What is HashMap.putIfAbsent in Java?

Overview

The putIfAbsent method adds the key-value pair to the map if the key is not present in the map.

If the key is already present, then it skips the operation.

Syntax

Hashmap.putIfAbsent(key, value);

Return value

If the key is already present in the map, then the value associated with the key is returned and insertion will be skipped.

If the key is not present in the map, then the key-value pair is inserted and null is returned.

import java.util.HashMap;
class Main {
    public static void main( String args[] ) {
        
        // create a HashMap
        HashMap<Integer, String> numbers = new HashMap<>();
        // add key-value pairs to the HashMap
        numbers.put(1, "one");
        numbers.put(2, "two");
        numbers.put(3, "three");
        System.out.println("The map is => " + numbers);
        System.out.println("Trying to add (1, \"ONE\") in the map ");
        String value = numbers.putIfAbsent(1, "ONE");
        
        // key -  1 is already present in the map 
        // so the value associated with the key is returned 
        System.out.println("The value is => " + value);
        System.out.println("Trying to add (4, \"Four\") in the map ");
        value = numbers.putIfAbsent(4, "FOUR");
        
        // key - 4 is nootalready present in the map 
        // so a new entry with the key as 4 and value as FOUR will be added
        // and null is returned
        System.out.println("The value is => " + value);
        System.out.println("The map is => " + numbers);
    }
}

What is HashMap.putIfAbsent in Java?

Overview

Syntax

Return value

Code

Explanation