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About Byron Kiourtzoglou

Byron Kiourtzoglou
Byron is a master software engineer working in the IT and Telecom domains. He is an applications developer in a wide variety of applications/services. He is currently acting as the team leader and technical architect for a proprietary service creation and integration platform for both the IT and Telecom industries in addition to a in-house big data real-time analytics solution. He is always fascinated by SOA, middleware services and mobile development. Byron is co-founder and Executive Editor at Java Code Geeks.

Copy all elements of Hashmap to Hashtable example

This is an example of how to copy all elements of a HashMap to a Hashtable. Coping HashMap elements to a Hashtable implies that you should:

  • Create a new HashMap.
  • Populate the hashmap with elements, using put(K key, V value) API method of HashMap.
  • Create a new Hashtable.
  • Populate the hashtable with elements, using put(K key, V value) API method of Hashtable.
  • Invoke putAll(Map m) API method of Hashtable, with the hashMap created above as parameter. The method copies all of the mappings from the specified map to the hashtable. These mappings will replace any mappings that this hashtable had for any of the keys currently in the specified map.

Let’s take a look at the code snippet that follows:

package com.javacodegeeks.snippets.core;
 
import java.util.Hashtable;
import java.util.HashMap;
 
public class CopyHashMapToHashtable {
 
  public static void main(String[] args) {
 
    // Create a HashMap and populate it with elements
    HashMap hashmap = new HashMap();
    hashmap.put("key_1","new_value_1");
    hashmap.put("key_2","value_2");
 
    // Create a Hashtable and populate it with elements
    Hashtable hashtable = new Hashtable();
    hashtable.put("key_1","value_1");
    hashtable.put("key_3","value_3");
    hashtable.put("key_4","value_4");
 
    System.out.println("Elements in Hashtable : " + hashtable);
 
    // void putAll(Map m) copies Map entries to Hashtable replacing existing mapping of keys
    hashtable.putAll(hashmap);
 
    System.out.println("Elements in Hashtable : " + hashtable);
 
  }
} 

Output:

Elements in Hashtable : {key_4=value_4, key_3=value_3, key_1=value_1}
Elements in Hashtable : {key_4=value_4, key_3=value_3, key_2=value_2, key_1=new_value_1}

 
This was an example of how to copy all elements of a HashMap to a Hashtable in Java.

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