101 Must-Know Java Interview Questions & Answers
The battle-tested revision kit covering JVM internals, Concurrency, Collections, Spring Boot 3, and tricky interviewer traps. Read in 90 minutes before your next technical round.
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Why Smart Engineers Keep Getting Rejected in Java Rounds
Most candidates fail not because they don’t know Java, but because they give generic, surface-level definitions when senior interviewers ask about edge cases (e.g. “What happens during HashMap hash collisions at scale?”, “Why does self-invocation break Spring @Transactional?”, or “How does ConcurrentHashMap avoid locking reads?”).
This 101-question blueprint cuts out 500 pages of fluff and gives you the exact architectural answers and code snippets senior interviewers look for.
What’s Inside the 101 Questions Blueprint
- Module 1: JVM Architecture & Memory Model: Stack vs Heap, Metaspace, GC algorithms, JIT compiler optimizations.
- Module 2: Core OOP & String Internals: Immutability security, String Constant Pool mechanics, dynamic method dispatch.
- Module 3: Collections Deep Dive: HashMap treeification, fail-fast vs fail-safe iterators, custom key contracts (`equals` + `hashCode`).
- Module 4: Concurrency & Multithreading: CAS hardware instructions, `volatile` vs `synchronized`, lock-free reads in ConcurrentHashMap, ThreadPool starvation.
- Module 5: Modern Java (Java 8 to 21): Stream pipelines, loop fusion, CompletableFuture, Virtual Threads vs Platform Threads, Records & Pattern Matching.
- Module 6: Spring Boot 3 & Microservices: Bean lifecycles, AOP proxy boundaries, Circuit Breakers, Distributed Tracing with MDC.
- Module 7: JPA & Hibernate Performance: N+1 query elimination, first/second-level cache, dirty checking internals.
- Module 8: Tricky Coding & Output Traps: 15 classic trick questions with step-by-step visual explanations.
“I had my TCS digital and Cognizant technical rounds back-to-back. Skimming this PDF the night before helped me answer the multithreading and JPA cache questions without hesitation. Got selected in both!”
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