The ifPresent(java.util.function.LongConsumer) method helps us to perform the specified LongConsumer action the value of this OptionalLong object. If a value is not present in this OptionalLong, then this method does nothing.
Syntax:
public void ifPresent(LongConsumer action)
Parameters: This method accepts a parameter action which is the action to be performed on this Optional, if a value is present.
Return value: This method returns nothing.
Exception: This method throw NullPointerException if a value is present and the given action is null.
Below programs illustrate ifPresent(LongConsumer) method:
Program 1:
Java
// Java program to demonstrate// OptionalLong.ifPresent(LongConsumer) methodimport java.util.OptionalLong;public class GFG { public static void main(String[] args) { // create a OptionalLong OptionalLong oplong = OptionalLong.of(23456745678L); // apply ifPresent(LongConsumer) oplong.ifPresent((value) -> { value = Math.round(value * 0.19); System.out.println("Value after modification:=> " + value); }); }} |
Output: 
Program 2:
Java
// Java program to demonstrate// OptionalLong.ifPresent(LongConsumer) methodimport java.util.OptionalLong;public class GFG { public static void main(String[] args) { // create a OptionalLong OptionalLong oplong = OptionalLong.empty(); // apply ifPresent(LongConsumer) oplong.ifPresent((value) -> { value = value * 132435; System.out.println("Value:=> " + value); }); System.out.println("As OptionalLong is empty value" + " is not modified"); }} |
Output: 
References: https://docs.oracle.com/javase/10/docs/api/java/util/OptionalLong.html#ifPresent(java.util.function.LongConsumer)