Java Hashmap replace() Method

June 3, 2023

Methods in Java

A method is a group of code or set of code which is used perform a certain task. We do not need to write code again and again , instead of writing the code we can use these methods. There are two types of methods in java ‘user defined’ and ‘Inbuilt’ methods. The Hashmap class in java also have some inbuilt methods, one of those method is Java Hashmap replace() Method.

To know more about Hashmap replace() Method read the complete article

Java Hashmap replace() Method

The hashmap replace() method is used to replace the value mapped to the specified key. This method returns the old value and map the new value to the key. Below in this page you can find it’s syntax, return values, parameters with detailed examples.

Syntax :

hashmap.replace(Object key , Object value);

Parameters This method takes one parameter.
Object key : Key whose mapping value is to be replace in the hashmap.
Object value : new value which is to be mapped with the key.

Return values :

Value which is mapped to the specified key.
null : If the key is not present in the hashmap.

HashMap putall()

HashMap putifabsent()

HashMap remove()

HashMap size()

HashMap values()

Hashmap replace() Method Examples

Example 1 :

Run

import java.util.*;

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

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


        // Mapping string values to int keys in a empty hashmap
        hash_map_1.put (10, "Java");
        hash_map_1.put (20, "Hashmap");
        hash_map_1.put (25, "Replace");
        hash_map_1.put (30, "method");


        //replacing the value mapped to key 20
        String replaced= hash_map_1.replace(20,"Python");

        System.out.println ("old value mapped to key 20 is : " + replaced);
        System.out.println("new value mapped to key 20 is : "+ hash_map_1.get(20));


    }
}

Output :

old value mapped to key 20 is : Hashmap
new value mapped to key 20 is : Python

What happened above : In the above example a hashmap is created, initially which is empty and elements are inserted in hash_map_1. hash_map_1.replace(20,"Python") is called which gives 'Hashmap' as return value and mapp the new value "Python" to the key.

Example 2 :

Run

import java.util.*;

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

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


        // Mapping string values to int keys in a empty hashmap
        hash_map_1.put (10, "Java");
        hash_map_1.put (20, "Hashmap");
        hash_map_1.put (25, "Remove");
        hash_map_1.put (30, "method");


        //replacing the value mapped to key 35
        
        String replaced= hash_map_1.replace(35,"Python");

        System.out.println ("old value mapped to key 35 is : " + replaced);
        System.out.println("new value mapped to key 35 is : "+ hash_map_1.get(35));


    }
}

Output :

old value mapped to key 35 is : null
new value mapped to key 35 is : null

What happened above : In the above example a hashmap is created and key/values pair are inserted . Then hash_map_1.replace(35."Python") is called which gives null as return value because the key 35 is not mapped to any value in tha hash_map_1.

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Java Hashmap replace() Method

Methods in Java

Java Hashmap replace() Method

Syntax :

Return values :

Hashmap replace() Method Examples

Example 1 :

Output :

Example 2 :

Output :

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