Unlock 1000+ Java Interview Questions – Free PDF Guide for Developers

The author has compiled a massive Java interview handbook with more than 1,000 questions (approximately 485 pages, 320,000 words) covering a wide range of backend technologies. The guide is available on GitHub and has attracted over 30,000 stars.

MyBatis Interview Questions

What is MyBatis?

Advantages of MyBatis

Disadvantages of MyBatis

Suitable scenarios for MyBatis

Differences between MyBatis and Hibernate

Difference between # and $

How to handle mismatched property and column names?

How to write fuzzy query with LIKE?

How does the DAO interface work with an XML mapper?

How does MyBatis perform pagination? What is the principle of pagination plugins?

What mapping forms does MyBatis use to wrap SQL results into target objects?

How to execute batch inserts?

How to obtain auto‑generated primary keys? How to pass multiple parameters in a mapper?

What is the purpose of dynamic SQL in MyBatis? How does it work? What dynamic SQL types exist?

Besides common select/insert/update/delete tags, what other tags exist in an XML mapper?

Why is MyBatis considered a semi‑automatic ORM tool? How does it differ from fully automatic tools?

How to implement one‑to‑one and one‑to‑many associations? How many ways?

Does MyBatis support lazy loading? If so, how?

What are first‑level and second‑level caches in MyBatis?

What is interface binding in MyBatis and how is it implemented?

Requirements for using MyBatis mapper interfaces?

Different ways to write a mapper?

Explain the plugin mechanism of MyBatis and how to develop plugins.

Zookeeper Interview Questions

What is Zookeeper?

What does Zookeeper provide?

Zookeeper file system

ZAB protocol

Four types of Znode data nodes

Watcher mechanism – data change notification

How does a client register a watcher?

How does the server handle watcher notifications?

Client callback watcher

ACL permission control mechanism

Chroot feature

Session management

Server roles

Server working states

Data synchronization

How does Zookeeper guarantee transaction order consistency?

Why does a distributed cluster need a master? How to handle node failures?

Difference between Zookeeper load balancing and Nginx load balancing

Deployment modes of Zookeeper

Minimum number of machines for a cluster and its rules

Can the cluster dynamically add machines?

Are watcher notifications permanent? Why not?

Java clients of Zookeeper

What is Chubby and how does it compare to Zookeeper?

Common Zookeeper commands

Relation between ZAB and Paxos algorithms

Typical application scenarios of Zookeeper

Dubbo Interview Questions

Why use Dubbo?

What are the layers of Dubbo’s overall architecture?

Default communication framework and alternatives

Is service invocation blocking?

Typical registry centers and alternatives

Default serialization framework and other options

How does Dubbo achieve service degradation and version compatibility?

How to solve long service call chains? Core configuration items?

Recommended Dubbo protocol

Can you directly connect to a specific service when multiple providers exist?

Draw the service registration and discovery flowchart

Dubbo cluster fault‑tolerance schemes

How to implement service downgrade and retry?

Common problems encountered when using Dubbo

Principle of Dubbo Monitor implementation

Design patterns used by Dubbo

How Dubbo configuration files are loaded into Spring

Difference between Dubbo SPI and Java SPI

Does Dubbo support distributed transactions?

Can Dubbo cache results?

How to ensure service upgrades are compatible with old versions

Essential Dubbo dependencies

What can Dubbo telnet command do?

Does Dubbo support service degradation?

How to gracefully shut down Dubbo?

Difference between Dubbo and Dubbox

Difference between Dubbo and Spring Cloud; other distributed frameworks?

Redis Interview Questions

What is Redis?

Data types in Redis

Benefits of using Redis

Advantages of Redis over Memcached

Differences between Memcached and Redis

Is Redis single‑process or single‑threaded?

Maximum size of a string value

Persistence mechanisms of Redis and their pros/cons

Common performance problems and solutions; expiration key deletion strategy

Redis eviction policies

Why does Redis keep all data in memory? Synchronization mechanisms?

Benefits of pipeline and why to use it

Experience with Redis cluster and its principles

When can a Redis cluster become unavailable?

