🚀 Java & Spring Boot Interview Masterclass — 2025 Edition

You've been studying Java for months. But when the interviewer asks "How does HashMap work internally?" or "Why doesn't @Transactional work on private methods?" — does your answer cut it?

This PDF was built to make sure it does.

WHAT'S INSIDE

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✅ 27 in-depth questions with 130+ total answers

✅ 10 chapters covering everything interviewers actually test

✅ Production-grade code examples with real-world context

✅ Pro Tips that separate average answers from senior-level ones

✅ Annotations cheat sheet — all critical annotations at a glance

✅ HTTP status codes reference — know them cold

TOPICS COVERED

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📦 Java Core & OOP

JVM internals, JDK vs JRE vs JVM, JIT compilation, all 4 OOP pillars, abstract classes vs interfaces, overloading vs overriding, == vs .equals(), String Pool, StringBuilder vs StringBuffer

📦 Collections Framework

HashMap internals (hashing, treeification, resizing), HashMap vs ConcurrentHashMap vs Hashtable, ArrayList vs LinkedList, Comparable vs Comparator, pagination with Pageable

📦 Multithreading & Concurrency

Thread lifecycle, Runnable vs Callable, start() vs run(), deadlock prevention, ReentrantLock, ExecutorService, thread pools, CompletableFuture, Virtual Threads (Java 21), ThreadLocal

📦 Java 8+ Modern Features

Stream API (intermediate vs terminal), map() vs flatMap(), Optional, lambda expressions, functional interfaces, parallel streams

📦 Exception Handling & JVM Internals

Exception hierarchy, checked vs unchecked, try-with-resources, heap vs stack memory, Metaspace, G1GC vs ZGC, OutOfMemoryError causes

📦 Spring Core — IoC, DI & AOP

Constructor vs field injection, BeanFactory vs ApplicationContext, @Autowired resolution, @Qualifier vs @Primary, AOP pointcuts, @Before/@After/@Around, @Transactional pitfalls

📦 Spring Boot Deep Dive

Auto-configuration mechanics, @ConditionalOn* annotations, Spring Profiles, profile-specific properties, lazy initialization

📦 REST API & Spring MVC

REST annotations, PUT vs PATCH, global exception handling with @RestControllerAdvice, ProblemDetail (RFC 7807, Spring 6), Bean Validation

📦 Spring Data JPA & Database

JpaRepository, query derivation, @Modifying, @Transactional propagation levels (REQUIRED vs REQUIRES_NEW), isolation levels

📦 Security, Microservices & Testing

Spring Security filter chain, JWT authentication, CSRF, OAuth2, Circuit Breaker with Resilience4j, Saga pattern, @WebMvcTest, @DataJpaTest, Testcontainers

WHO IS THIS FOR?

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Freshers preparing for campus placements or first jobs
1–5 year experience engineers targeting mid/senior roles
Backend developers switching to Java/Spring Boot stack
Anyone who wants to walk into an interview feeling fully prepared

WHY THIS PDF HITS DIFFERENT

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❌ Not a list of definitions you could Google

❌ Not a 500-page textbook that takes weeks to finish

✅ Real interview questions asked at top product companies

✅ Answers written the way you should speak in interviews

✅ Code examples you can actually reason through out loud

✅ Pro Tips that tell you what interviewers are actually testing

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91 pages. No filler. Instant download.

Your next Java interview is closer than you think. Be ready for it. 🎯

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Java Springboot Interview Masterclass-2026 Edition