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how to copy one hashmap content to another hashmap

By Chaitanya Singh

In this tutorial we are gonna learn how to copy one HashMap elements to another HashMap. We will be using putAll() method of HashMap class to perform this operation. Complete code as follows:

import java.util.HashMap;
class HashMapDemo{ 
  public static void main(String[] args) {
     // Create a HashMap
     HashMap<Integer, String> hmap = new HashMap<Integer, String>();
 
     //add elements to HashMap
     hmap.put(1, "AA");
     hmap.put(2, "BB");
     hmap.put(3, "CC");
     hmap.put(4, "DD");
 
     // Create another HashMap
     HashMap<Integer, String> hmap2 = new HashMap<Integer, String>();
 
     // Adding elements to the recently created HashMap
     hmap2.put(11, "Hello");
     hmap2.put(22, "Hi");
 
     // Copying one HashMap "hmap" to another HashMap "hmap2"
     hmap2.putAll(hmap);
 
     // Displaying HashMap "hmap2" content
     System.out.println("HashMap 2 contains: "+ hmap2);
  }
}

Output:

HashMap 2 contains: {1=AA, 2=BB, 3=CC, 4=DD, 22=Hi, 11=Hello}

All the elements of HashMap 1 got copied to the HashMap 2. putAll() operation does not replace the existing elements of Map rather it appends the elements to them.

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Comments

  1. Tanu says

    The following lines should be:

    / Adding elements to the recently created HashMap
    hmap2.put(11, “Hello”);
    hmap2.put(22, “Hi”);

    instead of the following:
    // Adding elements to the recently created HashMap
    hmap.put(11, “Hello”);
    hmap.put(22, “Hi”);

    I know this is a very small thing, but as your post says it is for beginner’s I guess everything should be correct.