Design Principles – SOLID (Java)

This repository is a hands-on implementation of SOLID design principles in Java, starting with the Single Responsibility Principle (SRP).

The goal of this project is to build practical, clean examples for all five SOLID principles with simple and understandable code.

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📌 What Are SOLID Principles?

SOLID is a set of five object-oriented design principles:

• S – Single Responsibility Principle (SRP)
• O – Open/Closed Principle (OCP)
• L – Liskov Substitution Principle (LSP)
• I – Interface Segregation Principle (ISP)
• D – Dependency Inversion Principle (DIP)

This repository will contain dedicated implementations and examples for each principle.

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✅ Currently Implemented

1️⃣ Single Responsibility Principle (SRP)

A class should have only one reason to change.

This example demonstrates SRP using a simple shopping cart system.

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🏗 Project Structure

designPrinciples/
│
├── src/
│   ├── Main.java
│   └── solidPrinciples/
│       └── srp/
│           ├── Product.java
│           ├── ShoppingCart.java
│           ├── CartRepository.java
│           └── CartInvoicePrinter.java

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🎯 Responsibility Breakdown

Product

• Stores product name and price.
• No business logic.

ShoppingCart

• Adds products.
• Calculates total price.
• Handles cart-related business logic only.

CartRepository

• Responsible for saving cart data.
• Handles persistence only.

CartInvoicePrinter

• Responsible for printing invoice.
• Handles presentation only.

Main

• Client code to demonstrate usage.

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🚀 Why This Follows SRP

Instead of putting:

• Cart logic
• Database logic
• Printing logic

Inside a single class ❌

We separate them into individual responsibilities ✅

This makes the code:

• Easier to maintain
• Easier to extend
• Easier to test
• Cleaner and scalable

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▶️ How to Run

1. Open in IntelliJ IDEA (or any Java IDE).
2. Configure JDK.
3. Run Main.java.

Expected Output

[DB] Saving 1 items to database.
--- INVOICE ---
GT 650 Chrome : ₹400000.0
TOTAL: ₹400000.0
Structure Verified, SRP

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🚧 Upcoming Implementations

This repository will progressively include:

• Open/Closed Principle (OCP)
• Liskov Substitution Principle (LSP)
• Interface Segregation Principle (ISP)
• Dependency Inversion Principle (DIP)

Each principle will have:

• A bad design example ❌
• A refactored SOLID-compliant version ✅
• Clear explanation

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🧠 Purpose of This Repository

• Strengthen understanding of SOLID principles
• Prepare for Low-Level Design interviews
• Practice writing clean and maintainable code
• Build strong object-oriented fundamentals

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This is an evolving repository where all SOLID principles will be implemented step-by-step 🚀

Made with Love ❤️ by Saksham

Aspiring Low-Latency Systems Engineer

GitHub | LinkedIn | Blog | Youtube (Just for Updates)

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