What I Learned from 20 Java Interviews: High‑Frequency Questions and Real Experiences

Overview

After changing jobs, I recorded the interview processes and questions from each company I applied to, both for personal reference and to help others.

I am a Java developer with ten years of experience, applying for senior Java engineer positions.

Resumes were submitted only through Boss直聘.

Due to layoffs in a fresh‑food e‑commerce company, I was also a victim and the employer was *菜.

Resume submission started on 2021‑09‑08 and ended on 2021‑09‑18, excluding weekends.

Boss Data

Communications: 500+

Interviews: 20

Resumes submitted: 130+

Because of re‑interviews, I sometimes had up to six interviews in a single day.

Interview Positions

With ten years of Java experience, I applied for senior Java engineer roles, mainly at companies around Wangjing because I live in Shunyi.

Interview Outcomes

Company names are anonymized; screenshots are partially shown.

9‑8: First and second rounds passed, HR round failed – blocked by education level.

9‑9: First round failed – no interaction from the interviewer.

9‑9: First round failed – possibly due to MySQL cluster setup question.

9‑10: On‑site first round failed – basic question, interviewer seemed cold.

9‑13: On‑site failed – HR and business director interview, lack of payment experience.

9‑14: First round only – Java to Go conversion interview, no result.

9‑15: Reached fifth round – drone industry, remote first round, multiple on‑site rounds, CEO interview, awaiting decision.

9‑16: Second round failed – deep technical questions, high salary offer.

9‑16: Directly passed first round – finance‑related role, HR offered salary after one hour.

9‑16: Passed – fresh‑food similar to Hema, both rounds passed, salary identical.

9‑17: Passed – group interview, second round with five interviewers, later declined offer.

9‑17: Passed – education platform backed by NetEase, algorithm double‑pointer question, second round with director, later HR negotiation.

9‑18: First round failed – algorithm question.

In total, 20 companies were interviewed, resulting in three offers, two declined, and one pending negotiation.

High‑Frequency Interview Topics

1. Java Basics

JVM : architecture, garbage collection strategies (G1, CMS), volatile, unsafe.

Collections : HashMap, ArrayList, LinkedList, ConcurrentHashMap – internal structure, resizing algorithm, red‑black tree vs B+ tree.

Locks : AQS, fair vs unfair locks, synchronized vs Lock, lock evolution.

CAS and ThreadLocal : usage scenarios, memory model.

ThreadPool : seven parameters, rejection policies, scaling for CPU‑bound vs IO‑bound tasks.

2. Spring

IOC/AOP/Transaction fundamentals, source code insights, bean scopes.

Spring bean initialization process – lifecycle states and design patterns.

Spring circular dependency resolution – three maps and bean states.

Spring Boot auto‑configuration – key methods and annotations.

3. MySQL

Indexes: clustered vs non‑clustered, B+ tree structure, covering indexes, EXPLAIN plan.

Transaction: ACID, undo log, isolation levels, lock types, MVCC.

Cluster: master‑slave replication, sharding, partitioning.

4. Redis

Data types and typical use cases.

Cache problems and solutions: snowball, breakdown, penetration; multi‑level cache, Bloom filter.

Eviction policies and LRU algorithm sketch.

Persistence: RDB vs AOF.

Cluster modes: master‑slave, sentinel, sharding.

Distributed lock – Redisson, RedLock, watchdog mechanism.

5. MQ

Types: direct, topic, fanout – scenarios.

Distributed usage: high availability, message reliability.

Delay queues: dead‑letter implementation, Redis+SpringBoot, time‑wheel.

6. Microservice Architecture

Core components comparison (e.g., Sentinel, Dubbo, Spring Cloud).

Distributed transaction approaches: 2PC, 3PC, Seata implementation details.

7. Other Topics

Algorithm and design‑pattern basics, project experience presentation, future development plans.

Summary

As a Java engineer, the knowledge base is vast; this article captures the high‑frequency questions encountered during recent interviews across Java fundamentals, Spring, MySQL, Redis, MQ, and micro‑services, providing a concise reference for preparation.