Java Collection - 如何将HashMap转换为Hashtable

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

public class Main {
  public static void main(String[] args) {

    HashMap<String, String> hMap = new HashMap<String, String>();

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

    Hashtable<String, String> ht = new Hashtable<String, String>();
    ht.put("1", "REPLACED !!");
    ht.put("4", "Four");

    Enumeration e = ht.elements();
    while (e.hasMoreElements()){
      System.out.println(e.nextElement());
    }      

    ht.putAll(hMap);
    e = ht.elements();

    while (e.hasMoreElements()){
      System.out.println(e.nextElement());
    }      
  }
}