putIfAbsent() method in Hashtable?The putIfAbsent method adds a key-value pair to the HashTable object if the key is not present in the map.
If the key is already present, then it skips the operation.
public V putIfAbsent(K key,V value)
If the key is already present in the map, then putIfAbsent returns the value associated with the key, and no insertion will be done.
If the key is not present in the map, the key-value pair is inserted and the method returns null.
The code below demonstrates how to use the putIfAbsent method.
import java.util.Hashtable;class Main {public static void main( String args[] ) {// create a HashtableHashtable<Integer, String> numbers = new Hashtable<>();// add key-value pairs to the Hashtablenumbers.put(1, "one");numbers.put(2, "Two");numbers.put(3, "three");System.out.println("The map is => " + numbers);System.out.println("\nTrying 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 returnedSystem.out.println("The Return value is => " + value);System.out.println("The map is => " + numbers);System.out.println("\nTrying to add (4, \"Four\") in the map ");value = numbers.putIfAbsent(4, "FOUR");// key - 4 is not already present in the map// so a new entry with the key as 4 and value as FOUR will be added// and null is returnedSystem.out.println("The Return value is => " + value);System.out.println("The map is => " + numbers);}}
In the code above:
We create a Hashtable with three entries.
We attempt to add a new entry to the Hashtable with:
The already existing key 1. In this case, the old value will be returned and the insertion will be skipped.
The new key 4. In this case, the new key-value entry will be inserted and null is returned.