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Text lesson

computeIfAbsent()

Example

Calculate a value for a new entry in a map.

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.computeIfAbsent("Canada", (k) -> "Toronto (" + k + ")");

    System.out.println(capitalCities);
  }
}

Definition and Usage

The computeIfAbsent() method calculates a value for a new entry based on its key. If an entry with the specified key already exists and its value is not null, the map remains unchanged.

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

Syntax

public void computeIfAbsent(K key, Function function)

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

Parameter Values

Parameter

Description

key

Required: Specifies the key for the entry.

function

Required: A Function object or lambda expression that computes the value of the entry.

The function takes one parameter, which is the key of the entry.

Technical Details

Returns:

If an entry with the specified key already exists, it returns the value of that entry; otherwise, it returns the value computed by the function.