HashMap source code interview analysis

itread01 2020-11-06 01:23:33
hashmap source code interview analysis


####HashMap Source code problem analysis 1. ** Ask : Say yes hash The understanding of the ** answer : hash Is for any length of input and output for the same length of output 2. Ask : hash The problem of algorithm answer : hash Conflict issues 3. Ask : hash Whether conflict can be avoided answer : It can't be avoided , Only try to avoid 4. ** Ask : Excellent hash What are the features of the algorithm ** answer : 1. Any small change hash The results are different 2. hash Irreversible 3. Long strings of hash Be efficient 4. hash The values are as good as possible 5. The same value hash Same value 5. ** Ask : hashmap Data structure of ** answer : With 1.8 For example Array + Link string + Red and black trees Data is stored in node In objects ,node There is key value next hash Wait for the field 6. Ask : How long is the initial length of the hash table answer : The default is 16 7. Ask : When was the hash table created answer : for the first time put It's time to build ( Lazy loading ) 8. Ask : What is the default load factor , Load factor of action answer : The empty parameter structure establishes hashmap The load factor of is 0.75, It works when node The number is larger than the array length 0.75 When it comes to resize Expansion 9. ** Ask : What conditions are needed to convert a red black tree into a concatenated one ** answer : Two conditions are needed The length of the linked string is greater than or equal to 7 And the length of the array is greater than or equal to 64 Before treeing 10. ** Ask node Of objects hash How to get the value , Why do you do this ** answer : It's based on key Of hashcode The value is in relation to key Of hashcode The height of 16 A bit exclusive or operation , It's for more random and uniform distribution in the array , Because hashmap The method of calculating array subscript is (tab.length-1)&hash,tab.length Less than in most cases 2^16 That is to say 25536( The rules say tab.length It has to be 2 To the power of ) So most of the time it's hash It's low 16 Bits are involved in operations , In order to make hash More random and even , One more time with key Of hashcode To enforce by XOR hash Random distribution of values , Let hashcode No one is involved in the operation 11. Ask : **hashmap put The detailed process of the method ** answer : key After addressing, we find the subscript in the array 1. If the array subscript is null Deposit directly into node 2. If not empty, compare the values Same coverage If it is a tree, put it according to the rules of red and black trees If it's not a tree The length of the concatenation is greater than or equal to 7 And the array length is larger than 64 Turn the tree The length exceeds the threshold resize 12. Ask : The principles of red and black trees answer : 1. The path from leaf node to root node has the same number of black nodes ( Black high ) 2. The leaf nodes are all black 3. You can't have two red nodes connected 4. The root node must be black 5. The inserted node must be red ( Red plug ) 13. Ask : jdk1.8hashmap Why the introduction of red and black trees answer : Because if the link string is too long, the query efficiency will be reduced hash The aim is to achieve as much as possible o(1) Of , Link addressing is slow 14. Ask : hashmap When will the expansion be triggered answer : put When operating , There is a field to record the expansion when the data volume is greater than the expansion threshold 15. Ask : hashmap How to expand answer : The array length must be 2 To the power of , Each expansion is to shift the original length to the left by one bit <<1 16. ** Ask : How to migrate the data from the old array to the new array ** answer : 1. hash If there is no conflict, it can be put in according to the new array length 2. If it has become a red and black tree 3. It's not a tree Association hash& Old array length (oldcap) Equal to 0 Lower the chain of It's not the same as raising the chain Low chain put the original index The original high chain index+oldlength The location of Explain : stay hashmap The addressing algorithm calculates that (hash&(length-1)) The data in a linked column is bound to be divided into two linked Columns Position one is the original index The other is yuan index+oldlength The original length The length is 16 The binary system is 10000 So length Namely 16-1 =15(1111) Namely hash&1111 By the end of 15 A bucket, for example , So hash The value of may be 01111 perhaps 11111 After expansion length It becomes 32 The binary system is 100000 hash&11111 So if 15 This bucket was originally hash yes 01111 Of node Just put it in his original 15 This position of ,hash For 11111 It's in 32 The position of the barrel 01111 & 10000 = 0 This one puts 15 This position 11111 & 10000 != 0 discharge 32 15+16 = 31 This person
版权声明
本文为[itread01]所创,转载请带上原文链接,感谢

