Code to Add duplicate key in Map

In Java Collections, Map Object won't accept duplicate key. There are some instances where we may need to have the Map functionality with duplicate key. This code helps to add duplicate key in a Map

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

public class DuplicateKey {

 static Map<String, ArrayList<String>> hashMap = new HashMap<String,  ArrayList<String>>();
 
 public static void main(String[] args) {
  retrieveValues();
 } 
 public static void retrieveValues()
 {   
  addValues("A", "a1");
  addValues("A", "a2");
  addValues("B", "b1");
  addValues("B", "b2");
  addValues("C", "c1");   
  
  Iterator<String> it = hashMap.keySet().iterator(); 
  ArrayList<String> tempList = null;

       while(it.hasNext()){ 
           String key = it.next().toString();
             tempList = hashMap.get(key);
            if(tempList != null){
                for(String value: tempList){ 
                   System.out.println("Key : "+key+ " ,  Value : "+value); }
               } 
        }
 }  
 //Method to add duplicate key and values
 private static void addValues(String key, String value)
 { 
  ArrayList<String> tempList = null;      
  if(hashMap.containsKey(key)){  
   tempList=hashMap.get(key); 
   if(tempList == null)    
     tempList = new ArrayList<String>();     
   tempList.add(value);    
  }
  else
  {     
   tempList = new ArrayList();  
   tempList.add(value);     
   }     
  hashMap.put(key,tempList);
 } 
}