Design principles questions reveal whether you write code that other engineers want to work with. Interviewers aren’t looking for you to recite SOLID — they want to see that you can apply these principles pragmatically, knowing when to follow them and when to bend them.
These 6 questions cover the design principles that matter most in production codebases: SOLID principles with real trade-offs, composition vs inheritance decisions, and when DRY and KISS actually conflict. The kind of judgment that separates engineers who write clean code from those who over-engineer it.
The Singleton pattern restricts a class to a single instance and provides a global access point to it.
Read full answer →The Factory pattern is a creational design pattern that encapsulates object creation logic behind an interface, so callers don't need to know which concrete class they're instantiating.
Read full answer →The Strategy pattern is a behavioral design pattern that defines a family of algorithms, encapsulates each one, and makes them interchangeable.
Read full answer →The Observer pattern (also called Publish-Subscribe or Event Listener) defines a one-to-many dependency between objects: when the **subject** (publisher/observable) changes state, all registered **observers** (subscribers/listeners) are notified and updated automatically.
Read full answer →Inversion of Control (IoC) is a design principle where the control of object creation and dependency management is transferred from the object itself to an external entity (a framework or container).
Read full answer →**Cohesion** measures how strongly related the responsibilities inside a single module or class are.
Read full answer →Focus on understanding concepts deeply enough to explain them in your own words. For each topic, practice articulating the trade-offs and real-world applications — interviewers care about practical judgment, not textbook definitions.
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