Java HashMap computeIfPresent() Method

Last Updated : 15 Jan, 2025

In Java, the computeIfPresent() method of the HashMap class is used to compute a new value for a specified key if the key is already present in the map and its value is not null. If the key is not present, no action is taken.

Example 1: In this example, the computeIfPresent() method updates the value of the key if it exists in the map.

Java

// Java program to demonstrates the
//  working of computeIfPresent() 
import java.util.HashMap;

public class Geeks {
    public static void main(String[] args) {
      
        // Create a HashMap and add some values
        HashMap<String, Integer> m = new HashMap<>();
        m.put("Geeks", 1);
        m.put("for", 2);
        m.put("geeks", 3);

        // print HashMap details
        System.out.println("HashMap before operation :\n" + m);

        // Update value for the key "Geeks" using computeIfPresent
        m.computeIfPresent("Geeks", (key, val) -> val + 100);

        // print new mapping
        System.out.println("HashMap after operation :\n" + m);
    }
}

Output

HashMap before operation :
{geeks=3, Geeks=1, for=2}
HashMap after operation :
{geeks=3, Geeks=101, for=2}

Explanation: The above example demonstrates the computeIfPresent() method by updating the value of the key “Geeks” in a HashMap if it exists. The value is incremented by 100, and the updated HashMap is displayed.

Syntax of computeIfPresent() Method

default V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction)

Parameters:

Key: The key whose presence in the map is to be tested.
BiFunction: A function to compute a new value for the given key.

Return Type: The new value associated with the key or null if the key was removed.

Example 2: The below Java program demonstrates that no change will occur in the map if the key is absent.

Java

// Java program to demonstrates the working of
// computeIfPresent() when the key is absent in the map
import java.util.HashMap;

public class Geeks {
    public static void main(String[] args) {
      
        // Create a HashMap and add some values
        HashMap<String, Integer> m = new HashMap<>();
        m.put("Geeks", 1);
        m.put("for", 2);
        m.put("geeks", 3);

        // print HashMap details
        System.out.println("HashMap before operation :\n" + m);

        // key "Java" is not present in the map, so no change
        m.computeIfPresent("Java", (key, val) -> val + 100);

        // print new mapping
        System.out.println("HashMap after operation :\n" + m);
    }
}

Output

HashMap before operation :
{geeks=3, Geeks=1, for=2}
HashMap after operation :
{geeks=3, Geeks=1, for=2}

Example 3: If we pass null as the remapping function, a NullPointerException will be thrown.

Java

// Java program to demonstrates 
// computeIfPresent() throws NullPointerException
import java.util.HashMap;

public class Geeks {
    public static void main(String[] args)
    {
        HashMap<String, Integer> m = new HashMap<>();
        m.put("Geeks", 10);

        // Passing null as the remapping function
        // throws NullPointerException
        m.computeIfPresent("Geeks", null);
    }
}