Interview question sharing: Section 1 of the most complete Java interview questions in 2018!

A few days ago, some friends in the exchange group asked questions related to the interview. At that time, they gave some questions. I was too tired to type. I didn’t write it down, but I thought it was a very irresponsible performance, so I sorted it out. Private collections in recent years, I would like to share them with you!

This set of interview questions is suitable for interviews at all stages of Java development, but it is more biased towards junior and intermediate developers! Since the answer to each question is not unique and the answer can be found on the Internet, only the question is given here, and the reference answer is not listed.

1. Basics

1.1, Java basics

Object-Oriented Traits: Inheritance, Encapsulation, and Polymorphism
The difference between final, finally, finalize
What are the similarities and differences between Exception, Error, runtime exception and general exception
Please write 5 common runtime exceptions
What is the difference between int and Integer, the value cache range of Integer
Packing classes, boxing and unboxing
String、StringBuilder、StringBuffer
The difference between overloading and overriding
What is the difference between abstract class and interface
Talk about the use and implementation of reflection
Talk about the scene and implementation of custom annotations
The difference between GET and POST methods of HTTP requests
Difference between Session and Cookie
List your commonly used JDK packages
MVC design thinking
Difference between equals and ==
The difference and connection between hashCode and equals methods
What is Java serialization and deserialization and how to implement Java serialization? Or please explain what the Serializable interface does
Common methods in the Object class, why wait notify is placed in Object?
How Java's platform independence manifests itself
Difference between JDK and JRE
What's new in Java 8

1.2, Java common collection

Difference between List and Set
The connection between Set and hashCode and equals method
Difference between List and Map
Difference between Arraylist and LinkedList
Difference between ArrayList and Vector
Difference between HashMap and Hashtable
Difference between HashSet and HashMap
The difference between HashMap and ConcurrentHashMap
The working principle and code implementation of HashMap, when to use the red-black tree
The problem of HashMap infinite loop in the case of multi-threading
HashMap has the problem of Hash DOS attack
The working principle and code implementation of ConcurrentHashMap, how to count the number of all elements
Handwritten simple HashMap
Have seen the source code of those Java collection classes

1.3. Processes and threads

The concepts of threads and processes, the concepts of parallelism and concurrency
How to create a thread and its implementation
How to communicate between processes
Talk about the principle and difference between CountDownLatch and CyclicBarrier
Talk about the Semaphore principle
Talk about the principle of Exchanger
Analysis of the principle of ThreadLocal, why does OOM appear in ThreadLocal, and the underlying principle
Talk about the implementation principle of thread pool
Several implementations of thread pools
The life cycle of the thread, how the state is transferred
Reference: " Java Multithreaded Programming Core Technology "

1.4, lock mechanism

Talk about thread safety, what is thread safety, how to ensure thread safety
The concept of reentrant locks, why can reentrant locks prevent deadlocks
Four conditions for deadlock (mutual exclusion, request and hold, no preemption, circular wait)
How to check for deadlock (check deadlock via jConsole)
volatile implementation principle (forbid instruction rearrangement, refresh memory)
Synchronized implementation principle (object monitor)
The difference between synchronized and lock
AQS synchronization queue
CAS lock-free concept, optimistic locking and pessimistic locking
Common atomic operation classes
What is the ABA problem and how does the JDK solve the ABA problem
Business scenarios and implementation methods of optimistic locking
Common concurrency classes under the Java 8 parallel package
The concept of bias lock, lightweight lock, heavyweight lock, spin lock
Reference: " Java Multithreaded Programming Core Technology "

1.5、JVM

JVM runtime memory area division
Examples and causes of memory overflow OOM and stack overflow SOE, how to troubleshoot and solve them
How to tell if an object is recyclable or alive
Common GC recovery algorithms and their meanings
Common JVM performance monitoring and troubleshooting tools: jps, jstat, jmap, jinfo, jconsole, etc.
How JVM sets parameters
JVM performance tuning
Class loaders, the parent delegation model, the life cycle of a class, how classes are loaded into the JVM
The process of class loading: loading, verification, preparation, parsing, initialization
Strong reference, soft reference, weak reference, phantom reference
Java Memory Model JMM

1.6. Design Patterns

common design patterns
The Six Principles of Design Patterns and Their Meanings
Common singleton patterns and the advantages and disadvantages of various implementations, which one is the best, handwritten common simple interest patterns
Application of Design Patterns in Actual Scenarios
What design patterns are used in Spring
What design patterns are used in MyBatis
What design patterns are used in your project
Talk about the analysis of the use of design patterns in common open source frameworks
Dynamic proxies are important! ! !

