HashMap clone() Method in Java

Last Updated : 13 Dec, 2024

The clone() method of the HashMap class in Java is used to create a shallow copy of the specified HashMap. The method returns a new HashMap that contains the same key-value mappings as the original HashMap.

Example 1: Here, we will use the clone() method to clone a HashMap of Integer keys and String values.

Java

// Mapping String values to Integer keys
import java.util.HashMap;

public class GFG {
    public static void main(String[] args) {
      
        // Create a HashMap and add 
        // key-value pairs
        HashMap<Integer, String> hm = new HashMap<>();
        hm.put(1, "Java");
        hm.put(2, "C++");
        hm.put(3, "Python");

        // Print the original HashMap
        System.out.println("Original HashMap: " + hm);

        // Clone the HashMap
        HashMap<Integer, String> cl = 
          (HashMap<Integer, String>) hm.clone();

        // Print the cloned HashMap
        System.out.println("Cloned HashMap: " + cl);
    }
}

Output

Original HashMap: {1=Java, 2=C++, 3=Python}
Cloned HashMap: {1=Java, 2=C++, 3=Python}

Explanation: In the above example, the clone() method creates a shallow copy of the HashMap. Both “hm” and “cl” contain the same key-value pairs.

To know more about Shallow copy and Deep copy refer this article: Shallow copy and Deep copy.

Syntax of HashMap clone() Method

public Object clone()

Parameters: The method does not take any parameters.
Return Value: The clone() method returns a shallow copy of the HashMap.

Points to Remember:

The clone is shallow means the keys and values themselves are not cloned, but references to them are copied.
Changes to mutable objects inside the HashMap will reflect in both the original and the cloned HashMap.

Example 2: Here, we will use the clone() method to clone a HashMap of String keys and Integer values.

Java

// Mapping Integer Values to String Keys 
import java.util.*;

public class GFG {
    public static void main(String[] args) {
      
        // Creating an empty HashMap
        HashMap<String, Integer> hm = new HashMap<String, Integer>();

        // Mapping string keys to integer values
        hm.put("Java", 1);
        hm.put("C++", 2);
        hm.put("Python", 3);

        // Print and display the HashMap
        System.out.println("Original HashMap: " + hm);

        // Clone the HashMap
        HashMap<String, Integer> cl 
          = (HashMap<String, Integer>) hm.clone();

        System.out.println("Cloned HashMap: " + cl);
    }
}

Output

Original HashMap: {Java=1, C++=2, Python=3}
Cloned HashMap: {Java=1, C++=2, Python=3}

Important Points:

The same operation can be performed with any type of mappings with variation and combination of different data types.
clone() method does the shallow copy. But here the values in the original and cloned hashmap will not affect each other because primitive data type is used.