Java and backend interview questions

Instead of a class constructing its own collaborators with new, the container passes them in, usually via the constructor.

@Controller is for MVC that returns view names

Both bind to the same Environment

Node.js is a JavaScript runtime built on V8 that uses an event loop for non-blocking I/O.

Middleware is a function (req, res, next) that runs in a pipeline before your route handler.

The event loop registers I/O and runs callbacks when sockets are ready, so one thread can juggle thousands of waiting connections.

Redis is an in-memory data store used as a cache, session store, rate-limit counter, and simple pub/sub.

The database is the system of record and is built for durability and queries.

Unbounded lists blow up memory, latency, and mobile data.

Content-Type describes the body you are sending, for example application/json.

Encapsulation hides fields behind methods so callers cannot break invariants.

== may compare references

401 means unauthenticated — missing or bad credentials.

Success with no body, often after DELETE.

UNION deduplicates

The request clashes with current resource state, like a duplicate unique key or version conflict.

They separate SQL structure from user values so injection is much harder.

Repeating a PUT with the same body should leave the same final state.

Functions that run before the route handler for logging, auth, parsing, and errors.