Java interview questions and answers

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.

Component scanning finds @Service classes and registers bean definitions.

Singleton is one instance per container, which is what almost every stateless service should be.

They are all stereotypes on top of @Component.

Constructor injection makes dependencies required and final, which is easier to reason about and to unit test without Spring.

Aspect-Oriented Programming intercepts join points so you can run extra logic without cluttering business methods.

Spring puts a proxy around the bean

Auto-configuration classes are @Configuration beans gated by @ConditionalOnClass and similar, loaded via spring.factories or AutoConfiguration.imports.

If two beans implement the same type, injection is ambiguous and startup fails.

Entities are tied to the persistence context, lazy proxies, and often more fields than the API should expose.

The many side usually owns the foreign key with @ManyToOne, which is the side you need for inserts.