地图地图 - 如何将内部地图保存为地图？ [英] Map of maps - how to keep the inner maps as maps?

问题描述

我的目标是创建地图的地图，以便我可以通过其关键字检索外部地图的信息，然后通过它们的键访问其内部地图。然而，当我获得每个内部地图时，我创建的地图最初成为一个对象，并且我不能像使用外部地图一样使用键来访问它的值。 / p>

为了向您学习专家，我想知道如何将所有地图保存为地图。或者，有没有可能？

这是我的锻炼计划：

  import java.util.HashMap; 
 import java.util.Iterator; 
 import java.util.Map; 
 import java.util.Set; 
 
 public class MapExample {
 
 public static void main（String [] args）{
 
 Map< Object，String> mp = new HashMap< Object，String>（）; 
 
 //通过put方法键和值对在Map中添加或设置元素
 mp.put（new Integer（2），Two）; 
 mp.put（new Integer（1），One）; 
 mp.put（new Integer（3），Three）; 
 mp.put（新整数（4），四）; 
 
地图< Object，String> mp2 = new HashMap< Object，String>（）; 
 mp2.put（new Integer（2），Two2）; 
 mp2.put（new Integer（1），One2）; 
 mp2.put（new Integer（3），Three2）; 
 mp2.put（新的整数（4），Four2）; 
 
地图< Object，String> mpMaps = new HashMap（）; 
 
 mpMaps.put（Map1，mp）; 
 mpMaps.put（Map2，mp2）; 
 
 System.out.println（这是地图的地图：+ mpMaps）; 
 
 for（int i = 0; i< mpMaps.size（）; i ++）{
 ArrayList a = new ArrayList（mpMaps.keySet（））; 
 Object o = a.get（i）; 
 System.out.println（all together：+ mpMaps.size（）+each element is：+ o +value：+ mpMaps.get（o））; 
} 
} 
} 
  

解决方案：

 映射< Object，Map< Object，String> 
地图< String，Object> mpMaps = new HashMap< String，Object>（）; 
  

by ameer and sleske

解决方案

以下是更新后的代码，您需要将地图映射为< String，Object> ，因为mp isn'你不能做的字符串< Object，String> 。

  import java.util.HashMap; 
 import java.util.Iterator; 
 import java.util.Map; 
 import java.util.Set; 
 import java.util.ArrayList; 
 
 public class MapExample {
 
 public static void main（String [] args）{
 
 Map< Object，String> mp = new HashMap< Object，String>（）; 
 
 //通过put方法键和值对在Map中添加或设置元素
 mp.put（new Integer（2），Two）; 
 mp.put（new Integer（1），One）; 
 mp.put（new Integer（3），Three）; 
 mp.put（新整数（4），四）; 
 
地图< Object，String> mp2 = new HashMap< Object，String>（）; 
 mp2.put（new Integer（2），Two2）; 
 mp2.put（new Integer（1），One2）; 
 mp2.put（new Integer（3），Three2）; 
 mp2.put（新的整数（4），Four2）; 
 
地图< String，Object> mpMaps = new HashMap< String，Object>（）; 
 
 mpMaps.put（Map1，mp）; 
 mpMaps.put（Map2，mp2）; 
 
 System.out.println（这是地图的地图：+ mpMaps）; 
 
 for（int i = 0; i< mpMaps.size（）; i ++）{
 ArrayList< Object> a = new ArrayList< Object>（mpMaps.keySet（））; 
 Object o = a.get（i）; 
 System.out.println（all together：+ mpMaps.size（）+each element is：+ o +value：+ mpMaps.get（o））; 
} 
} 
} 
  

My goal is to create a map of maps so that I can retrieve info of the outer map by its key and then access its "inner" maps by their keys.

However, when I got each inner map, the map I created originally became an Object and I cannot use key to access its value as I do with the outer map.

To learn from you experts, I would like to know how to keep all the maps as maps. Or, is it possible at all?

here is my exercise program:

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

public class MapExample {

    public static void main(String[] args) {

        Map<Object,String> mp=new HashMap<Object, String>();

        // adding or set elements in Map by put method key and value pair
        mp.put(new Integer(2), "Two");
        mp.put(new Integer(1), "One");
        mp.put(new Integer(3), "Three");
        mp.put(new Integer(4), "Four");

        Map<Object,String> mp2=new HashMap<Object, String>();
        mp2.put(new Integer(2), "Two2");
        mp2.put(new Integer(1), "One2");
        mp2.put(new Integer(3), "Three2");
        mp2.put(new Integer(4), "Four2");

        Map<Object,String> mpMaps=new HashMap();

        mpMaps.put("Map1",mp);
        mpMaps.put("Map2",mp2);

        System.out.println("This is a map of Maps:   " + mpMaps); 

        for (int i=0;i<mpMaps.size();i++){
                     ArrayList a = new ArrayList(mpMaps.keySet());
                     Object o=a.get(i);
                     System.out.println("all together: " + mpMaps.size() + "each element is:  " + o + " value: " + mpMaps.get(o));
        }             
    }
}

SOLUTIONS:

   Map<Object,Map<Object,String>
    Map<String, Object> mpMaps=new HashMap<String, Object>(); 

by ameer and sleske

解决方案

Here is the updated code that seems to work, you need to type the map of maps as <String, Object> since mp isn't a string you can't do <Object, String>.

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.ArrayList;

public class MapExample {

    public static void main(String[] args) {

        Map<Object,String> mp=new HashMap<Object, String>();

        // adding or set elements in Map by put method key and value pair
        mp.put(new Integer(2), "Two");
        mp.put(new Integer(1), "One");
        mp.put(new Integer(3), "Three");
        mp.put(new Integer(4), "Four");

        Map<Object,String> mp2=new HashMap<Object, String>();
        mp2.put(new Integer(2), "Two2");
        mp2.put(new Integer(1), "One2");
        mp2.put(new Integer(3), "Three2");
        mp2.put(new Integer(4), "Four2");

        Map<String, Object> mpMaps=new HashMap<String, Object>();

        mpMaps.put("Map1",mp);
        mpMaps.put("Map2",mp2);

        System.out.println("This is a map of Maps:   " + mpMaps); 

        for (int i=0;i<mpMaps.size();i++){
                     ArrayList<Object> a = new ArrayList<Object>(mpMaps.keySet());
                     Object o=a.get(i);
                     System.out.println("all together: " + mpMaps.size() + "each element is:  " + o + " value: " + mpMaps.get(o));
        }             
    }
}

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