1.7, data structure

Trees (binary search trees, balanced binary trees, red-black trees, B-trees, B+ trees)
Depth-limited algorithm, breadth-first algorithm
Kruskal's Algorithm, Prinmo's Algorithm, Diclas' Algorithm
What is consistent Hash and its principle, Hash ring problem
Common sorting algorithms and search algorithms: quick sort, halved search, heap sort, etc.

1. 8. Network/IO Basics

Concepts of BIO, NIO, and AIO
What are long and short connections
What is the difference between Http1.0 and 2.0, please refer to " Http 2.0 "
Basic Concepts of HTTPS
Three handshakes and four waves, why do you need four waves
What happens from entering the URL in the browser until the page loads? Refer to " What Happens From Entering URL to Page Loading "

2. Data storage and message queue

2.1. Database

Notes on using MySQL indexes
What do DDL, DML, and DCL refer to?
explain command
left join，right join，inner join
Database Transaction ACID (Atomicity, Consistency, Isolation, Durability)
The isolation level of the transaction (read uncommitted, read committed, repeatable read, serializable read)
Dirty reads, phantom reads, non-repeatable reads
Several paradigms of the database
Common database commands
Talk about sub-library and sub-table design
Distributed dilemma and countermeasures brought by sub-database and sub-table (how to solve sub-database and sub-table under distributed, global table?)
Talk about SQL optimization
Deadlock problems encountered by MySQL, how to troubleshoot and solve them
The difference between the storage engine InnoDB and MyISAM, advantages and disadvantages, usage scenarios
Index category (B+ tree index, full-text index, hash index), the principle of index
What is Adaptive Hash Index (AHI)
Why use B+tree as the data structure of MySQL index
Difference between clustered index and non-clustered index
Have you ever encountered an index failure, when might it appear, and how to solve it
limit 20000 loading is very slow how to solve
How to choose a suitable distributed primary key scheme
Choose the right data storage solution
Several common distributed ID design schemes
Common database optimization solutions, how to optimize the database in your project

2.2、Redis

What data types does Redis have, please refer to " Detailed Explanation of 5 Different Data Types Common in Redis "
Redis internal structure
Redis usage scenarios
Redis persistence mechanism, please refer to " Using Snapshots and AOF to Persist Redis Data to Hard Disk "
Redis cluster scheme and implementation
Why is Redis single-threaded?
Cache Avalanche, Cache Penetration, Cache Warmup, Cache Update, Cache Downgrade
Reasonableness of using cache
Redis common recycling strategies

2.3, message queue

Usage scenarios for message queues
Message retransmission compensation solution
The idempotent solution of messages
message stacking solution
How to implement a message queue yourself
How to ensure the order of messages

3. Open source frameworks and containers

3.1、SSM/Servlet

Servlet life cycle
The difference between forwarding and redirecting
What is the difference between BeanFactory and ApplicationContext
Spring Bean life cycle
How Spring IOC is implemented
The scope of beans in Spring, which is the default
Talk about the implementation principle of Spring AOP and Spring AOP
Dynamic proxy (CGLib and JDK), advantages and disadvantages, performance comparison, how to choose
Spring transaction implementation, transaction propagation mechanism, default transaction category
The underlying principle of Spring transaction
Spring transaction failure (transaction nesting), the pit buried by JDK dynamic proxy for Spring transaction, please refer to "The pit buried by JDK dynamic proxy for Spring transaction! 》
How to customize the annotation implementation function
Spring MVC running process
Spring MVC startup process
Spring's singleton implementation principle
What design patterns are used in the Spring framework
Spring other products (Srping Boot, Spring Cloud, Spring Security, Spring Data, Spring AMQP, etc.)
Have you used Spring Boot? The understanding and principle of Spring Boot
The principle of MyBatis
Refer to " Why Spring "
Refer to " Why Spring AOP "

3.2、Netty

Why choose Netty
Talk about the usage scenarios of Netty in business
Native NIO has an epoll bug in JDK 1.7
What is TCP sticking/unpacking
The solution to TCP sticking/unpacking
Netty threading model
Talk about Netty's zero copy
Netty internal execution process
Netty reconnection implementation

