Java HashMap关联多维数组无法创建或添加元素 [英] Java HashMap associative multi dimensional array can not create or add elements

问题描述

好的，所以我花了几个小时试图围绕 Java 中的 HashMap 这个概念进行思考，但我就是无法弄清楚.我看过很多教程，但似乎没有一个能满足我的确切要求，我无法让它工作.

Okay so I have spent several hours trying to wrap my head around this concept of a HashMap in Java but am just not able to figure it out. I have looked at many tutorials but none seem to address my exact requirement and I cannot get it to work.

我正在尝试在 Java(或类似的东西)中创建一个关联多维数组，以便我可以使用字符串键在数组中保存和检索.

I am trying to create an associative multi dimensional array in Java (or something similar) so that I can both save to and retrieve from the array with keys that are Strings.

这就是我在 PHP 中的做法，并最好地解释了我正在尝试做的事情:

This is how I would do it in PHP and explains it best what I am trying to do:

//loop one - assign the names
myArray['en']['name'] = "english name";
myArray['fr']['name'] = "french name";
myArray['es']['name'] = "spanish name";

//loop two - assign the description
myArray['en']['desc'] = "english description";
myArray['fr']['desc'] = "french description";
myArray['es']['desc'] = "spanish description";

//loop three - assign the keywords
myArray['en']['keys'] = "english keywords";
myArray['fr']['keys'] = "french keywords";
myArray['es']['keys'] = "spanish keywords";

//later on in the code be able to retrive any value similar to this
english_name = myArray['en']['name'];
french_name = myArray['fr']['name'];
spanish_name = myArray['es']['name'];

这是我在 Java 中尝试过的，但它不起作用:

This is what I tried in Java but it is not working:

HashMap<String, HashMap<String, String>> myArray = new HashMap<String, HashMap<String, String>>();

myArray.put("en" , put("name", "english name")); //gives me "cannot find symbol" at second put

myArray.put("en" , ("name", "english name")); //gives me "')' expected" after second comma

所以我确定我缺少一些简单的东西，但请指出，因为这非常令人沮丧！

So I am sure its something simple that I am missing but please point it out because this is very frustrating!

谢谢

所以这里有一些关于我如何实现我接受的答案的工作代码:

So here is some working code on how I implemented the answer I accepted:

import java.util.*;

HashMap<String, HashMap<String, String>> finalArray = new HashMap<String, HashMap<String, String>>();

String[] langArray = {"en","fr","de","no","es"};

//Initialize each language key ahead of time
for(String lang : langArray) { // foreach lang in langArray
  if (!finalArray.containsKey(lang)) {
    finalArray.put(lang, new HashMap<String, String>());
  }
}

//loop one - assign names
for(String lang : langArray) {
  String theName = lang + " name"; //go get the name from somewhere
  finalArray.get(lang).put("name", theName);
}

//loop two - assign description
for(String lang : langArray) {
  String theDesc = lang + " description"; //go get the description from somewhere
  finalArray.get(lang).put("desc", theDesc);
}

//loop three - assign keywords
for(String lang : langArray) {
  String theKeys = lang + " keywords"; //go get the keywords from somewhere
  finalArray.get(lang).put("keys", theKeys);
}

//display output
for(String lang : langArray) {
  System.out.println("LANGUAGE: " + lang);
  System.out.println(finalArray.get(lang).get("name"));
  System.out.println(finalArray.get(lang).get("desc"));
  System.out.println(finalArray.get(lang).get("keys"));
}

//example to retrieve/get values
String english_name = finalArray.get("en").get("name");
String french_desc = finalArray.get("fr").get("desc");

推荐答案

HashMap<String, HashMap<String, String>> myArray = new HashMap<String, HashMap<String, String>>();

if (!myArray.containsKey("en")) {
    myArray.put("en", new HashMap<String, String>());
}
myArray.get("en").put("name", "english name");

在 Java 中，您必须明确说明何时创建对象.在这种情况下，首先我们检查是否已经有一个 HashMap 对象存储在我们的外部 HashMap 中的键en"下.如果没有，我们创建一个空的.

In Java you have to be explicit about when you are creating an object. In this case first we check if there is already a HashMap object stored in our outer HashMap under the key "en". If not, we create an empty one.

现在要放入一个新值，我们必须首先从外部 HashMap 中获取它，然后放入新值.

Now to put a new value into it we have to first get it from the outer HashMap, then put the new value.

这篇关于Java HashMap关联多维数组无法创建或添加元素的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！