Prepare for next year's gold three silver four, this Java interview document summarized by Ali P8 boss, you must take a good look

Jump at the end of the year. Are you preparing to change jobs this year?

Ma Yun once said that there are many reasons for resignation. Only two points are true: 1. The money is not given in place; 2. The heart is wronged.

 

 

If you have already made a job-hopping plan, you must understand these considerations before choosing your next job.

Job hopping is a process that everyone has to go through in their career. Whether you searched for this article or accidentally browsed this article, I hope you did not waste your time here, and can give you the next or Later written interviews will bring some help.

2021  may be the best year of the Internet in the next 10 years. WINTER IS COMING. But if you don't really try it yourself, you never know what the market is like. After looking for a job this time, I feel that the market is not so terrible, and I also got offers from several major factories. Here is a summary, to myself, and hope to help the coders in need.

The editor has compiled a new interview review material for everyone, I hope I can help you~

Including: basic, collection framework, JVM, Java multithreading, MySQL, Redis, Spring, message queue, Dubbo, algorithms, design patterns, databases, network protocols, Linux systems, computer principles, etc. related knowledge points... and BATJ real Interview questions

Due to space limitations, it will be tedious to read too long, and it will also affect the reading experience. Instead of watching, it is better to get the document and refer to it slowly. Get original files and more resources

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This document provides a detailed catalog. You can choose your own weak knowledge for reference according to your actual needs.

Java basics

• The difference between overloading and rewriting
• What is the difference between String and StringBuffer and StringBuilder? Why is String immutable?
• Automatic boxing and unboxing
• Exception handling in Java
• What is the difference between interface and abstract class
• Common methods of Object class
• Get the two commonly used methods of keyboard input

Java basic interview topics and answers

Java Collection Framework

• Similarities and differences between Arraylist and LinkedList
• The difference between ArrayList and Vector
• The underlying implementation of HashMap
• The difference between HashMap and Hashtable
• Why is the length of HashMap a power of 2
• HashMap multi-threaded operation causes infinite loop problem
• The difference between HashSet and HashMap
• The difference between ConcurrentHashMap and Hashtable
• The specific implementation of ConcurrentHashMap thread safety/underlying specific implementation
• The underlying data structure of the collection framework

Collection framework interview topics and answers

Due to space limitations, I will not give examples one by one. It will be tedious to read too long and will also affect the reading experience. The following presentation will be shown in the form of pictures.

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In this part of multithreading, the interviewer is likely to ask you whether you have actually used multithreading in your project. So, if you have the experience of actually using Java multithreading in your project, it will give you a lot of points!

Java multithreading

• Talk about your understanding of the synchronized keyword
• Tell me how I use the synchronized keyword, is it used in the project?
• Talk about the underlying principle of the synchronized keyword
• Talk about what optimizations have been made at the bottom of the synchronized keyword after JDK1.6. Can you introduce these optimizations in detail?
• Talk about the difference between synchronized and ReenTrantLock
• Talk about the difference between the synchronized keyword and the volatile keyword
• Why use thread pool?
• Implement the difference between Runnable interface and Callable interface
• What is the difference between execute() method and submit() method?
• How to create a thread pool
• Introduce Atomic atomic class
• What are the 4 types of atomic classes in the JUC package?
• Talk about the use of AtomicInteger
• Can you give me a brief introduction to the principle of the AtomicInteger class

Multi-threaded interview topics and answers

The design goal of JVM is to provide a computer model based on abstract specification description, to provide very good flexibility for interpreter developers, and to ensure that Java code can run on any system that conforms to the specification. JVM provides specific definitions for certain aspects of its implementation, especially for the format of Java executable code, that is, bytecode (Bytecode). This specification includes the syntax and value of opcodes and operands, the numerical representation of identifiers, and the storage image of Java objects in Java class files and constant buffer pools in the JVM. These definitions provide JVM interpreter developers with the required information and development environment. The designers of Java hope to give developers the freedom to use Java as they wish.

JVM

• The memory model and partitions need to be detailed to what to put in each area.
• What are the GC collectors? Features of CMS collector and G1 collector.
• When do Minor GC and Full GC happen respectively?
• Partitions in the heap: Eden, survival (from + to), old age, their own characteristics.
• Briefly describe the java garbage collection mechanism?
• What are the methods of garbage collection in java?
• The class loader parent delegation model mechanism? What are class loaders and what are the class loaders?
• Briefly describe the java memory allocation and recovery strategy and Minor GC and Major GC

 

Network protocol

• The difference between TCP and UDP protocols
• Enter the URL address in the browser ->> The process of displaying the homepage
• The relationship between various protocols and HTTP protocol
• HTTP long connection, short connection
• TCP three handshake and four wave hands (frequent interviewer)

Network protocol interview topics and answers

MySQL is a relational database management system. Relational databases store data in different tables instead of putting all data in a large warehouse, which increases speed and flexibility.

The SQL language used by MySQL is the most commonly used standardized language for accessing databases. MySQL software adopts a dual authorization policy, divided into community version and commercial version. Due to its small size, high speed, low total cost of ownership, especially the characteristics of open source, the development of small and medium-sized websites generally chooses MySQL as the website database.

MySQL

• What are the technical characteristics of Mysql?
• Under what circumstances are MYSQL data tables easily damaged?
• Talk about my understanding of the two common storage engines of MySQL: MyISAM and InnoDB
• Do you understand database indexes?
• Can you tell me the basic storage structure of MySQL?
• How does Mysql add indexes to table fields?
• Talk about common optimization methods for large tables
• What field type is good for recording currency in mysql
• When the number of records in a single MySQL table is too large, the CRUD performance of the database will decrease significantly. What are the common optimization measures?

