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Start by clarifying requirements and scope, then identify core entities and their relationships. Use abstract classes for shared state/behavior and interfaces for capabilities, explaining trade-offs. Walk through a concrete example like a parking lot to demonstrate the hierarchy.
Pro tip: Emphasize that interfaces define contracts for 'can-do' capabilities (e.g., Payable) while abstract classes provide 'is-a' foundations with partial implementation, and justify choices based on extensibility and avoiding the fragile base class problem.
Ask clarifying questions to understand functional and non-functional requirements, such as scale, concurrency, and extensibility needs. This ensures the design addresses the right problems.
List the main objects (e.g., ParkingLot, ParkingSpot, Vehicle) and their interactions. Determine which are nouns and how they relate (inheritance, composition, aggregation).
For each entity, decide if it should be an abstract class (shared state/behavior) or an interface (capability contract). Explain your reasoning based on code reuse and flexibility.
Sketch the hierarchy, showing abstract classes, concrete classes, and interfaces. Use a simple diagram or verbal description to illustrate relationships.
Explain why you chose certain abstractions and how they support future changes, such as adding new vehicle types or payment methods, without modifying existing code.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Easier once the class diagram was on the board.
Pick a concrete project you know well and narrate the design decisions around inheritance, composition, and polymorphism as a story of trade-offs. Explain why you chose each structure, what alternatives you considered, and how the choice impacted maintainability, extensibility, and testability. Keep the focus on your reasoning, not just the mechanics.
Pro tip: Emphasize that you favor composition over inheritance by default, but show you know when inheritance is justified—like when there's a true is-a relationship with shared behavior and a stable hierarchy. Mention that you've refactored away from deep inheritance trees when they became brittle.
Briefly describe the project or feature you'll use as an example, including its scale and your role. This grounds the discussion and shows you can communicate technical context clearly.
Describe where you used inheritance, why it was appropriate (e.g., shared interface with default behavior), and any pitfalls you avoided. If you avoided inheritance, explain why composition was better.
Detail how you used composition to assemble behavior, promote flexibility, and reduce coupling. Give a specific example of a class that delegates to collaborators.
Show how polymorphism enabled extensibility—e.g., swapping implementations at runtime, using interfaces for dependency injection, or supporting multiple algorithms. Connect it to testability and open/closed principle.
Summarize why these structural choices were right for the context, what you might change, and how they affected the team's velocity or code quality. This demonstrates maturity and self-awareness.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by briefly recapping the key components of your design, then map each SOLID principle to specific classes, interfaces, or modules you created. Use concrete examples from your design to show how each principle improved maintainability, extensibility, or testability, and be honest about any trade-offs.
Pro tip: Don't just list the principles—explain how applying them made your design better for Microsoft's scale and evolving requirements, and acknowledge any areas where you consciously deviated from SOLID for pragmatic reasons.
Briefly summarize the system's architecture and key components so the interviewer has context for your SOLID examples.
For each SOLID principle, point to a concrete class, interface, or module in your design and explain how it embodies that principle.
Describe how applying each principle improved the design's flexibility, testability, or maintainability, and how it would help with future changes.
Acknowledge any areas where you intentionally relaxed a SOLID principle for performance, simplicity, or other constraints, and justify your decision.
Tie your SOLID application to Microsoft's engineering practices, such as scalability, reliability, and long-term maintenance of large codebases.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.