After 4 rounds and 2 hours, finally cut meituan offer!

• I focused on the single example 、 Factory method 、 agent

• 《 A big factory Java Analysis of interview questions + Back end development learning notes + The latest architecture explanation video + Practical project source code handout 》 Open source
    I don't know , No nonsense , Just say you don't know

• Actually, I don't want to be asked Spring In detail , I didn't review the frame, and I don't remember much . So I said to the interviewer Spring Some of the more important mechanisms I understand are not bad , Then I use a practical example to show that I am right IOC、AOP I've explained for a moment , He was right , Good understanding （ It's hard to meet an interviewer who can give feedback while interviewing , So happy ）

• Here I'll focus on Synchronized keyword , There are also some locks under the contract , And their advantages and disadvantages and differences .volatile Keywords I mainly from visibility 、 Atomicity and prohibition JVM There are three aspects of reordering , Let's talk about my single instance mode in multithreading double-check It is used in volatile Keywords prohibit JVM Instruction rearrangement optimization .

• From dispatch 、 concurrency 、 Resources and overhead .

• Java IO It's synchronous blocking , How does it implement synchronous blocking . I took read() Method, for example .NIO It is synchronous and non blocking , I told you more about Selector Medium select() Method polling shows how it implements multiplexing IO Of . Then I compared their efficiency . The interviewer may see that I have a better understanding of this area , Continue to ask me Java Is asynchrony implemented in IO, I don't feel like , But the interviewer said there was , Let me see , Actually, I don't know , So I told the interviewer that I was right Unix Medium asynchrony IO Understanding of the model , Then as for Java I really don't know if there is any in it .（ He actually smiled ！ It's right to say you understand ,Java It doesn't matter if there's any in it ！ ha-ha ）

• I just use some of the front end js nothing more , Used to jquery frame , Ask me Ajax What is the full name , I guess it's asynchronous  
  Java Open source project 【ali1024.coding.net/public/P7/Java/git】
   js and xml.Ajax In fact, I don't understand the principle of realization , I'll just talk about how it passes XMLHttpRequest Object to query asynchronously ,Ajax The engine runs on the client side , Reduced server workload .

• Because my resume says that I'm on Multithreading 、 Concurrency is a better understanding . So he's always asking questions about this . This problem is because I have seen ThreadPoolExecutor Source code , So I'm going to follow that kind of design thinking , Let's talk about the core pool in detail 、 Creating threads can be designed using the factory method pattern 、 Thread pool state 、 Blocking queues 、 These aspects of rejection strategy . The design is quite comprehensive .

• The singleton pattern ,jdk Medium getRuntime(); Factory method model ,ThreadPoolExcutor be used ThreadFactory; Observer mode ：java.util Under the bag Observable and Observer. Finally, it mainly talks about the use scenario of factory method pattern .

• I talk about database design optimization and query optimization . Indexes B+ Tree implementation ,InnoDB and MyISAM The implementation difference of primary key index , One gathering one non gathering .

• Four levels of isolation , What are the possible exceptions ,mysql Default level in .

• I said this undergraduate course has learned , But it didn't work for a long time , I forgot all the orders . He said it was OK , Test you a few simple ：cd、ls、dir（ It's really simple ）

• from 10 The smallest of ten thousand 10 individual , Time complexity analysis （ The biggest pile , Think about memory ）

• Find the maximum sum of successive subarrays from a positive and negative array , Time complexity analysis （ Dynamic programming ）

• Full of two branches i How many nodes does the layer have ,n How many nodes does the full binary tree of the layer have

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