MySQL interview topics and answers

Simply put, redis is a database, but unlike traditional databases, redis data is stored in memory, so the storage and writing speed is very fast, so redis is widely used in the cache direction. In addition, redis is often used for distributed locks. Redis provides a variety of data types to support different business scenarios. In addition, redis supports transactions, persistence, LUA scripts, LRU-driven events, and multiple cluster solutions.

Redis

• Why use redis / why use cache?
• Why use redis instead of map/guava for caching?
• What is the difference between redis and memcached?
• The disadvantages of the Redis distributed lock mentioned above?
• Redis common data structure and usage scenario analysis
• Redis memory elimination mechanism (There are 2000w data in MySQL and only 20w data in Redis. How to ensure that the data in Redis are all hot data?)
• Redis persistence mechanism (how to ensure that the data can be recovered after redis hangs and restarts)?
• Solutions to cache avalanche and cache penetration problems?
• How to solve the key problem of concurrent competition in Redis?
• How to ensure data consistency between the cache and the database when it is double-written?

Redis interview topics and answers

Spring is generally inevitable. If your resume states that you know Spring Boot or Spring Cloud, then the interviewer may also ask you about these two technologies at the same time. For example, he may ask you the difference between springboot and spring. Therefore, you must be careful about what you write on your resume, and you must be very familiar with the things on your resume.

In addition, AOP implementation principle, dynamic proxy and static proxy, Spring IOC initialization process, IOC principle, how to implement an IOC container yourself? These things are often asked.

Spring

• What is the scope of Spring Bean?
• How to configure Spring based on Java configuration?
• Please tell me the life cycle of Spring Bean?
• What is the difference between the scope of Spring Bean?
• Please give an example of how to inject a Java Collection in Spring?
• What are the different types of events in the Spring framework?
• What design patterns are used in the Spring framework?
• What technologies are mainly used in the development of Spring?

Spring interview topics and answers

"RabbitMQ?" "Kafka?" "RocketMQ?"... In the daily learning and development process, we often hear the keyword message queue. This is also often asked in interviews

message queue

• What is a message queue?
• Why use message queues? What to do if the message is lost?
• How to solve the message duplication problem?
• Is the message retransmission interval and retransmission times in ActiveMQ?
• What if the ActiveMQ server is down?
• How to tune ActiveMQ?
• What is the usage of Basic.Reject?
• Why shouldn't you use a persistence mechanism for all messages?
• Why is disk node not recommended for heavy RPC usage scenarios?

Message queue interview topics and answers

Dubbo is open sourced by Ali and later joined Apache. Officially due to the appearance of Dubbo, more and more companies have begun to use and accept distributed architecture, so they are often asked during interviews

Dubbo

• What is Dubbo?
• What is RPC? What is the principle of RPC?
• Why use Dubbo?
• What is distributed? Why distributed?
• Let me first explain what load balancing is?
• What load balancing strategies does Dubbo cluster provide?
• What protocols does Dubbo support, the application scenarios of each protocol, the advantages and disadvantages?
• What are Dubbo's cluster fault tolerance solutions?
• The relationship between Dubbo and Spring Cloud?

Dubbo interview topics and answers

The data structure is more frequently asked: binary tree, red-black tree (it is very likely to let you draw a red-black tree out!), binary search tree (BST), balanced binary search tree (Self-balancing binary search tree), B-tree , Comparison of the advantages and disadvantages of B+ tree and B* tree, knowledge points of LSM tree.

Data structure is very important, and it is relatively difficult to learn. It is recommended that the learning of data structure must be done step by step, step by step. You must understand the principle, and it is best to use code to implement it yourself.

data structure

• What is a queue
• What is the type of queue
• What is Set? Talk about the underlying data structure of HashSet and TreeSet
• What is List? What are the common implementation classes of List?

Data structure interview topics and answers

In the Linux operating system, all resources managed by the operating system, such as network interface cards, disk drives, printers, input and output devices, ordinary files or directories, are regarded as one file.

In other words, there is an important concept in the LINUX system: everything is a file. In fact, this is a manifestation of the UNIX philosophy, and Linux is a rewrite of UNIX, so this concept has been passed down. In UNIX systems, all resources are regarded as files, including hardware devices. The UNIX system regards each hardware as a file, usually called a device file, so that users can access the hardware by reading and writing files.

 Linux

• Briefly introduce the Linux file system?
• Do you understand some common Linux commands?
• What are the main types of kernel locks in Linux?
• What is the meaning of user mode and kernel mode in Linux?
• What are the main ways of communication between user processes?
• What are the functions to apply for kernel memory through the partner system?
• Can module programs use linkable library functions?
• How does Linux implement system calls?
• What is the function of Linux soft interrupt and work queue?

Linux interview topics and answers

I personally feel that the interview is also like a brand new journey. Failure and victory are common things. Therefore, I advise you not to become discouraged and lose your fighting spirit because of the interview failure. Don't be complacent because you passed the interview. What awaits you is a better future, keep on!

Due to space limitations, the above interview topic answers are all organized in a pdf document. The detailed information in the document is too comprehensive, so only some of the knowledge points are screenshots for a rough introduction. Each small node has more detailed information. content!

How to obtain the compiled Java interview topic materials?

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BATJ real interview questions

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