2021 latest sharing summary of Alipay/Meituan/Pinduoduo

The author graduated in 2014 and worked in Shanghai. He has been engaged in Java research and development for more than five years. He changed jobs twice in the middle. The salary is still satisfactory. However, the work content is repeated wheeling, technical improvement is slow, and I feel that I can't learn anything. I have always dreamed that one day I can work in large Internet companies such as BAT, learn from Daniel, improve my technical capabilities, and gild my resume.

From the day when this idea came up, I began to pay close attention to the recruitment information of Java posts of major Internet companies, as well as to sort out various technical dry goods, face-to-face questions, etc., through combing and summarizing, checking for omissions and filling vacancies, and doing according to my own situation. A detailed study plan was made to make up for the short version of their technical knowledge. At the end of the article, some faces are free to share!

Alipay interview

 

Alipay side

1. Introduce yourself.
2. What are the core designs involved in the project
3. ArrayList and LinkedList bottom layer
4. HashMap and thread-safe ConcurrentHashMap, and their advantages and disadvantages
5. How to achieve thread safety in Java
6. Which is better, Synchronized or Lock?
7. How is the get() method in HashMap implemented?
8. What scenarios can HashMap be used in?
9. JVM, garbage collection mechanism, memory division, etc.
10. SQL optimization, commonly used indexes?
11. What more questions need to be asked.

02 Alipay two sides

1. Without self-introduction, I just asked which Java development-related projects I have done.
2. Which technologies are you familiar with?
3. Multi-threaded state diagram, how does the state flow?
4. Deadlock, the cause of the deadlock
5. Page lock, optimistic lock, pessimistic lock?
6. How does optimistic locking ensure thread safety?
7. Have you used the thread pool, the corresponding benefits, how to use it?
8. Two 10G files contain some URLs and the memory is only 1G. How to merge these two files to find the same URL?
9. More than 1000 concurrent threads, 10 machines, each machine has 4 cores, and the thread pool size is designed.
10. Code question: Two ordered arrays, there are duplicate numbers in the array, merge them into an ordered array, and remove the duplicate numbers.
11. Talk about your strengths.

Alipay three sides

1. What has been done in jvm performance tuning
2. How to do database performance tuning
3. Principles of distributed systems: CAP, eventual consistency, idempotent operations, etc.
4. Under high concurrency, how does our system support a large number of requests?
5. How the cluster synchronizes session state
6. Commonly used NOSQL, have you made a comparison?
7. Under what circumstances will avalanches occur, and how to deal with them?
8. Principles of load balancing
9. Database transaction attributes
10. When communicating with colleagues, how to resolve conflicts?
11. What do you feel lacking in your work?
12. Do you have any questions?
13. Expect salary?
14. Why leave the current company?

Meituan

 

Meituan Dianping's advanced Java side (technical, telephone interview, about 40 minutes)

1. Self introduction.
2. Project Introduction.
3. Have you understood the redis source code and redis cluster?
4. How does redis guarantee thread safety in distributed mode?
5. The principle of Hashmap, source code?
6. How does the back-end data structure shift in the case of Hashmap additions and deletions?
7. Why is the hashmap capacity a power of 2?
8. Do you know the method of the object class?
9. Have you rewritten hashcode and equals, what should you pay attention to?
10. JVM memory partition, why should there be a new generation and an old generation?
11. Is there a JVM memory optimization?
12. What is the difference between a database index primary key and a unique index?
13. The difference between clustered index and non-clustered index?
14. The difference between MySQL storage engine innoDB and MyISAM?
15. Tell me about the stable sorting algorithm and the unstable sorting algorithm?
16. Tell me about the idea of ​​quick sort?

Meituan Dianping Advanced Java Second Side (technical, on-site interview, about 60 minutes)

1. What are the differences between several thread pools?
2. Understanding of aio, nio and bio, what are the core concepts of NIO?
3. What are the commonly used NIO frameworks, their advantages and disadvantages?
4. The four isolation levels of transactions?
5. Jvm scene problem, memory fragmentation occurs in the old generation after the mark is cleared many times, causing full gc. What problems might happen next?
6. What is the difference between MySQL innodb's b+ tree index, primary key index, and clustered index?
7. Four major characteristics of the database?
8. What kind of locks, row locks, table locks, and optimistic locks are there in MySQL?
9. Here are two examples of how MySQL's deadlock occurs.
10. What does the zookeeper in dubbo do?
11. Table lock, row lock, optimistic lock, pessimistic lock, characteristics and differences?
12. What are the concurrency toolkits and how to use them?
13. How is Docker usually used?
14. How does Kafka solve data accumulation?
15. Kafka message storage mechanism?
16. How to use Kafka to ensure the orderliness of messages?
17. How does Kafka ensure that messages are only consumed once under concurrent conditions?

