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 1 package com.journaldev.util;
 2
 3 import java.util.HashMap;
 4 import java.util.Iterator;
 5 import java.util.Map;
 6 import java.util.concurrent.ConcurrentHashMap;
 7
 8 public class ConcurrentHashMapExample {
 9
10     public static void main(String[] args) {
11
12         //ConcurrentHashMap
13         Map<String,String> myMap = new ConcurrentHashMap<String,String>();
14         myMap.put("1", "1");
15         myMap.put("2", "1");
16         myMap.put("3", "1");
17         myMap.put("4", "1");
18         myMap.put("5", "1");
19         myMap.put("6", "1");
20         System.out.println("ConcurrentHashMap before iterator: "+myMap);
21         Iterator<String> it = myMap.keySet().iterator();
22
23         while(it.hasNext()){
24             String key = it.next();
25             if(key.equals("3")) myMap.put(key+"new", "new3");
26         }
27         System.out.println("ConcurrentHashMap after iterator: "+myMap);
28
29         //HashMap
30         myMap = new HashMap<String,String>();
31         myMap.put("1", "1");
32         myMap.put("2", "1");
33         myMap.put("3", "1");
34         myMap.put("4", "1");
35         myMap.put("5", "1");
36         myMap.put("6", "1");
37         System.out.println("HashMap before iterator: "+myMap);
38         Iterator<String> it1 = myMap.keySet().iterator();
39
40         while(it1.hasNext()){
41             String key = it1.next();
42             if(key.equals("3")) myMap.put(key+"new", "new3");
43         }
44         System.out.println("HashMap after iterator: "+myMap);
45     }
46
47 }

package com.journaldev.util;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

public class ConcurrentHashMapExample {

    public static void main(String[] args) {

        //ConcurrentHashMap
        Map<String,String> myMap = new ConcurrentHashMap<String,String>();
        myMap.put("1", "1");
        myMap.put("2", "1");
        myMap.put("3", "1");
        myMap.put("4", "1");
        myMap.put("5", "1");
        myMap.put("6", "1");
        System.out.println("ConcurrentHashMap before iterator: "+myMap);
        Iterator<String> it = myMap.keySet().iterator();

        while(it.hasNext()){
            String key = it.next();
            if(key.equals("3")) myMap.put(key+"new", "new3");
        }
        System.out.println("ConcurrentHashMap after iterator: "+myMap);

        //HashMap
        myMap = new HashMap<String,String>();
        myMap.put("1", "1");
        myMap.put("2", "1");
        myMap.put("3", "1");
        myMap.put("4", "1");
        myMap.put("5", "1");
        myMap.put("6", "1");
        System.out.println("HashMap before iterator: "+myMap);
        Iterator<String> it1 = myMap.keySet().iterator();

        while(it1.hasNext()){
            String key = it1.next();
            if(key.equals("3")) myMap.put(key+"new", "new3");
        }
        System.out.println("HashMap after iterator: "+myMap);
    }

}