putIfAbsent() is a built-in method defined in the HashMap class in Java. The class is available in the java.util package.
The following is the method prototype:
public V putIfAbsent(K key, V value)
A HashMap is a data structure that stores data in the form of key-value pairs. Each unique key is mapped onto one or more data values.
The putIfAbsent() method is used to insert the given key-value pair into the HashMap if the associated key is not already present or mapped onto a null value.
Its functionality is similar to the put() method of HashMaps, but with the added check described above.
The method takes the following as input arguments:
key: The key to be inserted into the HashMap.
value: The value to be associated with the provided key.
Note: The types of the key and value must match the key-value types of the HashMap.
The putIfAbsent() method may return the following:
null in case of successful insertion.
The current value associated with the key in case it already exists within the HashMap.
import java.util.HashMap;public class Main{public static void main(String args[]){// Creating a new HashMapHashMap<Integer, String> hash_map = new HashMap<>();// Mapping String values to Integer keyshash_map.put(2, "Edpresso");hash_map.put(4, "Shots");hash_map.put(6, "of");hash_map.put(8, "Dev");hash_map.put(10, "Knowledge");// Displaying the HashMapSystem.out.println("HashMap: \n" + hash_map);// Mapping new value to a new keyhash_map.putIfAbsent(3, "Concise");// Mapping new value to exisiting keyString value = hash_map.putIfAbsent(8, "Developer");// Printing current value for keySystem.out.println("\nCurrent value: \n" + value);// Displaying the Updated HashMapSystem.out.println("\nUpdated HashMap: \n" + hash_map);}}
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