What is the Optional.orElseGet method in Java?

In Java, the Optional object is a container object which may or may not contain a value. Using the Optional object’s isPresent method, we can replace the multiple null check. The Optional class is present in the java.util package.

Read more about the Optional class here.

What is the orElseGet method of the Optional class?

The orElseGet method will return the value present in the Optional object.

If the value is not present, then the function passed as an argument is executed and the value returned from the function is returned.

public T orElseGet(Supplier<? extends T> other)

Argument

The argument is the supplier function that is to be executed if the Optional object is empty (if there is no value present in the Optional object).

Return value

If the Optional object contains a value, then the value is returned. Otherwise, the value returned from the passed argument function is returned.

This method throws NullPointerException if no value is present and the supplier function is null.

Code

The below code denotes how to use the orElseGet method.

import java.util.Optional;
  
class OptionalOrElseGetExample {
    public static void main(String[] args) {
        Optional<Integer> optional1 = Optional.of(1);
        System.out.println("Optional1 : " + optional1);
        Integer val =  optional1.orElseGet(()-> 10);
        System.out.println("Value at Optional1 is : " + val);
        Optional<Integer> optional2 = Optional.empty();
        System.out.println("\nOptional2 : " + optional2);
        val =  optional2.orElseGet(()-> 10);
        System.out.println("Value at Optional2 is : " + val);
        
    }
}

Explanation

In the above code:

  • In line number 1, we import the Optional class.
import java.util.Optional;
  • In line number 5, we create an Optional object of the Integer type with value 1 using the of method.
Optional<Integer> optional1 = Optional.of(1);
  • In line number 7, we call the orElseGe method on the optional1 object. For the orElseGet method, a function which returns 10 is passed as an argument. This method returns 1 because the optional1 object contains the value.
Integer val =  optional1.orElseGet(()-> 10);
val;// 1
  • In line number 10, we use the empty method to get an empty Optional object of the Integer type. The returned object doesn’t have any value.
Optional<Integer> optional2 = Optional.empty();
  • In line number 12, we call the orElseGe method on the optional2 object. For the orElseGet method, a function which returns 10 is passed as an argument. This method returns 10 because the optional2 object doesn’t contain any value.
val =  optional2.orElseGet(()-> 10);
val;// 10

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