Meituan Dianping Advanced Java three-sided questions (technical, on-site interview, about 60 minutes)

1. Project Introduction.
2. For the most technically difficult projects, introduce the relevant core design process.
3. How does redis guarantee thread safety in distributed mode?
4. The way and difference of redis persistence?
5. How does zookeeper implement distributed locks and how to implement other distributed locks?
6. Kafka's architecture, how to use Kafka to ensure the orderliness of messages?
7. What does the optimization of the database include? MySQL optimization, talk about two examples of your optimization.
8. Which version of redis is used?
9. How to build a redis cluster?
10. How does redis master-slave synchronization?
11. Precautions for redis distributed locks?
12. The way and difference of redis persistence?
13. Redis persistence method and difference?
14. What is the amount of data in my sql that needs to be divided into tables?
15. What storage engines are commonly used in my sql and their differences?
16. The role of zookeeper: distributed lock, registration service center?
17. How does zookeeper implement distributed locks and how to implement other distributed locks?
18. Solutions for distributed transactions?
19. How to achieve single sign-on?
20. How to realize the spike system?
21. At work, if you encounter a technical bottleneck that cannot be solved, what is your solution?
22. In terms of technology selection, how would you choose between a new technology and a stable old technology, and what factors would you consider?

Meituan Dianping Advanced Java Four-sided Questions (HR, on-site interview, about 30 minutes)

1. Introduce yourself.
2. Own strengths and weaknesses.
3. Why do you want to come to Meituan and how much do you know about Meituan?
4. Sort of Internet companies in mind.
5. How did you deal with problems that could not be solved temporarily at work?
6. What new technology are you learning recently
7. What path and method did you use to learn and get in touch with a new technology?
8. What is your future career plan?

Pinduoduo Java R&D Post 4 Interview and Interview Questions

 

one side

1. What are the components of the thread pool, what thread pools are there, how to use them, and what are the rejection strategies
2. Write an algorithm to traverse the tree level and output the level of each level
3. Write a question, post-order traversal of binary tree, non-recursive algorithm.
4. When does a deadlock occur in multiple threads, write an example
5. Talk about the optimization of hashMap and the optimization of concurrentHashMap in jdk1.8
6. How to resolve the hash conflict, and if there is a conflict, how to find the target value in the hash table
7. There are 1000 data stored in the hashmap, what is the actual number, considering the load factor and expansion
8. What are the common RPCs? Corresponding difference and performance comparison?
9. Operating system's user mode and core mode switching conditions and why they need to be switched
10. Communication method between threads, asynchronous queue, delayed message acquisition

Two sides

1. How to do MySQL master-slave replication
2. MySQL index, the benefits of using B+ tree index
3. MySQL performance view and how to optimize
4. How does Redis cache
5. Redis persistence operation
6. How to use redis to process hot data
7. The TCP three-way handshake process, if there is no third handshake, what is the problem.
8. How to implement distributed locks

Three sides

1. Do you understand cap, what do you mean?
2. Network programming nio and netty related, netty thread model, zero copy implementation
3. Is Redis single-threaded or multi-threaded? How to do Redis distributed cluster?
4. What are the distributed message queues (Kafka, etc.)? Which ones have you used? What specific application scenarios?
5. How do you do load balancing, why do you do it? Have you ever learned about cluster avalanches?
6. Talk about the realization of peak shaving and current limiting in high concurrency scenarios?

Four sides (HR)

1. Why quit?
2. What is the expected salary?
3. How to treat the problem of overtime?
4. How do you usually learn technology, besides Java-related, what other technologies will you learn about?
5. What are the plans for the next few years?

At the end of the interview, check for missing and fill vacancies

Every interview is an opportunity to test your knowledge and technical strength. After the interview, it is recommended that you summarize and review in a timely manner, check for omissions, and then study in a targeted manner. This can not only increase the probability of success in the next interview, but also Increasing your own technical knowledge stack can be described as killing two birds with one stone.

The following is the latest summary of the scope and answers of Ali P6 senior Java required exam questions and answers , including the most comprehensive MySQL, Redis, Java concurrent programming, etc. interview questions and answers, for reference~

Data collection method: forward + forward + forward and follow after you click on the portal ! !

 

 

More notes to share