hashmap

Java对Map排序

由 拥有回忆 提交于 2020-01-05 04:39:56
Java中对Map(HashMap,TreeMap,Hashtable等)的排序时间 首先简单说一下他们之间的区别： HashMap: 最常用的Map,它根据键的HashCode 值存储数据,根据键可以直接获取它的值，具有很快的访问速度。HashMap最多只允许一条记录的键为Null(多条会覆盖);允许多条记录的值为 Null。非 首先简单说一下他们之间的区别： HashMap: 最常用的Map,它根据键的HashCode 值存储数据,根据键可以直接获取它的值，具有很快的访问速度。HashMap最多只允许一条记录的键为Null(多条会覆盖);允许多条记录的值为 Null。非同步的。 TreeMap: 能够把它保存的记录根据键(key)排序,默认是按升序排序，也可以指定排序的比较器，当用Iterator 遍历TreeMap时，得到的记录是排过序的。TreeMap不允许key的值为null。非同步的。 Hashtable: 与 HashMap类似,不同的是:key和value的值均不允许为null;它支持线程的同步，即任一时刻只有一个线程能写Hashtable,因此也导致了Hashtale在写入时会比较慢。 LinkedHashMap: 保存了记录的插入顺序，在用Iterator遍历LinkedHashMap时，先得到的记录肯定是先插入的.在遍历的时候会比HashMap慢

java dynamic attributes table

由 帅比萌擦擦* 提交于 2020-01-05 04:16:15
问题 I am developing a java application which needs a special component for dynamic attributes. The arguments are serialized (using JSON) and stored in a database and then deserialized at runtime. All attributes are displayed in a JTable with 3 columns (attribute name, attribute type and attribute value) and stored in a hashmap. I have currently two problems to solve: The hashmap can also store objects and the objects can be set to null. And if set to null i dont know which class they belong to.

Fine tuning hash to dynamically create ZingCharts treemap array

由 末鹿安然 提交于 2020-01-05 04:04:20
问题 First : Thanks for reading, but there is a lot in this, it may be easier to see it in the CodePen examples that are linked at the bottom. I recently asked a question about how to dynamically create an array for a treemap, and was pointed in the right direction. I have been able to do some simple manipulation to the hash table, but can't figure out how to do the final step. Currently the treemap has 2 "levels", that was done like this: var data=[{color:"blue",party:"Democratic",text:

JSTL Access Integer/Long key in Hash Map

由 橙三吉。 提交于 2020-01-05 03:18:20
问题 I am facing some problem in using EL in JSTL and not able to access Java Hash Map as I would like. I am aware that in EL the key, if Integer gets accessed as Long. I have following hash map definition that I am trying to access in JSTL - Map<Long, Object> testMap = new HashMap<Long, Object>(); In JSP page, I need to check if the map contains a specific key or not. I attempt to do that by checking if not empty as following - <c:if test='${ ! empty testMap[currObj.currVal]}'> I also access the

Confusion about Rust HashMap and String borrowing

由 女生的网名这么多〃 提交于 2020-01-05 03:04:52
问题 This program accepts an integer N, followed by N lines containing two strings separated by a space. I want to put those lines into a HashMap using the first string as the key and the second string as the value: use std::collections::HashMap; use std::io; fn main() { let mut input = String::new(); io::stdin().read_line(&mut input) .expect("unable to read line"); let desc_num: u32 = match input.trim().parse() { Ok(num) => num, Err(_) => panic!("unable to parse") }; let mut map = HashMap::<&str,

Confusion about Rust HashMap and String borrowing

由 好久不见. 提交于 2020-01-05 03:04:42
问题 This program accepts an integer N, followed by N lines containing two strings separated by a space. I want to put those lines into a HashMap using the first string as the key and the second string as the value: use std::collections::HashMap; use std::io; fn main() { let mut input = String::new(); io::stdin().read_line(&mut input) .expect("unable to read line"); let desc_num: u32 = match input.trim().parse() { Ok(num) => num, Err(_) => panic!("unable to parse") }; let mut map = HashMap::<&str,

Issue with Hash Map Space

由 天涯浪子 提交于 2020-01-05 03:04:20
问题 In my Java code, I am using Guava's Multimap (com.google.common.collect.Multimap) by using this: Multimap<Integer, Integer> Index = HashMultimap.create() Here, Multimap key is some portion of a URL and value is another portion of the URL (converted into an integer). Now, I assign my JVM 2560 Mb (2.5 GB) heap space (by using Xmx and Xms). However, it can only store 9 millions of such (key,value) pairs of integers (approx 10 million). Now, issue is, I can provide JVM only limited amount of

Issue with Hash Map Space

由 一曲冷凌霜 提交于 2020-01-05 03:03:17
问题 In my Java code, I am using Guava's Multimap (com.google.common.collect.Multimap) by using this: Multimap<Integer, Integer> Index = HashMultimap.create() Here, Multimap key is some portion of a URL and value is another portion of the URL (converted into an integer). Now, I assign my JVM 2560 Mb (2.5 GB) heap space (by using Xmx and Xms). However, it can only store 9 millions of such (key,value) pairs of integers (approx 10 million). Now, issue is, I can provide JVM only limited amount of

Which value for a duplicate key is ignored in a Ruby hash?

由 ♀尐吖头ヾ 提交于 2020-01-05 02:52:08
问题 If a hash has more than one occurrences of identical keys pointing to different values, then how does Ruby determine which value is assigned to that key? In other words, hash = {keyone: 'value1', keytwo: 'value2', keyone: 'value3'} results in warning: duplicated key at line 1 ignored: :keyone but how do I know which value is assigned to :keyone ? 回答1: The last one overwrites the previous values. In this case, "value3" becomes the value for :keyone . This works just as the same with merge .

[转]Java中常用的集合—初学者的你不可错过的精编整理

由 旧街凉风 提交于 2020-01-05 02:29:32
集合一直都是项目中非常常见的，我是一个Android开发者，集合对于我来说，在项目中使用的次数非常之多，因为使用的多，熟能生巧，所以这里呢！就给那些初学者整理一下Java当中常用的集合吧！   因为此篇文章是给初学者看到，所以对于集合的认识，我们就不从内存的角度去分析了，等你Java学到一定的时候，再去学习一下集合的底层实现，这会让成为一名更加牛的Java程序员。   在整理之前呢，我们先聊一聊为什么集合会这么常用？，集合这个概念，我们初次接触是在高中的数学当中，高中的集合具有以下知识点： 　　1、集合的含义：某些指定的对象集在一起就成为一个集合，其中每一个对象叫元素。 　　2、集合的中元素的三个特性： 　　①.元素的确定性；②.元素的互异性；③.元素的无序性 　　说明： (1)对于一个给定的集合，集合中的元素是确定的，任何一个对象或者是或者不是这个给定的集合的元素。 　　(2)任何一个给定的集合中，任何两个元素都是不同的对象，相同的对象归入一个集合时，仅算一个元素。 　　(3)集合中的元素是平等的，没有先后顺序，因此判定两个集合是否一样，仅需比较它们的元素是否一样，不需考查排列顺序是否一样。   高中的集合理解起来很简单，高中的集合里面放到是一个一个具体的对象，集合当中对象与对象之间是不一样的，而且集合中对象的元素是杂乱无章的，顺序没有什么规律可循，因为高中集合是无序性的
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