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I want to Create Java Hashtable from HashMap.

 HashMap hMap = new HashMap();       
//populate HashMap
hMap.put("1","One");
hMap.put("2","Two");
hMap.put("3","Three");

//create new Hashtable
Hashtable ht = new Hashtable();

//populate Hashtable
ht.put("1","This value would be REPLACED !!");
ht.put("4","Four");

After this what will be the easiest procedure?

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    `Hashtable ht = new Hashtable(hMap);` or `ht.putAll(hMap);`. Use the [API documentation](http://docs.oracle.com/javase/8/docs/api/java/util/Hashtable.html). Also, you should use generics and not use [raw types](https://stackoverflow.com/questions/2770321/what-is-a-raw-type-and-why-shouldnt-we-use-it). – Jesper Sep 08 '17 at 10:21
  • Yes but I am bound to follow the requirement. @AndyTurner thanks friend –  Sep 08 '17 at 10:24
  • OK @Jesper got it thanks friend –  Sep 08 '17 at 10:24
  • Why do you want to use a `Hashtable`? – Kayaman Sep 08 '17 at 10:36
  • hashtable ,raw types? can you explain what exactly are you trying to achieve? – Eugene Sep 08 '17 at 11:44

2 Answers2

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Use the Hashtable constructor that accepts a Map : 

public Hashtable(Map<? extends K, ? extends V> t)

And also you should favor generic types on raw types and program by interface as you declare your Map instances:

Map<String,String> hMap = new HashMap<>();       
//populate HashMap
hMap.put("1","One");
hMap.put("2","Two");
hMap.put("3","Three");

//create new Hashtable
Map<String,String> ht = new Hashtable<>(hMap);
davidxxx
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  • @Minati Das: `Enumeration` is as outdated as `Hashtable `, but if you really need it, use the [`Collections.enumeration` bridge](https://docs.oracle.com/javase/8/docs/api/java/util/Collections.html#enumeration-java.util.Collection-), e.g. instead of `hashtable.keys()`, you can use `Collections .enumeration(map.keySet())` and instead of `hashtable.elements()`, you can use `Collections.enumeration(map.values())`. But normally you use an `Iterator` or just a for-each loop, `for(String key: map.keySet()) …` or `for(String value: map.values()) …` – Holger Sep 08 '17 at 11:47
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Whoomp!! I have done successfully.. here it is :)

import java.util.Enumeration;
import java.util.Hashtable;
import java.util.HashMap;

public class CreateHashtableFromHashMap {

  public static void main(String[] args) {

    //create HashMap
    HashMap hMap = new HashMap();

    //populate HashMap
    hMap.put("1","One");
    hMap.put("2","Two");
    hMap.put("3","Three");

    //create new Hashtable
    Hashtable ht = new Hashtable();

    //populate Hashtable
    ht.put("1","This value would be REPLACED !!");
    ht.put("4","Four");

    //print values of Hashtable before copy from HashMap
    System.out.println("hastable contents displaying before copy");
    Enumeration e = ht.elements();
    while(e.hasMoreElements())
    System.out.println(e.nextElement());

    ht.putAll(hMap);

    //Display contents of Hashtable
    System.out.println("hashtable contents displaying after copy");
    e = ht.elements();
    while(e.hasMoreElements())
    System.out.println(e.nextElement());

  }
}