3.3、Tomcat

Tomcat's infrastructure (Server, Service, Connector, Container)
How Tomcat loads servlets
Pipeline-Valve mechanism
Can refer to: " Four pictures take you to understand the Tomcat system architecture ! 》

4. Distributed

4.1、Nginx

Please explain what is C10K problem or know what is C10K problem?
For an introduction to Nginx, please refer to " Introduction to Nginx "
Forward proxy and reverse proxy.
Several common load balancing strategies for Nginx
What are the Master and Worker processes on the Nginx server?
What are the advantages of using a "reverse proxy server"?

4.2. Distributed others

Talk about the use of distributed scenarios in business
Session distributed solution
Session distributed processing
Application scenarios of distributed locks, causes of distributed locks, and basic concepts
Distribution is a common solution to locks
Common Solutions for Distributed Transactions
Algorithms and Implementations of Clustering and Load Balancing
To talk about the design of sub-database and sub-table, please refer to " Specific Implementation Plan of Database Sub-database and Sub-table Strategy "
Distributed dilemma and countermeasures brought by sub-database and sub-table

4.3、Dubbo

What is Dubbo, please refer to " Introduction to Dubbo "
What is RPC, how to implement RPC, and the implementation principle of RPC, please refer to " RPC Implementation Based on HTTP "
What is the concept of SPI in Dubbo
The basic principle and execution process of Dubbo

5. Microservices

5.1. Microservices

How is the front-end and back-end separation done?
Which frameworks are microservices
What are the common components of Spring Could? Refer to " Spring Cloud Overview "
Do you understand domain-driven? What is Domain Driven Model? Congestion model, anemia model
Do you know about JWT? What is JWT? Please refer to "JWT of Front-End Separation Tool "
How do you understand RESTful
Talk about how to design a good API
How to understand the idempotency of RESTful APIs
How to ensure the idempotency of interfaces
Talk about CAP theorem and BASE theory
How to Consider Data Consistency
Talk about the implementation of eventual consistency
For the advantages and disadvantages of microservices, please refer to " Microservice Criticism "
Difference Between Microservices and SOA
How to split services, split horizontally, split vertically
How to deal with chain call exceptions of microservices
How to fast track and locate problems
How to ensure the security and authentication of microservices

5.2, security issues

How to prevent common web attacks and SQL injection
Server communication security attack and defense
Analysis of HTTPS principle, downgrade attack, comparison of HTTP and HTTPS

5.3, performance optimization

What are the performance indicators
How to spot performance bottlenecks
Common means of performance tuning
Talk about how you perform performance tuning in your project

6. Others

6.1. Design ability

Tell us about the UML diagrams you have used in your project
How do you think about componentization, serviceization, and system splitting?
How to design a spike scene
Please refer to: " Seckill System Technical Challenges, Coping Strategies and Architecture Design Summary 1 or 2! 》

6.2. Business engineering

Talk about your development process and how to automate deployment
How you communicate with your team
How do you conduct code reviews
Tell us about your understanding of technology and business
Talk about the most difficult bug you encountered in the project and how to solve it
Introduce a project in your work that you think is the most valuable, as well as your role in the process, the problems solved, and what you think your project is lacking

6.3. Soft power

Tell us about your strengths and weaknesses
Tell me what book, what blog, what new technology you are researching recently, and then look at the source code of those open source projects
Tell me about the technical books you find most meaningful
What do you do in your spare time, how do you usually study, and how do you improve your abilities?
Discuss about the direction of personal development
Tell us what skills you think a server developer should have
Tell us what you think an architect is like and what an architect mainly does
How to deal with overtime
Welcome to leave a message to discuss the above problems! What are the frequently asked interview questions are also welcome to leave a message to add!

If you feel that you have something to gain, you can click on the collection and forward it. I specially organized it. There are many questions that cannot be explained clearly in a few words, so I simply asked a friend to record some videos to answer these interview questions. The answers to many questions are actually very simple, but the thinking and logic behind them are not simple. If you want to get these videos, you can add my Java architecture group: 725633148 , there are Ali Daniel in the group, and there are various Java distributed, JVM, multi-threading and other technical videos to share with you for free.

There will be updates in the future, so stay tuned!