Java HashMap clone() Method Usage and Example

Java HashMap Methods

The Java HashMap clone() method creates a shallow copy of the hash table and returns it.

Here, shallow copy means not to copy the keys and values. Instead, it copies the reference to the keys/values reference.

The syntax of the clone() method is:

hashmap.clone()

clone() parameters

clone() method has no parameters.

clone() return value

• Return a copy of the HashMap instance (object)

Example1: Create a copy of HashMap

import java.util.HashMap;
class Main {
　　　　public static void main(String[] args){
　　　　　　　　//　Create a 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 a copy of languages
　　　　　　　　HashMap<String, Integer> cloneLanguages = (HashMap<String, Integer>)languages.clone();
　　　　　　　　System.out.println("Copy of HashMap: ",　+　cloneLanguages);
　　　　}
}

Output Result

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

In the above example, we created a hash map named languages. Note the expression

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

Here,

• languages.clone() - Return a copy of the object languages
  

• (HashMap<String, Integer>) - Convert the object returned by clone() to a HashMap with String type keys and Integer type values (for more information, please visitJava Type Conversion)

Example2: 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 clone() return value
　　　　　　　　System.out.println("clone() return value: ",　+　primeNumbers.clone());
　　　　}
}

Output Result

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

In the above example, we created a hash map named primeNumbers. Here, we printed the value returned by clone().

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

Java HashMap Methods