computeIfPresent()

Example

Compute a new value for an existing entry in a map if the entry’s key is present and its current value is not null.

import java.util.HashMap;

public class Main {
  public static void main(String[] args) {
    HashMap<String, String> capitalCities = new HashMap<String, String>();
    capitalCities.put("England", "London");
    capitalCities.put("Germany", "Berlin");
    capitalCities.put("Norway", "Oslo");
    capitalCities.put("USA", "Washington DC");

   capitalCities.computeIfPresent("England", (k, v) -> v + "(" + k + ")");

    System.out.println(capitalCities);
  }
}

Definition and Usage

The computeIfPresent() method computes a value for an entry based on its key. If an entry with the specified key does not exist or its value is null, the map remains unchanged.

The value is computed using a function, which can be defined with a lambda expression compatible with Java’s BiFunction interface’s apply() method.

Syntax

public void computeIfPresent(K key, BiFunction function)

K represents the data type of the map’s keys.

Parameter Values

Technical Details