SOLID Principles Made Simple (With Examples)

The SOLID principles are five design principles in Object-Oriented Programming (OOP) that help developers write clean, scalable, and maintainable code.

Each principle ensures that software is easy to modify, extend, test, and understand. Let’s break them down with real-life examples and code snippets in Java.

1. Single Responsibility Principle (SRP)

🔹 What is it?

A class should have only one reason to change, meaning it should have only one job.

📌 Real-Life Example:

Imagine a Restaurant. The Chef cooks food, and the Cashier handles payments.

• If the Chef also handles billing, the system becomes hard to manage.
• So, each role (class) should have only one responsibility.

📌 Bad Code (Violating SRP)

class Restaurant {
    void cookFood() {
        System.out.println("Cooking food...");
    }

    void processPayment() {
        System.out.println("Processing payment...");
    }
}

🔴 Problem:

• The Restaurant class does two things: cooking and handling payments.
• If we need to change how payments work, we modify the same class, increasing the risk of breaking something.

📌 Good Code (Following SRP)

class Chef {
    void cookFood() {
        System.out.println("Cooking food...");
    }
}

class Cashier {
    void processPayment() {
        System.out.println("Processing payment...");
    }
}

✅ Now:

• The Chef class handles cooking.