Interview prep216 interview questions,
216 interview questions,
answered properly.
Every answer explains the why, shows code where it helps and flags the follow-up questions interviewers love. Filter by difficulty, mark what you already know and focus on the gaps.
Modern Java
Core Java & OOPOOP, the type system, String, equals/hashCode, exceptions and the language fundamentals every Java interview starts with.20 questionsCollectionsHashMap internals, List/Set/Map trade-offs, fail-fast iterators, concurrent and immutable collections.14 questionsJava 8+ — Lambdas, Streams & OptionalFunctional interfaces, method references, the Stream API, collectors and Optional — including the classic live-coding questions.16 questionsModern Java (17–21)Records, sealed types, pattern matching, switch expressions, text blocks, var and virtual threads.14 questionsConcurrency & MultithreadingThreads, executors, synchronized vs volatile, the memory model, locks, atomics, deadlocks and CompletableFuture.18 questionsJVM, Memory & PerformanceHeap vs stack, garbage collection, collectors, memory leaks, class loading, the JIT and diagnosing production issues.13 questions
Spring Boot 4
Spring CoreIoC and DI, bean scopes and lifecycle, configuration, AOP and proxies — the Spring Framework 7 fundamentals behind every Boot application.17 questionsSpring Boot 4 & REST APIsAuto-configuration, starters, configuration and profiles, REST design, validation, error handling, HTTP clients and what's new in Boot 4.17 questionsSpring Data JPA & TransactionsRepositories, entity mapping, fetching and N+1, transactions, propagation, isolation and locking.17 questionsSpring Security & TestingThe security filter chain, authentication, JWT and OAuth2, method security, CSRF/CORS — and testing strategy with slices, @MockitoBean and Testcontainers.17 questionsMicroservices & ProductionService boundaries, communication styles, resilience, Kafka, caching, observability, deployment and the distributed-systems questions senior roles expect.20 questions
Design Patterns
Design PatternsCreational, structural and behavioural Gang of Four patterns — intent, trade-offs, comparisons and where Java and Spring use them.22 questionsSOLID & Object-Oriented DesignThe SOLID principles, composition vs inheritance, coupling and cohesion, and low-level design questions.11 questions