Java Hashmap putAll() Method

import java.util.*;

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

        // Creating an empty HashMap
        HashMap < String, Integer > hash_map_1 =
                new HashMap < String, Integer > ();


        // Mapping string values to int keys in a empty hashmap
        hash_map_1.put ("Maths", 80);
        hash_map_1.put ("English", 75);
        hash_map_1.put ("Hindi", 85);
        hash_map_1.put ("Science", 90);

        System.out.println("Original hashmap : " + hash_map_1);


       //copying mapping of existing hashmap to new hashmap
        HashMap < String, Integer > new_hashmap = new HashMap < String, Integer >() ;

        new_hashmap.putAll(hash_map_1);

        System.out.println("New hashmap : "+ new_hashmap);

   }
}