  1. 【计算机网络 12(1),尚学堂马士兵Java视频教程
  2. 【程序猿历程,史上最全的Java面试题集锦在这里
  3. 【程序猿历程(1),Javaweb视频教程百度云
  4. Notes on MySQL 45 lectures (1-7)
  5. [computer network 12 (1), Shang Xuetang Ma soldier java video tutorial
  6. The most complete collection of Java interview questions in history is here
  7. [process of program ape (1), JavaWeb video tutorial, baidu cloud
  8. Notes on MySQL 45 lectures (1-7)
  9. 精进 Spring Boot 03:Spring Boot 的配置文件和配置管理,以及用三种方式读取配置文件
  10. Refined spring boot 03: spring boot configuration files and configuration management, and reading configuration files in three ways
  11. 精进 Spring Boot 03:Spring Boot 的配置文件和配置管理,以及用三种方式读取配置文件
  12. Refined spring boot 03: spring boot configuration files and configuration management, and reading configuration files in three ways
  13. 【递归,Java传智播客笔记
  14. [recursion, Java intelligence podcast notes
  15. [adhere to painting for 386 days] the beginning of spring of 24 solar terms
  16. K8S系列第八篇(Service、EndPoints以及高可用kubeadm部署)
  17. K8s Series Part 8 (service, endpoints and high availability kubeadm deployment)
  18. 【重识 HTML (3),350道Java面试真题分享
  19. 【重识 HTML (2),Java并发编程必会的多线程你竟然还不会
  20. 【重识 HTML (1),二本Java小菜鸟4面字节跳动被秒成渣渣
  21. [re recognize HTML (3) and share 350 real Java interview questions
  22. [re recognize HTML (2). Multithreading is a must for Java Concurrent Programming. How dare you not
  23. [re recognize HTML (1), two Java rookies' 4-sided bytes beat and become slag in seconds
  24. 造轮子系列之RPC 1:如何从零开始开发RPC框架
  25. RPC 1: how to develop RPC framework from scratch
  26. 造轮子系列之RPC 1:如何从零开始开发RPC框架
  27. RPC 1: how to develop RPC framework from scratch
  28. 一次性捋清楚吧,对乱糟糟的,Spring事务扩展机制
  29. 一文彻底弄懂如何选择抽象类还是接口,连续四年百度Java岗必问面试题
  30. Redis常用命令
  31. 一双拖鞋引发的血案,狂神说Java系列笔记
  32. 一、mysql基础安装
  33. 一位程序员的独白:尽管我一生坎坷,Java框架面试基础
  34. Clear it all at once. For the messy, spring transaction extension mechanism
  35. A thorough understanding of how to choose abstract classes or interfaces, baidu Java post must ask interview questions for four consecutive years
  36. Redis common commands
  37. A pair of slippers triggered the murder, crazy God said java series notes
  38. 1、 MySQL basic installation
  39. Monologue of a programmer: despite my ups and downs in my life, Java framework is the foundation of interview
  40. 【大厂面试】三面三问Spring循环依赖,请一定要把这篇看完(建议收藏)
  41. 一线互联网企业中,springboot入门项目
  42. 一篇文带你入门SSM框架Spring开发,帮你快速拿Offer
  43. 【面试资料】Java全集、微服务、大数据、数据结构与算法、机器学习知识最全总结,283页pdf
  44. 【leetcode刷题】24.数组中重复的数字——Java版
  45. 【leetcode刷题】23.对称二叉树——Java版
  46. 【leetcode刷题】22.二叉树的中序遍历——Java版
  47. 【leetcode刷题】21.三数之和——Java版
  48. 【leetcode刷题】20.最长回文子串——Java版
  49. 【leetcode刷题】19.回文链表——Java版
  50. 【leetcode刷题】18.反转链表——Java版
  51. 【leetcode刷题】17.相交链表——Java&python版
  52. 【leetcode刷题】16.环形链表——Java版
  53. 【leetcode刷题】15.汉明距离——Java版
  54. 【leetcode刷题】14.找到所有数组中消失的数字——Java版
  55. 【leetcode刷题】13.比特位计数——Java版
  56. oracle控制用户权限命令
  57. 三年Java开发,继阿里,鲁班二期Java架构师
  58. Oracle必须要启动的服务
  59. 万字长文!深入剖析HashMap,Java基础笔试题大全带答案
  60. 一问Kafka就心慌?我却凭着这份,图灵学院vip课程百度云