If you’ve ever felt like the SOLID principles sound too abstract, don’t worry; in this article we’ll break them down into simple, relatable examples with analogies. By the end, you’ll understand each one in a way you’ll never forget. Let’s dive in!
1. Single Responsibility Principle (SRP)
This means one class should only do one job. Think of your phone. You have a camera app to take pictures, you have a messaging app to send messages, and you have a music app to play songs.
Each app does one job well. If your camera app also tried to send messages and play music, it would become messy and hard to maintain.
In code terms, this means:
❌ Don’t do this:
✅ Do this:
Each class does one thing well, making it easier to maintain, test, and reuse.
2. Open/Closed Principle (OCP)
This means classes should be open for extension but closed for modification. In the sense that you should be able to add new features without changing existing code.
Example:
Imagine you have a payment system. Initially, it only supports credit cards.
Now, if you want to add PayPal, you’d need to edit the same class, which risks breaking existing code.
✅ Better approach:
Now you can extend by adding new classes instead of editing old ones.
3. Liskov Substitution Principle (LSP)
This is only saying that a subclass (child class) should be able to replace its parent class without breaking things.
Example with birds:
This breaks LSP. Even though Penguin is a bird, substituting it as a flying bird is wrong.
✅ Fix: Split responsibilities
Solution:
Bird = general parent class
FlyingBird = parent class for birds that fly
Eagle = subclass (child class) that can fly
Penguin = subclass (child class) that doesn’t fly
Now we can substitute any subclass correctly without confusion.
4. Interface Segregation Principle (ISP)
Here, although the principle name is like a combination of big words, here is what it simply means. Don’t force a class to implement things it doesn’t need.
Example:
Let’s say we have a Worker interface:
Now, we create a Robot class:
The robot is forced to implement Eat() even though it doesn’t need it.
✅ Fix: split into smaller interfaces:
Now a robot who is also a worker doesn’t need to implement Eat().
5. Dependency Inversion Principle (DIP)
This principle is saying we should rely on abstractions, not on concrete implementations, as it makes it easier to add features without breaking or modifying our existing code and ensures testing works flawlessly.
Example:
Imagine your phone and apps again. Your phone doesn’t care if you install WhatsApp, Telegram, or Signal. It just says, “I’ll allow any messaging app as long as it follows the rules.”
In code:
❌ Without DIP:
Here Notification is stuck with Email.
✅ With DIP:
Now you can swap email, SMS, or even WhatsApp without changing notifications.
Bonus: Why SOLID Matters So Much
It’s important to know that SOLID isn’t just about writing “good code.” This is like saying, "Your smartphone, even though it has multiple features like browsing, playing music, watching movies, etc., you just want to restrict to making/receiving calls." SOLID is more than that. It’s about writing maintainable, scalable, and flexible code that doesn’t break when you add new features. You might not know the magnitude of this when you're writing your code from the initial start, but a few years down the line when you have to maintain or add features to code another developer wrote, or even if you wrote it, if SOLID was applied at the inception of the code, you'll appreciate it massively because it'll make your work a lot easier.
By following SOLID, your code becomes easier to test, you reduce bugs, and you can adapt faster to changes
SOLID might look intimidating at first, but when you think about apps on your phone, birds that may or may not fly, and robots that don’t eat, it becomes much easier to digest.
Once you practice applying it, you’ll never forget it.
This is the layman’s guide to SOLID I promised. What do you think? Did I break it down enough for your easy assimilation? Drop your opinions in the comment section.
I remain Omotola Odumosu. Catch me on my socials below.
Top comments (2)
Awesome explainer! Could you share any recommended resources—books, articles, or sample repos—for diving deeper into SOLID, especially real-world examples and common pitfalls?
Thanks so much for reading and for the “awesome explainer” shout-out! 🙌 …Comments like yours really encourage me to keep writing posts like this.
I don’t have a full curated list yet, but this is a great nudge for me to start one in the future. Meanwhile, here are a few resources I suggest :
Head First Design Patterns (O’Reilly) → Beginner-friendly, uses analogies & visuals (very much like my post).
Clean Architecture (Uncle Bob) → More advanced, shows SOLID in the bigger system context.
Since SOLID can be applied in any programming language, I’m not sure which one you’re using. But if it’s C#, this repo is nice:
github.com/gopikrishnareddy93/SOLI...
PS: If anyone else has favorite resources, feel free to drop them here. it’ll help all of us! 🚀