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What are interfaces?

Q: What are interfaces?

Short answer: Interfaces define a contract of methods, properties, or events that implementing classes must follow. Interfaces provide full abstraction without any implementation (C# 8+ allows default methods). interface IFlyable Example code { void Fly(); } Real-world example (ShopNest) Checkout calls IPaymentGateway.Charge() . Razorpay and Stripe adapters implement the same interface, so ShopNest can switch gateways without rewriting the order service. Say this in the interview Define — one clear sentence (the short answer above). Example — relate it to a project like ShopNest or your real work. Trade-off — when you would not use it.

Short answer: Interfaces define a contract of methods, properties, or events that implementing classes must follow. Interfaces provide full abstraction without any implementation (C# 8+ allows default methods). interface IFlyable

Example code

{ void Fly(); }

Real-world example (ShopNest)

Checkout calls IPaymentGateway.Charge(). Razorpay and Stripe adapters implement the same interface, so ShopNest can switch gateways without rewriting the order service.

Say this in the interview

Define — one clear sentence (the short answer above).
Example — relate it to a project like ShopNest or your real work.
Trade-off — when you would not use it.

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