Java Interview
Complete Guide

Core Java concepts, OOP fundamentals, memory model, and language basics every Java developer must know.

Java 5 through Java 21+ — generics, lambdas, streams, modules, records, sealed classes, virtual threads.

SOLID principles, design patterns, composition vs inheritance, interfaces, abstract classes.

Arrays, Linked Lists, Stacks, Queues, Trees, Graphs, Hash Maps, Heaps, Tries · Searching (Binary, Cyclic Sort) · Sorting (Merge, Quick, Heap, Radix) · Patterns (Two Pointers, Sliding Window, DP, Backtracking, Greedy, Union-Find, Dijkstra) — with visual diagrams and problem maps for every concept.

List, Map, Set internals — ArrayList vs LinkedList, HashMap internals, TreeMap, generics, iterators.

Exception hierarchy, checked vs unchecked, try-with-resources, custom exceptions, best practices.

Threads, locks, executors, concurrent collections, CompletableFuture, virtual threads, Project Loom.

StampedLock, Scoped Values, Disruptor, NUMA, reactive streams, JFR profiling, expert-level patterns.

Theory + tricky output puzzles + hands-on coding — Strings, Arrays, Collections, Maps, Streams, Optional, Comparator and real interview challenges.

Arrays · Strings · OOP · Collections · Generics · Design Patterns · System Design · Math edge cases (10/0, 10.0/0.0, NaN) · Exceptions · Concurrency · Streams · JVM · Modern Java 8→21 · Spring Core · Spring Boot · Spring Data — instant scoring + explanations.

Quick revision tables for 320+ methods — String, Collections, Stream, Math, Optional, Comparator and more, with behavioral notes.

Spring overview and original comprehensive Q&A (282+ questions). Choose a focused deep-dive section below.

IoC, DI, Bean lifecycle, core annotations, auto-configuration, Profiles, REST API and validation — deeply explained with real-world analogies and code.

Security filter chain, JWT from scratch, AOP internals, @Cacheable, @Async, Testcontainers testing — production-depth implementation detail.

JPA Persistence Context, N+1 fixes, @Transactional, Kafka delivery guarantees, Resilience4j circuit breaker, zero-downtime K8s deployment.

Separate deep pages for Databases, Architecture, Cloud/Deployment, CI/CD + Tooling, and Observability + Analytics with beginner-to-expert progression.