Java clients for Redis and recommended one

Comparison of Jedis and Redisson

How to set and verify passwords in Redis

Concept of hash slots

Master‑slave replication model in Redis cluster

Potential data loss in Redis cluster and reasons

Replication mechanism in Redis cluster

Maximum number of nodes in a Redis cluster

How to choose a database in a cluster

Testing Redis connectivity

Understanding Redis transactions

Redis transaction commands

How to set key expiration and permanent validity

Memory optimization techniques for Redis

How the Redis eviction process works

Ways to reduce Redis memory usage

What happens when Redis memory is exhausted

Maximum number of keys per Redis instance and per data structure

Ensuring hot data stays in Redis when MySQL holds 20 M rows

Best scenarios for using Redis

How to efficiently delete a large number of keys with a common prefix

Considerations when setting the same expiration time for many keys

Using Redis as an asynchronous queue

Using Redis distributed locks

MySQL Interview Questions

Types of locks in MySQL

Different table types in MySQL

Difference between MyISAM and InnoDB

Four transaction isolation levels and their differences

Difference between CHAR and VARCHAR

Difference between primary key and candidate key

Purpose of myisamchk

Effect of defining a column as TIMESTAMP

How to view all indexes of a table

Meaning of % and _ in LIKE statements

Column comparison operators

Difference between BLOB and TEXT

Difference between mysql_fetch_array and mysql_fetch_object

Storage format of MyISAM tables

How to optimize DISTINCT queries

How to display the first 50 rows

Maximum number of columns that can be indexed

Difference between NOW() and CURRENT_DATE()

What are non‑standard string types?

What are common SQL functions?

Does MySQL support transactions?

Best field type for storing monetary values

Permission‑related tables in MySQL

Possible column string types

How to optimize a database that stores >5 M rows daily for three years

Lock optimization strategies

Underlying implementation and optimization of indexes

When an index cannot be used

Practical MySQL optimization methods

Methods to optimize a database

Impact of indexes, primary keys, unique keys, and composite indexes on performance

What is a transaction in a database?

Causes of SQL injection and prevention methods

Choosing appropriate data types for table fields

Storage engines

Importance of indexes in relational databases

Difference between outer join, inner join, and self‑join

Overview of MySQL transaction rollback mechanism

Components of SQL language

Types of integrity constraints

What is a lock?

What are views and cursors?

What is a stored procedure and how to call it?

Explanation of the three normal forms

Difference between base tables and views

Advantages of views

Meaning of HUI.L

Difference between primary key, foreign key, and index

How to enforce column value ranges

SQL statement optimization methods

Java Concurrency Interview Questions

Three essential elements of concurrent programming

Methods to achieve visibility

Value of multithreading

Ways to create threads

Comparison of three thread‑creation methods

Thread state transition diagram

Five basic thread states in Java

What is a thread pool? Creation methods?

Four ways to create thread pools

Advantages of thread pools

Common concurrent utility classes

Difference between CyclicBarrier and CountDownLatch

Purpose of synchronized

Purpose of volatile keyword

What is CAS?

Problems of CAS

What is Future?

What is AQS?

AQS supports two synchronization modes

What is ReentrantLock?

What is FutureTask?

Difference between synchronized and ReentrantLock

Optimistic lock vs pessimistic lock

How does thread B know thread A modified a variable?

Comparison of synchronized, volatile, CAS

Difference between sleep and wait

What is ThreadLocal and its use?

Why must notify/notifyAll be called inside a synchronized block?

Methods of thread synchronization

Thread scheduling strategies

Concurrency level of ConcurrentHashMap

How to find the thread using most CPU in Linux

Java deadlock and how to avoid it

Causes of deadlock

How to wake a blocked thread

How immutable objects help multithreading

What is thread context switching?

What happens when a thread pool queue is full?

Thread scheduling algorithm used by Java

What is a thread scheduler and time slicing?

What is a spin lock?

What is the Lock interface in java.util.concurrent.locks?

Thread‑safety of singleton pattern

Purpose of Semaphore

What is Executors class?

Which thread uses the constructor and static block of a thread class?

Which is better: synchronized method or block?

Exceptions caused by too many Java threads

Spring Interview Questions

What is Spring?

