Face the summary - club resort - 6 years

​ This article lists the various difficulties faced by others,And where you can't,I haven't learned yet：Netty就跳过了

​ I feel that the core valuable point of the interview is in the project introduction,Different people have different projects,Still look at other people's projects,The non-items in the Mianjing can only be regarded as basic or intermediate knowledge.

参考链接：https://mp.weixin.qq.com/s/eqJ4mKdS69ADOCoB4035Fg

1.丰疆智能

1. ArrayList 的扩容机制：
   Initial creation does not define a length,第一次调用add定义为10,Subsequent expansion to the original1.5倍

2. HashMap 什么场景下是线程不安全的？会导致什么后果？
   jdk1.8之后put采用尾插法,Data will be overwritten under multi-threading

3. 当核心线程数未满,继续提交任务,是复用已经空闲的线程还是继续创建？
   继续创建,On the one hand, it is for thread warm-up,The number of core threads itself is the configured optimal value,On the other hand, threads have the overhead of competing for resource locks before multiplexing.

4. AQS 了解？里面都有哪些属性？AQS 有几种模式？你对 AQS 还有哪些理解？
   State,CLH.独占和共享(…见尚硅谷-JUC-AQS篇)

5. JVM 的内存模型？哪个区域不会发生 OOM？

​ [外链图片转存中…(img-srtbGtA0-1659345030120)]

2.西安移动研究院

1. 包装类是深拷贝还是浅拷贝？
   深拷贝.深拷贝：Make a fresh copy.浅拷贝：Only pointer references are copied,After modification, the original value is changed,IntegerThe bottom layer of the wrapper classfinal int ,就是深拷贝

2. Redis 的 key 删除策略？
   3种.定期删除（定时扫描）,定时删除（It will be deleted when the expiration time is up）,惰性删除（不处理,Use it and then judge whether to delete it）

3. 写代码时常见的内存泄漏？

   1. Long-lived references decorate short-lived references：static 引用 = 局部变量
   2. 数据库、文件IO、socketDisconnected without closing after connecting
   3. setAfter adding an object to the collection, modify the properties of the object and add it again(Modifying properties is modifyinghashcode)后.Repeatedly adding the original objecthashcode变更,Add in a new reference object,就会造成内存泄漏（…见尚硅谷-JVM-内存泄漏的8种情况）

4. 线程 A 中创建线程 B,线程 B 如何捕获线程 A 的异常？

   1. A thread is defined in a child thread,设置setUncaughtExceptionHandler.（You can find code experiments online）

5. 有哪些让线程阻塞的方法？有哪些类使用了 LockSupport？(Really good question)

   1. Object->wait,notify
   2. Condition->await,signal
   3. LockSupport->park,unpark.（AQSthe bottom isLockSupport阻塞线程,而AQSThe upper layer implementation isReentreenLock.lock, Future.get, CompletableFuture.get等这些,Their underlying code is used explicitlyLockSupport.park）

6. 泛型中 Extends 和 Super 关键字的区别？在 put 操作多时用哪种,为什么？在 get 操作多时用哪种,为什么

   1. <? extends T>是上界通配符,包含T和T子类,只能取数据,不能读
   2. <? super T>是下界通配符,包含T和T超类,只能存数据,不能取

7. SpringBoot 自动装配原理？

   1. SpringBootEach configuration class is automatically loaded on startup,Components are then loaded on demand（For details, see Shang Silicon Valley-SpringBoot-自动装配,Learning skipped before,Learn it later）

3.西安卓派

1. Spring 中的 ApplicationEvent 使用过？
   1. 事件监听,I didn't study because I didn't use it for a while.（尚硅谷-SpringAnnotation drivers are mentioned）
2. DDD 了解？是否知道其中的术语？
   1. domain-driven design领域驱动设计：It is to split a large requirement into problem domains,The problem domain is broken down into objects,Then consider the invocation and collaboration between the various problem domains.is compared to procedural programming、A reference link to the evolution of object-oriented programming：https://wenku.baidu.com/view/ea44f92393c69ec3d5bbfd0a79563c1ec4dad74e.html
3. HTTP 协议的无状态你怎么理解？无状态有啥好处和坏处？
   1. HTTPProtocols are stateless,This means that the server is unaware of the client state,2different requests to the server,服务器认为2This request has nothing to do with it.
   2. 相反,有状态就是cookie这种,The benefit is, of course, the saving of resources,The downside is that the server cannot log the user,This may be attacked by malicious frequent requests

4. 西安腾讯云

It is indeed Tencent,太难了.

1. 谈谈什么是零拷贝？
   1. 减少CPU复制次数.kafka（kafkaOne of the reasons for the speed：The system bottleneck is the networkIO,而0Copy is to reduce the number of memory copies）底层就是0拷贝.参考博客：https://blog.csdn.net/shenchaohao12321/article/details/115464117
   2. 感觉还是挺重要的,只学了个皮毛,A chapter will be devoted to studying it later.
2. 一共有几种 IO 模型？NIO 和多路复用的区别？
   1. Make up later,IOThis piece is really too fake.
   2. 参考链接：https://blog.csdn.net/lzb348110175/article/details/98941378
3. TCP 怎么实现拥塞控制？怎么实现重传（说了思路不过具体的实现回答的不准确）？
   1. 慢开始,拥塞避免,快重传,快回复（难受啊,大学学的408Forgot all about it,The notes made are gone）
   2. 参考链接：https://blog.csdn.net/qq_46312987/article/details/124061775

5. 翼支付

1. HashMap 如何减少 hash 碰撞;
   1. 线性探测法：A local conflict,Search backwards in linear order.ThreadLocalThat's the way
   2. 链式寻址法：If there is a conflict, add it to the back of the linked list.HashMap, HashTable
   3. 再Hash：hash之后hash
   4. 公共溢出区：hashTables are divided into base tables and overflow tables,Conflicting elements are placed in the overflow table
2. Redis 热 Key 如何解决
   1. 热KeyJust multiple requests for accessRedis上同一个key,Make it a cluster