Comprehensive List of Java Interview Topics and Questions

Basic Questions

Java thread states; differences between processes and threads and their communication; HashMap structure and differences with Hashtable and ConcurrentHashMap; Cookie vs Session; purpose and creation of indexes; ArrayList implementation, differences with LinkedList, and resizing; equals method implementation; object‑oriented concepts; distinction between BLOCKED and WAITING thread states; JVM class loading; JVM garbage collection algorithms and when Full GC or Young GC occurs; JVM memory model; Java runtime data areas; transaction implementation principles.

Technical Depth

Experience with JDK source code; HTTP and TCP protocols; consistent hashing algorithm; class loader unloading; IO vs NIO differences; Java thread pool internals and keepAliveTime; HTTP connection pool implementation; database connection pool and database internals.

Frameworks

Knowledge of open‑source framework source code; Redis advantages, disadvantages and scaling; Netty thread‑pool usage; reasons for using Spring, its pros and cons; Spring IOC container initialization and bean resolution mechanisms; Spring AOP internals; message‑queue middleware implementation challenges.

System Architecture

Designing highly available systems; design patterns that improve extensibility (template, command, strategy, adapter, bridge, decorator, observer, state, visitor); improving development efficiency; high cohesion and low coupling with examples; when to use interfaces versus messages; decoupling inter‑dependent systems; writing design documents; criteria for splitting or merging systems; differences between systems and modules.

Distributed Systems

Two‑phase commit for distributed transactions; distributed lock and session implementation; ensuring message consistency; load balancing; forward and reverse proxy concepts; CDN principles; techniques to increase QPS and throughput.

Practical Ability

Handling production incidents such as memory leaks, high CPU, unresponsive applications; solving technical problems encountered during development; designing a high‑concurrency whitelist lookup with daily updates; how Weibo pushes updates to followers; how Google returns search results within a second; 12306 ticket‑booking system preventing overselling; designing a flash‑sale system that limits purchases.

Soft Skills

Learning new technologies effectively; staying updated with emerging tech; managing heavy and diverse workloads; handling project delays; reconciling differing design ideas with colleagues; ensuring development quality; short‑ and long‑term career planning; team planning; personal growth reflections.

Java Architect Standards

Proficiency with Java frameworks and their underlying principles; deep understanding of JVM internals and tuning; mastery of object pools, connection pools, thread pools; reflection and bytecode alternatives; NIO direct memory usage; multithreading synchronization; collection implementations (e.g., HashMap resizing); data structures and algorithms; Linux system expertise; TCP three‑way handshake and four‑way termination; HTTP header, session and cookie lifecycle; clustering, load balancing, reverse proxy, static site generation; distributed storage (NFS, FastDFS, Hadoop); caching (Redis, Memcached) and consistent hashing; Nginx usage; MySQL design, optimization, replication, and basic NoSQL (MongoDB); message‑queue middleware for asynchronous processing.

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