Grokking SOLID Design Principles
Master the SOLID design principles to write clean, scalable, and maintainable code in Java, Python, C++, C#, and JavaScript.
Course Overview
Most engineers can recite the five SOLID principles. Far fewer can look at an unfamiliar class, say which principle it breaks, and explain what the fix will cost. That gap is what this course is written for. Every principle starts from code that violates it. The lesson explains exactly what breaks and why, then refactors it, with each example given in Java, Python, C++, C#, and JavaScript. Most of the examples run in the browser, so you can change one and watch the output change with it. The course is deliberately short: 30 lessons across 7 chapters, an intro, one chapter per principle, and a closing chapter that takes a single class through all five in order. That final chapter also covers the design round itself, including how to name a problem out loud and the questions interviewers actually ask. It tells you where each principle stops being worth applying, which is the part most explanations leave out. Applied without judgement these principles produce a maze of interfaces with one implementation each, so every recommendation here comes with its cost.
What you'll learn in Grokking SOLID Design Principles
- The five SOLID principles a chapter at a time: single responsibility, open closed, Liskov substitution, interface segregation, and dependency inversion.
- What actually counts as one responsibility: not one thing, but one group of people who can ask you to change the class.
- The full Liskov contract of preconditions, postconditions and invariants, including a square that returns a wrong area and never throws an error.
- Dependency inversion as it is actually practised: dependency injection, the service locator pattern, inversion of control frameworks such as Spring, and plugin architectures.
- Why the open closed principle is about planning extension points, not about never editing a file again, which is where most explanations of it go wrong.
- How to name a design problem out loud in a design round, plus nine common SOLID interview questions with model answers.
- Each principle shown as broken code first, then the reason it is broken, then the fix, so you meet the smell before you meet the rule.
- Cohesion, coupling and separation of concerns, and why splitting a class improves the first without automatically improving the second.
- Five signals that an interface is too wide, and the harder question of how small is too small, answered with role interfaces.
- A capstone that takes one checkout class through all five principles in order, ending with the same class wired once for production and once for a test.
- When not to apply these principles, which is the part most explanations leave out and the part interviewers listen for.
- Code examples in Java, Python, C++, C#, and JavaScript, so you see each principle in the language you write rather than in pseudocode.
Course Content
S - Single Responsibility Principle (SRP)
Introduction to the Single Responsibility Principle
What Counts as One Responsibility
Cohesion and its Relation to the Single Responsibility Principle (SRP)
Coupling and its Relation to the Single Responsibility Principle (SRP)
Separation of Concerns
SRP vs. Coupling, Cohesion, & Separation of Concerns
Single Responsibility Wrap Up
D - Dependency Inversion Principle
Putting It Into Practice
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About the Author
Arslan Ahmad
Industry Expertise & Leadership
Arslan Ahmad is the lead author of Grokking SOLID Design Principles. As the founder of Design Gurus and a former FAANG hiring manager, he has worked at industry giants like Facebook (now Meta) and Microsoft.
He has conducted hundreds of system design interviews, giving him unique insight into what top tech companies look for in candidates.
The course also incorporates expertise from senior engineers at Google, Meta, Amazon, Microsoft, and Uber, ensuring you learn system design best practices from professionals who have built and scaled real-world systems.
500+
Interviews Conducted
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Students Taught
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FAQs
What is Grokking SOLID Design Principles?
It is a short, focused course on the five SOLID principles, with one chapter per principle and a closing chapter that applies all five to a single class. Each chapter starts from code that violates the principle, explains precisely what breaks and why, then refactors it, with the examples given in Java, Python, C++, C#, and JavaScript.
Who is this course for?
Engineers preparing for a low level design, object oriented design, or machine coding round, and working developers who want their code reviews to stop turning into arguments. It is also useful before a senior or staff interview, where you are expected to justify a design rather than just produce one.
Do I need to know design patterns before taking this?
No, and the order is usually the other way around. SOLID is the set of principles that explains why most design patterns exist, so learning these first makes the patterns look like consequences rather than a list to memorise.
Which programming languages are the examples in?
Java, Python, C++, C#, and JavaScript. The principles themselves are language independent, but seeing the same violation and the same fix expressed in your own language removes a lot of translation friction, especially for interface segregation and dependency inversion where the language features differ.
How long is the course?
It is deliberately short: 30 lessons across 7 chapters, an intro, one chapter per principle, and a closing chapter that puts them together. It is designed to be finished in a sitting or two, which makes it a realistic thing to do the week before an interview rather than a course you start and abandon.
Does the course say when not to apply these principles?
Yes, and that is deliberate. Applied without judgement these principles produce a maze of interfaces with one implementation each, so the course states the cost of each move as well as the benefit, and the closing chapter has a section on where each principle stops being worth it. Knowing the limits is also what interviewers listen for.
Does it cover the interview round itself?
The final chapter does. One lesson covers how to name a design problem out loud, since the round grades whether you can justify a design rather than whether you can recite five acronyms, and another works through nine common questions including the difference between SRP and ISP and between dependency inversion and dependency injection.
Will this help in a system design interview?
Indirectly. SOLID is about the design of classes inside one application, so it maps onto the low level design or object oriented design round rather than the distributed systems one. That said, the reasoning it trains, spotting a responsibility that belongs somewhere else, is the same instinct that draws good service boundaries.
Is this only useful for interviews?
No. The material is written around code you would plausibly own: a class that has grown too many responsibilities, an interface nobody can implement cleanly, a subclass that surprises its callers. The interview value is real, but the day to day value of being able to name what is wrong with a design is larger.
Do I need prior experience to take this course?
You should be comfortable writing object oriented code, with classes, interfaces, and inheritance. Beyond that, nothing. Each principle is introduced from first principles with a worked example before any of the harder material builds on it.
Is the course text-based or video-based?
Text-based, with diagrams and side by side code examples. Since almost every lesson is a comparison between a broken version and a fixed version, having both on the page where you can look back and forth beats watching them scroll past. All 51 code examples run in the browser, so you can change one and see what happens.
Do I get a certificate of completion?
Yes. Design Gurus issues a certificate once you have completed the course, and you can share the link directly or add it to your LinkedIn profile.
