataAccessManager (fat interface)

✅ Correct Design

RoomDataAccessManager
MenuDataAccessManager

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3. Dependency Inversion (DIP)

• Business logic depends on interfaces instead of concrete implementations

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4. Builder Pattern

• RoomBuilder for flexible object creation

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5. Factory Pattern

• RoomFactory + RoomType for runtime object creation

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6. Singleton Pattern

• Hotel class ensures single instance

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7. Strategy Pattern (Composition)

• Implemented using IMovable in Bird example
• Demonstrates composition over inheritance

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8. Separation of Concerns

• Business Logic → management

• Data Access → interfaces

• Display Layer →

  • RoomDisplay
  • MenuDisplay
  • Console implementations

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9. Service Layer

• CheckoutService handles reservation checkout and room release

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📂 Project Structure

oop
 ├── model
 │   ├── room
 │   ├── reservation
 │   └── ...
 ├── management
 │   ├── abstraction
 │   │   ├── wrong
 │   │   └── correct
 ├── factory
 ├── builder
 ├── singleton
 ├── service
 └── util

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📌 Notes

• The project demonstrates gradual refactoring from procedural code to a maintainable OOP design.
• Each concept is applied incrementally and validated through commits.
• Focus is on design quality, not just functionality.

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🎓 Certificate

• https://www.udemy.com/certificate/UC-b015ebbd-2102-4446-8d28-22f3130f5f06/