.putIfAbsent()

The .putIfAbsent() method in Java adds a key-value pair to a map if the key isn’t already there. If the key exists, it returns its associated value, showing no new addition. If the key is not present, it adds the pair to the map and returns null.

Syntax

map.putIfAbsent(key, value)

• key: It is the key to be inserted into the map.
• value: It is the value associated with the key.

Example

The following Java program demonstrates the .putIfAbsent() method:

import java.util.*;

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

        // Creating a HashMap
        Map<Integer, String> map = new HashMap<>();

        // Adding some key-value pairs
        map.put(1, "apple");
        map.put(2, "banana");
        map.put(3, null); // Adding a key with a null value

        // Using putIfAbsent method
        String value1 = map.putIfAbsent(4, "orange");
        System.out.println("Value for key 4: " + value1);

        String value2 = map.putIfAbsent(2, "grape");
        System.out.println("Value for key 2: " + value2);

        String value3 = map.putIfAbsent(3, "pear");
        System.out.println("Value for key 3: " + value3);

        System.out.println("Updated Map: " + map);
    }
}

The output of the above code is as follows:

Value for key 4: null
Value for key 2: banana
Value for key 3: null
Updated Map: {1=apple, 2=banana, 3=pear, 4=orange}