Interview Q&A

Short answer: Use API contracts and versioning. Employ service discovery and load balancing. Prefer asynchronous messaging/event-driven architecture to reduce tight coupling. Apply circuit breakers and retries for fault tolerance.

Real-world example (ShopNest)

Patterns in ShopNest should solve a real pain (swappable payments, test seams)—not be added for decoration.

Say this in the interview

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

Short answer: Interfaces define contracts with no implementation, supporting ISP and DIP by allowing flexible implementations. Abstract classes provide a base implementation and shared code, useful for Template Method pattern and partial abstraction.

Example code

Interfaces define contracts with no implementation, supporting ISP and DIP by allowing flexible implementations. Abstract classes provide a base implementation and shared code, useful for Template Method pattern and partial abstraction.

Real-world example (ShopNest)

Open/Closed in ShopNest: add a new payment method by adding a class, not by editing a giant switch in CheckoutService.

Say this in the interview

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

Short answer: Builder separates complex object construction from its representation. For example, building an HttpRequest with optional headers, query params, and body: public class HttpRequestBuilder

Example code

{
private HttpRequestMessage _request = new HttpRequestMessage();
public HttpRequestBuilder SetMethod(HttpMethod method)
{
_request.Method = method;
return this;
}
public HttpRequestBuilder AddHeader(string key, string value)
{ _request.Headers.Add(key, value); return this;
}
public HttpRequestMessage Build() => _request;
} Allows building requests step-by-step fluently.

Say this in the interview

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

Short answer: Observer supports SRP by separating notification logic from core business logic and DIP by depending on abstractions (observers). It fits DI because observers can be injected, allowing flexible runtime subscriptions and loose coupling.

Real-world example (ShopNest)

ShopNest payment fees use Strategy: IFeeCalculator with UPI/Card implementations chosen at runtime.

Say this in the interview

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