Java: Copy all of the mappings from the specified map to another map

Last update on May 22 2025 13:15:30 (UTC/GMT +8 hours)

3. Copy Mappings to Another Map

Write a Java program to copy all mappings from the specified map to another map.

Sample Solution:-

Java Code:

import java.util.*;  
public class Example3 {  
   public static void main(String args[]) {
  // create two hash maps
  HashMap <Integer,String> hash_map1 = new HashMap <Integer,String> ();
  HashMap <Integer,String> hash_map2 = new HashMap <Integer,String> ();
  // populate hash maps
  hash_map1.put(1, "Red");
  hash_map1.put(2, "Green");
  hash_map1.put(3, "Black");
  System.out.println("\nValues in first map: " + hash_map1);
  hash_map2.put(4, "White");
  hash_map2.put(5, "Blue");
  hash_map2.put(6, "Orange");
  System.out.println("\nValues in second map: " + hash_map2);

  // put all values in secondmap
  hash_map2.putAll(hash_map1);
  System.out.println("\nNow values in second map: " + hash_map2);
 }
}

Sample Output:

Values in first map: {1=Red, 2=Green, 3=Black}                         
                                                                       
Values in second map: {4=White, 5=Blue, 6=Orange}                      
                                                                       
Now values in second map: {1=Red, 2=Green, 3=Black, 4=White, 5=Blue, 6=
Orange}

For more Practice: Solve these Related Problems:

Write a Java program to copy all entries from one HashMap to another using putAll() and then verify both maps are equal.
Write a Java program to merge two maps into a new map using Java streams and then print the merged result.
Write a Java program to implement a custom deep copy method for a map containing mutable objects.
Write a Java program to copy mappings from one map to another and then remove entries with null values from the new map.

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