hashmap | 易学教程

Can internal dictionary order change?

阅读更多关于 Can internal dictionary order change?

问题 exampleDict = {'a':1, 'b':2, 'c':3, 'd':4} The above dictionary initially iterated through in this order: b=2 d=4 a=1 c=3 Then, I moved around a ton of files in my code, and now it iterates through in this order: d=4 a=1 c=3 b=2 I know that the order is internally stored as a hashmap, but what would cause that internal order to change? Edit: I don't need to preserve order so I will stick with using a dict. I am just wondering why it happened. I thought order wasn't guaranteed, but once it has

几种简单的负载均衡算法及其Java代码实现

阅读更多关于几种简单的负载均衡算法及其Java代码实现

什么是负载均衡负载均衡，英文名称为Load Balance，指由多台服务器以对称的方式组成一个服务器集合，每台服务器都具有等价的地位，都可以单独对外提供服务而无须其他服务器的辅助。通过某种负载分担技术，将外部发送来的请求均匀分配到对称结构中的某一台服务器上，而接收到请求的服务器独立地回应客户的请求。负载均衡能够平均分配客户请求到服务器阵列，借此提供快速获取重要数据，解决大量并发访问服务问题，这种集群技术可以用最少的投资获得接近于大型主机的性能。负载均衡分为软件负载均衡和硬件负载均衡，前者的代表是阿里章文嵩博士研发的LVS，后者则是均衡服务器比如F5，当然这只是提一下，不是重点。本文讲述的是" 将外部发送来的请求均匀分配到对称结构中的某一台服务器上 "的各种算法，并以Java代码演示每种算法的具体实现，OK，下面进入正题，在进入正题前，先写一个类来模拟Ip列表： 1 public class IpMap 2 { 3 // 待路由的Ip列表，Key代表Ip，Value代表该Ip的权重 4 public static HashMap<String, Integer> serverWeightMap = 5 new HashMap<String, Integer>(); 6 7 static 8 { 9 serverWeightMap.put("192.168.1.100",

HashMap: iterating the key-value pairs in random order

阅读更多关于 HashMap: iterating the key-value pairs in random order

问题 I have a HashMap and I'd like to iterate they key-value pairs in a different random order each time i get the iterator. Conceptually I'd like to "shuffle" the map before calling the iterator (or if you want, "shuffle" the iterator). I have two options i see: 1) use the approach of LinkedHashMap and keep a list of the entries internally, shuffle it in-place and return that view when the iterator is called. 2) take map.entrySet(), construct an ArrayList and use shuffle() on it. While the two

How do I take a compressed file (through indexes) and re-create the original file? (Java)

阅读更多关于 How do I take a compressed file (through indexes) and re-create the original file? (Java)

问题 Background of question I have been developing some code that focuses on firstly, reading a string and creating a file. Secondly, spliting a string into an array. Then getting the indexes for each word in the array and finally, removing the duplicates and printing it to a different file. I currently have made the code for this here is a link https://pastebin.com/gqWH0x0 (there is a menu system as well) but it is rather long so I have refrained from implementing it in this question. The

Getting data from JSON

阅读更多关于 Getting data from JSON

问题 I'm trying to get the values out of this JSON string but I'm having a hard time achieving this. {"DebugLogId":"1750550","RequestId":"17505503","Result": {"Code":"","DebugLogId":"1750550","Message":""}, "Suggestions":[ {"Ranking":"1","Score":"60","Title":"This is a test message 1"}, {"Ranking":"2","Score":"60","Title":"This is a test message 2"} ]} What way would be easiest to access the data in 'Suggestions'? I'm using the GSON module. Ideally I would like to put it all in a HashMap. Thanks

Getting data from JSON

阅读更多关于 Getting data from JSON

Create a HashMap with a fixed Key corresponding to a HashSet. point of departure

阅读更多关于 Create a HashMap with a fixed Key corresponding to a HashSet. point of departure

问题 My aim is to create a hashmap with a String as the key, and the entry values as a HashSet of Strings. OUTPUT This is what the output looks like now: Hudson+(surname)=[Q2720681], Hudson,+Quebec=[Q141445], Hudson+(given+name)=[Q5928530], Hudson,+Colorado=[Q2272323], Hudson,+Illinois=[Q2672022], Hudson,+Indiana=[Q2710584], Hudson,+Ontario=[Q5928505], Hudson,+Buenos+Aires+Province=[Q10298710], Hudson,+Florida=[Q768903]] According to my idea, it should look like this: [Hudson+(surname)=[Q2720681

How would I print values from a HashMap while not printing duplicates?

阅读更多关于 How would I print values from a HashMap while not printing duplicates?

问题 I'm trying to fix this piece of code where I'm printing from a hashmap having a list of plate numbers and owners (that format). I'm trying to print out just the owners via printOwners(); but I can't get it to not print duplicates. I've played around with it for a while, just can't seem to skip over duplicates. Here is my code: import java.util.ArrayList; import java.util.HashMap; public class VehicleRegister { private HashMap<RegistrationPlate, String> owners; public VehicleRegister() {

Why does count++ (instead of count = count + 1) change the way the map is returned in Golang

阅读更多关于 Why does count++ (instead of count = count + 1) change the way the map is returned in Golang

问题 I used a map that uses words from a sentence as its keys and integers as the values. func WordCount(s string) map[string]int { var m map[string]int m = make(map[string]int) var substrings[]string count := 0 substrings = strings.Split(s, " ") for i := range substrings { count = count + 1 m[substrings[i]] = count } return m } func main() { fmt.Println(WordCount("I am learning GO since some days")) } The above code ALWAYS displays the map in the correct order, i.e. map[I:1 am:2 learning:3 GO:4

Why does this code sometimes throw a NullPointerException?

阅读更多关于 Why does this code sometimes throw a NullPointerException?

问题 Consider the following Java source: if( agents != null ) { for( Iterator iter = agents.keySet().iterator(); iter.hasNext(); ) { // Code that uses iter.next() ... // } } The agents is a HashMap . Why does the for statement sometimes throw a NullPointerException ? Thank you. 回答1: Thread Safety If your code is multi-threaded, then it is possible. For example: public class C { private Hashtable agents = new Hashtable(); public iterate() { if( agents != null ) { for (Iterator iter = agents.keySet(