Interview Q&A

Short answer: Statelessness → Each request is independent; the server doesn’t store client state.

Explain a bit more

Client-Server Architecture → Separation of concerns between client UI and server logic. Uniform Interface → Standard HTTP methods and URIs. Cacheable → Responses can be cached to improve performance. Layered System → APIs can use intermediaries (like load balancers, proxies). Resource-based → Everything is treated as a resource (like users, orders, products).

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: uthorization: Bearer <token>

Real-world example (ShopNest)

ShopNest mobile app sends a JWT Bearer token. The API validates it and uses the user id from claims to load that user’s cart only.

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: Client sends token in Authorization header: Authorization: Bearer <token>

Real-world example (ShopNest)

ShopNest exposes REST APIs for cart and checkout. Controllers stay thin; business rules live in application services.

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: REST → Lightweight, uses HTTP, usually JSON, easy to use, stateless. SOAP → Protocol-based, uses XML, more complex, built-in security & transactions. REST is more flexible and widely used for web and mobile apps.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: Stateless means the server does not store client session data. Each request must contain all the necessary information (like authentication tokens). This makes APIs scalable and reliable.

Real-world example (ShopNest)

ShopNest exposes REST APIs for cart and checkout. Controllers stay thin; business rules live in application services.

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: Platform-independent (works across web, mobile, IoT). Simple, flexible, and scalable. Uses existing HTTP infrastructure. Lightweight (JSON/XML). Supports caching for better performance.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: Easier to learn & implement. Supports multiple formats (JSON, XML, plain text). Faster (less overhead). Works seamlessly with modern web & mobile apps. Better performance due to caching & statelessness.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: Suppose we have a User Service API: GET /users → Get all users GET /users/1 → Get user with ID=1 POST /users → Create a new user PUT /users/1 → Update user with ID=1 DELETE /users/1 → Delete user with ID=1 This shows how CRUD operations map directly to HTTP methods.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: HATEOAS (Hypermedia As The Engine Of Application State) means responses contain links to related actions/resources. 👉

Example code

{ "id": 1, "name": "John", "links": [ { "rel": "self", "href": "/users/1" }, { "rel": "orders", "href": "/users/1/orders" } } This helps clients navigate APIs dynamically.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: Common methods: API Keys → Simple tokens. Basic Auth → Username & password (not secure without HTTPS). OAuth 2.0 / OpenID Connect → Standard protocols for secure access. JWT (JSON Web Tokens) → Widely used for stateless authentication.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: GET → Used to retrieve data, should not modify server state, and can be cached/bookmarked. POST → Used to create new resources or submit data. It modifies server state, is not idempotent, and cannot be cached.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: 200 OK → If the resource was successfully deleted and a response body is returned. 204 No Content → If the resource was deleted but no body is needed. 404 Not Found → If the resource does not exist.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: Safe → Because it only retrieves data without modifying server state. Idempotent → Multiple GET requests have the same result; no side effects occur.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: Yes. If the resource does not exist, PUT can create it at the specified URI. Example: 👉 PUT /users/100 → If user 100 doesn’t exist, it will be created.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: PATCH → Updates only the specified fields (partial update). PUT → Replaces the entire resource representation. 👉

Example code

PATCH /users/1 { "email": "new@email.com" } → Updates only the email. PUT /users/1 { "name": "John" } → May overwrite other fields like email if not included.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: PI? The GET method is used to fetch data because it is safe, idempotent, and optimized for retrieval operations.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: The GET method is used to fetch data because it is safe, idempotent, and optimized for retrieval operations.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: PIs? HTTP status codes are 3-digit numbers returned by the server to indicate the result of a client request. They are important because they: Communicate success, failure, or redirection. Help clients handle responses consistently. Provide debugging and monitoring information.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: HTTP status codes are 3-digit numbers returned by the server to indicate the result of a client request. They are important because they: Communicate success, failure, or redirection. Help clients handle responses consistently. Provide debugging and monitoring information.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: It indicates that a new resource was successfully created. Usually returned after a POST request, along with a Location header pointing to the new resource.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: Returned when the request is malformed or invalid, such as: Missing required parameters. Invalid JSON format. Wrong data type provided.

Real-world example (ShopNest)

ShopNest exposes REST APIs for cart and checkout. Controllers stay thin; business rules live in application services.

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: It means the client is not authenticated (missing/invalid credentials). The request cannot proceed without proper authentication (e.g., missing token).

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: It means the client is authenticated but not authorized to access the resource. 👉 Example: A normal user trying to access an admin-only endpoint.

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: It means the resource has not changed since the last request. Commonly used with caching to improve performance (client uses cached version).

Real-world example (ShopNest)

Creating an order is POST /api/orders → 201 with Location header. Fetching is GET /api/orders/{id} → 200 or 404.

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: 503 indicates the server is temporarily unavailable (e.g., maintenance, overload). Best practices: Return a Retry-After header. Use monitoring/alerts to restore service quickly.

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.