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Timed mock tests and model answers written by working engineers, for every level from fresher to lead. Pick any of our 75 courses below.

Topic: Java & Spring Boot. Questions are shared by related courses. View the Java course →

All Java interview questions at a glance+

Fresher (0–3 years): Junior Java Developer

  1. Explain the four pillars of OOP with Java examples.
  2. ArrayList vs LinkedList: when would you use each?
  3. How do you build a REST API with Spring Boot?
  4. What does the JVM do?
  5. == vs equals() for strings?
  6. Which collection keeps unique elements?
  7. What is method overloading?
  8. Spring Boot is mainly used to…
  9. Checked exceptions must be…

Mid-level (3–8 years): Java Developer

  1. A Spring Boot service has rising response times. How do you investigate?
  2. How do you secure a Spring Boot REST API?
  3. Explain Java memory: heap, stack and garbage collection.
  4. What does stream().filter(x -> x > 2).map(x -> x * 2).toList() do on [1, 2, 3, 4]?
  5. Which keyword ensures visibility of a variable across threads?
  6. What does @Transactional ensure?
  7. An N+1 query problem in JPA is fixed by…
  8. ConcurrentHashMap is preferred over a synchronized HashMap because…
  9. Which tool helps diagnose high memory usage in a JVM?

Experienced (8–15 years): Senior Java Engineer / Architect

  1. Design a scalable order-processing system in Java.
  2. How would you migrate a large Spring app to newer Java and Spring versions?
  3. How do you lead code quality in a Java team?
  4. Virtual threads (Java 21) mainly help…
  5. Resilience patterns between microservices include…
  6. Breaking a monolith is best done with…
  7. Event-driven communication via Kafka mainly provides…
  8. Choosing a GC for low-latency services, you would evaluate…
  9. Records (Java 16+) are useful for…