SOLID Principles Explained Simply

The SOLID principles are five guidelines that help developers write software that’s easy to maintain, flexible, and easy to change.

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1. S — Single-Responsibility Principle (SRP)

Each module or class should have one reason to change.
In simple terms: do one job, and do it well.

Bad:

class Report {
  generate() {/* ... */}
  saveToDatabase() {/* ... */} // ❌ different responsibility
}

Good:

class ReportGenerator { generate() {/* ... */} }
class ReportSaver { saveToDatabase() {/* ... */} }

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2. O — Open-Closed Principle (OCP)

Software entities should be open for extension but closed for modification.
You should be able to add new behavior without touching existing, stable code.

Example:
Instead of editing a payment processor class every time you add a new method, create a new class implementing the same interface.

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3. L — Liskov Substitution Principle (LSP)

Subclasses should behave like their parent classes.
Replacing a parent object with a child should not break your program.

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4. I — Interface Segregation Principle (ISP)

Clients should not depend on methods they don’t use.
Create many small, specific interfaces instead of a single “god” interface.

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5. D — Dependency Inversion Principle (DIP)

High-level modules should depend on abstractions, not on low-level details.
Abstractions shouldn’t depend on details—details should depend on abstractions.

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✨ Why SOLID Matters

• ✅ Easier to maintain – changes in one place have fewer ripple effects.
• 🧪 More testable – smaller, focused units are easier to test.
• 🔁 Reusable & scalable – modular code can grow without chaos.

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📌 Quick Reference

Principle	Meaning (Simplified)
SRP	One job per module/class
OCP	Extend without modifying
LSP	Subclasses act like parents
ISP	Use only what you need
DIP	Depend on abstractions

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That’s SOLID—five simple habits that make your code cleaner, safer, and easier to grow.