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Java HashMap clone()

The Java HashMap clone() method makes the shallow copy of the hashmap and returns it.

Here, the shallow copy means the keys and values are not copied. Instead, references to keys/values are copied. To learn more about the shallow copy, visit Java Shallow Copy.

The syntax of the clone() method is:

hashmap.clone()

Here, hashmap is an object of the HashMap class.


clone() Parameters

The clone() method does not take any parameters.


clone() Return Value

  • returns a copy of the HashMap instances (objects)

Example 1: Make a Copy of HashMap

import java.util.HashMap;

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

        // create HashMap
        HashMap<String, Integer> languages = new HashMap<>();

        languages.put("Java", 14);
        languages.put("Python", 3);
        languages.put("JavaScript", 1);
        System.out.println("HashMap: " + languages);

        // create copy of languages
        HashMap<String, Integer> cloneLanguages = (HashMap<String, Integer>)languages.clone();
        System.out.println("Cloned HashMap: " + cloneLanguages);
    }
}

Output

HashMap: {Java=14, JavaScript=1, Python=3}
Cloned HashMap: {Java=14, JavaScript=1, Python=3}

In the above example, we have created an hashmap named languages. Notice the expression,

(HashMap<String, Integer>)languages.clone()

Here,

  • languages.clone() - returns a copy of the object languages
  • (HashMap<String, Integer>) - converts object returned by clone() into a hashmap of String type key and Integer type values (To learn more, visit Java Typecasting)

Example 2: Print the Return Value of clone()

import java.util.HashMap;

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

        // create a hashmap
        HashMap<String, Integer> primeNumbers = new HashMap<>();
        primeNumbers.put("Two", 2);
        primeNumbers.put("Three", 3);
        primeNumbers.put("Five", 5);
        System.out.println("Numbers: " + primeNumbers);

        // print the return value of clone()
        System.out.println("Return value of clone(): " + primeNumbers.clone());
    }
}

Output

Prime Numbers: {Five=5, Two=2, Three=3}
Return value of clone(): {Five=5, Two=2, Three=3}

In the above example, we have created an hashmap named primeNumbers. Here, we have printed the value returned by clone().

Note: The clone() method is not specific to the HashMap class. Any class that implements the Clonable interface can use the clone() method.