如何根據multimap中存在的值檢索密鑰？

Question

我有一些鍵指向多圖中的許多值。我如何檢索基於multimap中存在的值的鍵。這是我的代碼。

package com.manoj; 

import java.util.Set; 

import com.google.common.collect.ArrayListMultimap; 
import com.google.common.collect.Multimap; 

public class GuavaMap 
{ 
    public static void main(String[] args) 
    { 
     Multimap regions = ArrayListMultimap.create(); 
     regions.put("asia", "afganistan"); 
     regions.put("asia", "bangladesh"); 
     regions.put("asia", "inida"); 
     regions.put("asia", "japan"); 
     regions.put("asia", "burma"); 
     regions.put("europe", "andorra"); 
     regions.put("europe", "austria"); 
     regions.put("europe", "belgium"); 
     regions.put("europe", "cyprus"); 
     regions.put("oceania","australia"); 
     regions.put("oceania", "fiji"); 
     regions.put("oceania", "nauru"); 
     Set<String> keys = regions.keySet(); 
     System.out.println("key\t\t\t"+"values\t\t\t"); 
     System.out.println(); 
     String comp = null; 
     for(String key : keys) 
     { 
      System.out.print(key); 
      System.out.println(regions.get(key)); 
     } 
    } 
} 

上面的代碼如下

我提供的輸出，我需要的區域名稱基礎上的國家。

舉例：如果我給「澳大利亞」輸出應該是「大洋洲」

Answer 1

首先，我想建議不要使用原始類型和明確提到重點和值類型在創建地圖。

關於你的問題取決於價值的檢索關鍵字，您可以遍歷地圖的所有entries做同樣類似：

class GuavaMap 
{ 
    //Explicitly mentioned key and value both are Strings here 
    public static Multimap<String, String> regions = ArrayListMultimap.<String, String>create(); 
    public static void main(String[] args) 
    { 
     regions.put("asia", "afganistan"); 
     regions.put("asia", "bangladesh"); 
     regions.put("asia", "inida"); 
     regions.put("asia", "japan"); 
     regions.put("asia", "burma"); 
     regions.put("europe", "andorra"); 
     regions.put("europe", "austria"); 
     regions.put("europe", "belgium"); 
     regions.put("europe", "cyprus"); 
     regions.put("oceania","australia"); 
     regions.put("oceania", "fiji"); 
     regions.put("oceania", "nauru"); 
     Set<String> keys = regions.keySet(); 
     System.out.println("key\t\t\t"+"values\t\t\t"); 
     System.out.println(); 
     String comp = null; 
     for(String key : keys) 
     { 
      System.out.print(key); 
      System.out.println(regions.get(key)); 
     } 

     //usage of below defined method 
     String region = getRegion("australia"); 
     System.out.println("Region for australia:" + region); 
    } 

    // Function to get the region name i.e. key 
    public static String getRegion(String country){ 
     for(Entry<String, String> entry : regions.entries()){ 
      if(entry.getValue().equals(country)) 
       return entry.getKey(); 
     } 
     return "Not found"; 
    } 
} 

Answer 2

你可以反其道而行

Multimap<String, String> invregions = Multimaps.invertFrom(regions , ArrayListMultimap.<String, String>create()); 

，並調用get （「你的國家」）;

這會給你包含你的國家的鑰匙

Answer 3

感謝您的回覆。

我發現基於該列表，地圖和HashMap

package com.manoj; 

import java.util.ArrayList; 
import java.util.Arrays; 
import java.util.HashMap; 
import java.util.Iterator; 
import java.util.List; 
import java.util.Map; 
import java.util.Map.Entry; 
import java.util.Scanner; 

public class NestedList 
{ 
    public static void main(String[] args) 
    { 
     List asia = Arrays.asList("afganistan","japan","india","pakistan","singapore","sri lanka"); 
     List europe = Arrays.asList("albania","belarus","iceland","russia","norway","turkey"); 
     List middleEast = Arrays.asList("australia","new zealand","samoa","tonga","vanuatu"); 

     Map region = new HashMap<>(); 
     region.put("asia",asia); 
     region.put("europe", europe); 
     region.put("middleeast" ,middleEast); 
     String reg = null; 
     String val = null; 
     for(Object key : region.keySet()) 
     { 
      reg = key.toString(); 
      Iterator it = ((List) region.get(key)).iterator(); 
      while(it.hasNext()) 
      { 
       val = it.next().toString(); 
       if(val.equalsIgnoreCase("india"))//here you have to provide the country name 
       { 
        System.out.println(reg); 
       } 
      } 
     } 
    } 
}