[英]Map of maps - how to keep the inner maps as maps?
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. 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。
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. 但是,当我得到每个内部地图时,我创建的地图最初变成了一个对象,我不能像使用外部地图那样使用键来访问它的值。
To learn from you experts, I would like to know how to keep all the maps as maps. 要向您学习专家,我想知道如何将所有地图保留为地图。 Or, is it possible at all?
或者,它有可能吗?
here is my exercise program: 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));
}
}
}
SOLUTIONS: 解决方案:
Map<Object,Map<Object,String>
Map<String, Object> mpMaps=new HashMap<String, Object>();
by ameer and sleske 由ameer和sleske
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>
. 以下是似乎有效的更新代码,您需要将地图的地图键入为
<String, Object>
因为mp不是您不能执行的字符串<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>();
// 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));
}
}
}
Your code does not compile. 您的代码无法编译。
One problem is this: 一个问题是:
Map<Object,String> mpMaps=new HashMap();
mpMaps.put("Map1",mp);
This won't work, as you put a Map ( mp
) into a Map whose values need to be Strings
. 这不起作用,因为您将Map(
mp
)放入其值必须为Strings
的Map中。
Use Map<Object,Map<Object,String>
and you should be fine. 使用
Map<Object,Map<Object,String>
,你应该没问题。
An alternate solution would be to use Commons MultiKey for avoiding map of maps. 另一种解决方案是使用Commons MultiKey来避免地图的映射。 See details at http://commons.apache.org/collections/apidocs/ and org.apache.commons.collections.keyvalue.MultiKey
请参阅http://commons.apache.org/collections/apidocs/和org.apache.commons.collections.keyvalue.MultiKey上的详细信息
Map<Object,String> mpMaps=new HashMap();
mpMaps.put("Map1",mp);
you'll get an exception with this statement: mp has type Map but you're treating it as a String. 你会得到这个语句的异常:mp有类型Map但你把它当作一个String。
If I understood your question right, you'll either need a reference to the object used as key or you'll need to type cast your key/values. 如果我理解你的问题,你需要引用用作键的对象,或者你需要键入转换你的键/值。
Here is a simple example using HashMap
这是一个使用
HashMap
的简单示例
HashMap<String, HashMap<String, Object>> outerMap = new HashMap<String, HashMap<String, Object>>();
HashMap<String, Object> innerMap1 = new HashMap<String, Object>();
HashMap<String, Object> innerMap2 = new HashMap<String, Object>();
innerMap1.put("Name", "az");
innerMap1.put("Address", "7 lab");
innerMap1.put("Age", 40);
innerMap2.put("Name", "sab");
innerMap2.put("Address", "bk3");
innerMap2.put("Age", 35);
outerMap.put("1",innerMap1);
outerMap.put("2", innerMap2);
System.out.println("outerMap = " + outerMap);
output: 输出:
outerMap = {1={Address=7 lab, Age=40, Name=az}, 2={Address=bk3, Age=35, Name=sab}}
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