Preface
Today, I would like to share with you the interview process of the fresh water friends on three sides of JD.com who won the Offer. At 20K, I thought it was the price of cabbage, and I was fainted!
One side (1 hour 30 minutes)
- Concept of class loading mechanism, loading steps, parent delegation mechanism, overall delegation mechanism, class loader types and inheritance relationships
- How to enable the class loader to load resource files on the network? How to customize the class loader? Does the custom loader still conform to the parent delegation mechanism? How to break the parent delegation mechanism?
- How many ways are there to instantiate objects?
- From the clone method of the Object class to the difference between deep copy and shallow copy
- The concept, usage, and practice of reflection
- Java memory model and JVM memory structure
- There is a 4-core 8G machine, how much memory should be allocated to the heap area and virtual machine stack in the JVM? (Initial value, maximum value, allocation ratio of young generation and old generation of heap area, etc.)
- What is the impact of too little or too much memory allocated by the young generation in the heap memory? Does copy count *** lead to Stop-the-World?
- Which parameters can set the memory allocation in the JVM?
- Need to share a variable in the thread scope, how to achieve it? How to avoid memory leaks caused by ThreadLocal source code implementation and Key weak references?
- The role, implementation mechanism, and cache consistency of volatile
- The role of AtomicInteger atomic class, source code implementation mechanism
- The CAS lock-free algorithm concept, source code implementation mechanism, and Unsafe source code are extended to the C++ method corresponding to the HotSpot virtual machine and then the corresponding assembly function
- The source code implementation of unfair lock in ReentrantLock, the AQS source code implementation, why do we need spin lock? The process of lock expansion?
- Thread pool usage scenarios, common parameters, rejection strategies
- Types of blocking queues, underlying data structure and usage scenarios
- Handwritten BIO Socket programming, the difference between BIO and NIO
- Netty thread model, zero copy, sticky package unpacking, heartbeat mechanism, Pipeline source code
- Principles in the responsibility chain model, strategy model, template model, and design model
- Top K problem, find the top 10 numbers from the largest to the smallest among tens of millions of numbers
- The difference between clustered index and sparse index in MySQL, is the more indexes the better? What kind of fields are suitable for indexing?
- The concept of index coverage and back to table, how to avoid back to table?
- Why use B+ tree instead of AVL tree?
- The underlying implementation of the transaction
- The concept and implementation mechanism of MVCC
- Why is Redis so fast? Why not use multithreading?
- The time complexity of the hash table query and the solution to the hash conflict?
- What are the application scenarios of Sorted Set, the implementation of jump tables, the time complexity of query and insertion?
- Dubbo's application scenarios, underlying communication components, service degradation, load balancing, interface exposure, serialization methods, let you implement a simple RPC framework, what would you do?
- Zookeeper's application scenarios, watch mechanism, leader election algorithm, ZK implementation of distributed locks
- Is the symmetric encryption, asymmetric encryption, digital certificate, HTTPS connection process, and SSL encryption necessarily safe? At what level does SSL implement encryption?
- OSI seven-layer protocol? Which layer does the router work on? Which layer does HTTP, TCP, FTP, DNS work?
- The role and process of ARP protocol
- Git operation and code conflict resolution
- Redis's solutions for cache penetration, cache avalanche, and data consistency
- Elasticsearch's inverted index, the concept of index and document, and the problem of split brain
- RabbitMQ application scenarios, production/consumer and publish/subscribe model concepts and applications, data loss issues
- The solution to oversold goods, MySQL optimistic locking and Redis optimistic locking
- Handwritten SQL: There is a table of results. There are three fields in the table: name, course, and grade. Find the name and average grade of students whose course average is greater than 85 points.
- Algorithm: Write merge sort and fast sort, analyze time complexity, how to evaluate whether it is a stable sorting algorithm?
Two sides (50 minutes)
- Hashmap和Concurrenthashmap
- Thread pool core parameters, rejection strategy
- Application scenarios of SynchroQueue? How many elements can be stored?
- How to implement Lock's fair lock and unfair lock
- Talk about AQS
- How does Lock allocate locks to threads?
- The life cycle of Spring Bean
- Talk about Spring's AOP
- Source code of SpringBoot startup process
- Netty zero copy? Heartbeat mechanism? Sticking and unpacking?
- How ASM implements cglib
- Talk about what indexes the database has? What is the difference between a clustered index and a non-clustered index? What is index coverage and back table? What is index pushdown?
- The difference between binary tree and B+ tree
- Know which common Linux commands
- What folders are in the Linux root directory
- Common JVM commands
- Common parameters of jstat
- Process communication method
- Linux thread scheduling method
- How many levels of Linux cache
- Redis delete strategy?
- What is distributed? What is the connection between distributed and microservices? Have you heard of CAP theory? Why does CAP theory satisfy two functions at most?
- Algorithm: Entrance of circular linked list
HR noodles (18 minutes)
- What do you think of the difficulty of the written test?
- I think your overall results in the previous rounds were quite high. Do you want to develop in Beijing in the future?
- There are many Internet companies in Guangzhou, Shenzhen and Hangzhou. Why did they invest in positions in Beijing?
- I may be more straightforward. Your academic qualifications are relatively low among our candidates. What do you think is your advantage?
- Ever thought of postgraduate entrance examination? If you don’t take the postgraduate entrance examination, do you think you are capable of these jobs in the next few years?
- Why do you think you didn't go to some better schools? Did you choose your major?
- How long is the internship? Give the interviewer an evaluation of the first two rounds?
to sum up
Finally, I learned that this water friend is a second undergraduate class in Guangdong, there is no competition, no project, the school has a college suffix, so far there is no school that interviewers have heard of, but I finally got an offer, so I hope this Friends' experience can help everyone, come on!
Finally, share the interview information with everyone for free, so that you can become the next boss!
Information collection: Click here to get it for free, password: CSDN
Love programming, love to share, I heard that those who like + follow have joined the big factory! ! !