Benefits of using Spring framework

Modules that compose Spring

Core container (application context) module

BeanFactory and its implementations

XMLBeanFactory

Explain AOP module

Explain JBC abstract and DAD modules

Explain ORM integration module

Explain WEB module

Spring configuration files

What is Spring IoC container?

Advantages of IoC

Typical implementation of ApplicationContext

Difference between BeanFactory and ApplicationContext

What does a Spring application look like? Dependency injection

What is Spring’s dependency injection?

Different types of IoC (dependency injection) methods

Which DI method is recommended: constructor or setter?

What are Spring beans?

What does a Spring bean definition contain?

How to provide metadata to Spring container?

How to define bean scope?

Explain bean scopes supported by Spring

Are singleton beans thread‑safe?

Explain bean lifecycle in Spring

Important bean lifecycle methods and overriding them

What are internal beans in Spring?

How to inject a Java collection into Spring?

What is bean wiring?

What is autowiring?

Explain different autowiring modes

Limitations of autowiring

Can you inject null or empty string in Spring?

Java‑based Spring configuration examples

Annotation‑based container configuration

How to enable annotation wiring

@Required annotation

@Autowired annotation

@Qualifier annotation

How to use JDBC more effectively in Spring

JdbcTemplate

Spring’s support for DAO

How Spring integrates with Hibernate

Spring‑supported ORM

How to combine Spring and Hibernate via HibernateDaoSupport

Transaction management types supported by Spring

Advantages of Spring transaction management

Preferred transaction management type

Explain AOP

Aspect

Difference between concern and cross‑cutting concern in Spring AOP

Join point

Advice

Pointcut

What is introduction?

What is target object?

What is proxy?

Different types of automatic proxies

What is weaving and its variations?

XML‑based aspect implementation

Annotation‑based aspect implementation

What is Spring’s MVC framework?

DispatcherServlet

WebApplicationContext

Controller in Spring MVC

Kafka Interview Questions

How to get the list of topics

Producer and consumer command‑line tools

Is consumer push or pull?

How Kafka maintains consumer offset tracking

Explain master‑slave synchronization

Why a messaging system is needed; can MySQL replace it?

Role of Zookeeper in Kafka

Three transaction definitions for data transfer

Two conditions to determine if a Kafka node is alive

Three key differences between Kafka and traditional messaging systems

Three mechanisms of Kafka’s ACL

How to solve consumer dead‑lock issues

How to control consumer position

Ensuring ordered consumption in a distributed Kafka cluster

High‑availability mechanism of Kafka

How Kafka reduces data loss

How Kafka avoids duplicate consumption (e.g., for payment deduction)

Micro‑services Interview Questions

Understanding of micro‑services

Advantages of micro‑service architecture

Characteristics of micro‑services

Best practices for designing micro‑services

How micro‑service architecture works

Pros and cons of micro‑service architecture

Difference between monolith, SOA, and micro‑services

Challenges when using micro‑services

Difference between SOA and micro‑services

What is Domain‑Driven Design (DDD)?

Why DDD is needed

What is ubiquitous language?

What is cohesion?

What is coupling?

What is REST and its purpose?

Understanding of Spring Boot

What is Spring Boot’s executor?

What is Spring Cloud?

Problems solved by Spring Cloud

Purpose of @WebMvcTest in Spring MVC applications

Key points about testing micro‑services

Types of micro‑service testing

Understanding of distributed transactions

What is idempotence and where is it used?

What is a bounded context?

What is two‑factor authentication?

Credential types for two‑factor authentication

What is a client certificate?

Purpose of FACT in micro‑service architecture

What is OAuth?

What is Conway’s law?

What is contract testing?

What is end‑to‑end micro‑service testing?

Purpose of containers in micro‑services

What is DRY in micro‑service architecture?

What is consumer‑driven contract (CDC)?

Role of Web/RESTful APIs in micro‑services

Understanding of semantic monitoring in micro‑services

How to perform cross‑functional testing

How to eliminate nondeterminism in tests

Difference between mock and stub

Knowledge of Mike Cohn’s testing pyramid

Purpose of Docker

What is a canary release?

What is continuous integration (CI)?

What is continuous monitoring?

Role of an architect in micro‑service architecture

Can micro‑services be used to create state machines?

What is reactive scaling in micro‑services?