问题描述

我的目标是创建一个地图地图，以便我可以通过其键检索外部地图的信息，然后通过其键访问其内部"地图.

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.

但是，当我得到每个内部地图时，我最初创建的地图变成了一个对象，我不能像使用外部地图那样使用键来访问它的值.

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.

为了向各位专家学习，我想知道如何将所有地图保留为地图.或者，有可能吗?

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

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>();

        // 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));
        }             
    }
}

解决方案:

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

阿米尔和斯莱斯克

推荐答案

这是更新后的代码，似乎可以工作，您需要将地图的地图键入为 <String, Object> 因为mp 不是你不能做的字符串 <Object, String>.

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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