Java backend loops still lean heavily on Spring Boot, REST design, persistence, and JVM fundamentals. Interviewers mix textbook definitions with “how did you use this in production?”
Core Java topics
- OOP — encapsulation, inheritance, polymorphism, composition vs inheritance.
- Collections and streams — when to use which structure, common pitfalls.
- Concurrency — thread pools, CompletableFuture, synchronized vs locks, virtual threads (where relevant).
- JVM basics — garbage collection at a high level, memory leaks you have seen.
Spring Boot topics
- Dependency injection and bean scopes.
- REST controllers, validation, exception handling, and API versioning.
- Spring Data JPA — transactions, N+1 queries, lazy loading issues.
- Security — authentication vs authorization, JWT or session patterns you shipped.
- Testing — unit vs integration, Testcontainers for databases.
Turn definitions into experience answers
After explaining polymorphism or dependency injection, bridge to a project: “In our billing service we used…” Load resume bullets that mention Java and Spring before the interview so your copilot can suggest company-specific details when you get a rapid-fire sequence of questions.