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jdk1.8源码分析之HashMap

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原文链接：https://segmentfault.com/a/1190000012926722?utm_source=tag-newest 1.概述本篇文章我们来聊聊大家日常开发中常用的一个集合类 - HashMap 。HashMap 最早出现在 JDK 1.2中，底层基于散列算法实现。HashMap 允许 null 键和 null 值，在计算哈键的哈希值时，null 键哈希值为 0。HashMap 并不保证键值对的顺序，这意味着在进行某些操作后，键值对的顺序可能会发生变化。另外，需要注意的是，HashMap 是非线程安全类，在多线程环境下可能会存在问题。在本篇文章中，我将会对 HashMap 中常用方法、重要属性及相关方法进行分析。需要说明的是，HashMap 源码中可分析的点很多，本文很难一一覆盖，请见谅。 2.原理上一节说到 HashMap 底层是基于散列算法实现，散列算法分为散列再探测和拉链式。HashMap 则使用了拉链式的散列算法，并在 JDK 1.8 中引入了红黑树优化过长的链表。数据结构示意图如下：对于拉链式的散列算法，其数据结构是由数组和链表（或树形结构）组成。在进行增删查等操作时，首先要定位到元素的所在桶的位置，之后再从链表中定位该元素。比如我们要查询上图结构中是否包含元素 35 ，步骤如下：定位元素 35 所处桶的位置， index = 35 %

NSString hash collision doesn't mess up NSDictionary [closed]

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问题 Closed . This question needs details or clarity. It is not currently accepting answers. Want to improve this question? Add details and clarify the problem by editing this post. Closed 6 years ago . Run this code in the debugger and stop afterward (I'm in the iOS 7 simulator in Xcode 5.0.1). NSString *nsStr = @"/Users/123456789012/Library/Application Support/iPhone Simulator/7.0/Applications/94F31827-6DAD-4BD5-AC91-B215176265E1/Documents/libraries/shared/17517_abPub/OEBPS/indexes/Index.sqlite"

Sort hash by nested value

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问题 My hash looks like below. I want the output to be in the same hash form but with hash arranged according to the price. { 1=>{ "name"=>"Mark", "date"=>"27/08/2015", "bed"=>"3", "furnish"=>"Fully", "size"=>"10", "price"=>790000 }, 2=>{ "name"=>"Mark", "date"=>"27/08/2015", "bed"=>"3", "furnish"=>"Fully", "size"=>"10", "price"=>720000 }, 3=>{ "name"=>"Mark", "date"=>"27/08/2015", "bed"=>"3", "furnish"=>"Fully", "size"=>"10", "price"=>750000 }, 4=>{ "name"=>"Mark", "date"=>"27/08/2015", "bed"=>"3

Cost of Preimage attack

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问题 I need to know the cost of succeeding with a Preimage attack ("In cryptography, a preimage attack on a cryptographic hash is an attempt to find a message that has a specific hash value.", Wikipedia). The message I want to hash consists of six digits (the date of birth), then four random digits. This is a social security number. Is there also a possibility to hash something using a specific password. This would introduce another layer of security as one would have to know the password in order

How to retrieve the hash values in the views in rails

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问题 I have an action in the controller: def user_detail @user_detail = UserDetail.find_by_id(11) end And in the view: <%= @user_detail -%> // displays me like # I am trying to retrieve the contents of @user_detail: actually the hash contains {:empid=>"11111", :prjtname=>"aaaaa", :prjtrole=>"Developer"} How do I display the user detail's empid and other values? 回答1: Since I know what question you asked earlier, I think this is the syntax you actually want to use: <%= @user_detail.additional_info[

Login details security using salt n hash and a login role in postgresql

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问题 I am coding up the security for a website in express.js and postgresql db. Now I have been reading about salting and hashing and I have the code set up with pdkdf2 using the crypto module, but my issue is how I will structure the account table in the db. What If i would create a login role which will have an MD5 encrypted format for the password, which password will be the derived key from the salt n hash "procedure". Would that be an overkill of protection? There will be a table which will

Remove back slash in string

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问题 I am requesting user detail in facebook after getting token . I got the following response. Response as follows "{\"id\":\"xxxxx\",\"name\":\"abcd\",\"first_name\":\"ab\",\"last_name\":\"cd\", \"link\":\"http:\\/\\/www.facebook.com\\/profile.php?id=xxxxx\",\"quotes\":\"Life is a difficult game. You can win it only by retaining your birthright to be a person.\",\"gender\":\"female\",\"timezone\":5.5,\"locale\":\"en_US\",\"verified\":true,\"updated_time\":\"2012-02-22T12:59:39+0000\"}" I

clarifying facts behind Java's implementation of HashSet/HashMap

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问题 1. I understand the different hash map mechanisms and the ways in which key collisions are handled (either open addressing -linear/quadratic probing, chaining, extendable hashing, etc. Which one does HashSet/HashMap make use of? 2. I realise that a good HashMap relies on a good hash function. How does Java's HashSet/HashMap hash the objects? I know that there is a hash function but so far for strings I have not needed to implement this. What if I now want to Hash a Java Object that I create -

Pairwise independent hash functions in Java

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问题 I'm looking for a quick and easy way to use a (universal) family of pairwise independent hash functions in my Java projects. Ideally, I would have some object UniversalFamily (representing the Family) which would return me objects with a method hash() which hashes integers. Example usage: // use this object to generate pairwise independent hash functions UniversalFamily family = new UniversalFamily(); // these objects represent the pairwise independent hash functions HashF hashF1 = fam

Pairwise independent hash functions in Java

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