Java program to update value of HashMap using key

HashMap is a part of the Java Collections Framework, and it is used for storing key-value pairs. In this article, we will see how to update the value of a HashMap using a key.

We will use following methods to update the value of a HashMap:

• Using put() Method
• Using compute() Method
• Using replace() Method

Using put() Method

The put() method is used to add a key-value pair to the HashMap. If the key already exists, it will update the value that is stored with that key.

Example

In the following example, we will create a HashMap and then update the value of a key using the put() method.

import java.util.HashMap;
import java.util.Map;
public class UpdateHash {
   public static void main(String[] args) {
      HashMap<String, Integer> map = new HashMap<>();
      map.put("Apple", 10);
      map.put("Banana", 20);
      map.put("Cherry", 30);
      
      System.out.println("Original Map: " + map);
      
      map.put("Banana", 25);
      
      System.out.println("Updated Map: " + map);
   }
}

Output

Following is the output of the above code:

Original Map: {Apple=10, Banana=20, Cherry=30}
Updated Map: {Apple=10, Banana=25, Cherry=25}

Using compute() Method

The compute() method is from the Map interface, and it is used for computing a new value for a key based on its current value. If the key does not exist, it will add the key with the computed value.

Example

In the following is the code to update the value of a HashMap using the compute() method.

import java.util.HashMap;
import java.util.Map;
public class UpdateHash {
   public static void main(String[] args) {
      HashMap<String, Integer> map = new HashMap<>();
      map.put("Apple", 10);
      map.put("Banana", 20);
      map.put("Cherry", 30);
      
      System.out.println("Original Map: " + map);
      
      map.compute("Banana", (key, value) -> value + 5);
      
      System.out.println("Updated Map: " + map);
   }
}

Output

Following is the output of the above code:

Original Map: {Apple=10, Banana=20, Cherry=30}
Updated Map: {Apple=10, Banana=25, Cherry=30}

Using replace() Method

Another way to update the value of a HashMap is to use the replace() method. If the key exists, it will update the value with the new value provided.

Example

In the following is the code to update the value of a HashMap using the replace() method.

import java.util.HashMap;
import java.util.Map;
public class UpdateHash {
   public static void main(String[] args) {
      HashMap<String, Integer> map = new HashMap<>();
      map.put("Apple", 10);
      map.put("Banana", 20);
      map.put("Cherry", 30);
      
      System.out.println("Original Map: " + map);
      
      map.replace("Banana", 25);
      
      System.out.println("Updated Map: " + map);
   }
}

Output

Following is the output of the above code:

Original Map: {Apple=10, Banana=20, Cherry=30}
Updated Map: {Apple=10, Banana=25, Cherry=30}