Optional or() method in Java with examples

The or() method of java.util.Optional class in Java is used to get this Optional instance if any value is present. If there is no value present in this Optional instance, then this method returns an Optional instance with the value generated from the specified supplier.

Syntax:

public Optional<T> or(Supplier<T> supplier)

Parameters: This method accepts supplier as a parameter of type T to generate an Optional instance with the value generated from the specified supplier.

Return supplier: This method returns this Optional instance, if any value is present. If there is no value present in this Optional instance, then this method returns an Optional instance with the value generated from the specified supplier.

Exception: This method throws NullPointerException if the supplying function is null or produces a null result.

Below programs illustrate or() method:

Note: As this method was added in Java 9, the programs need JDK 9 to execute.

Program 1:

// Java program to demonstrate
// Optional.or() method

import java.util.*;
import java.util.function.*;

public class GFG {

    public static void main(String[] args)
    {

        // create a Optional
        Optional<Integer> op
            = Optional.of(9455);

        // print supplier
        System.out.println("Optional: "
                           + op);

        // or supplier
        System.out.println("Optional by or(() ->"
                           + " Optional.of(100)) method: "
                           + op.or(() -> Optional.of(100)));
    }
}

Output:

Optional: Optional[9455]
Optional by or(() -> Optional.of(100)) method: Optional[9455]

Program 2:

// Java program to demonstrate
// Optional.or() method

import java.util.*;
import java.util.function.*;

public class GFG {

    public static void main(String[] args)
    {

        // create a Optional
        Optional<Integer> op
            = Optional.empty();

        // print supplier
        System.out.println("Optional: "
                           + op);

        try {

            // or supplier
            System.out.println("Optional by or(() ->"
                               + " Optional.of(100)) method: "
                               + op.or(() -> Optional.of(100)));
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

Output:

Optional: Optional.empty
Optional by or(() -> Optional.of(100)) method: Optional[100]

Reference: https://docs.oracle.com/javase/9/docs/api/java/util/Optional.html#or-java.util.function.Supplier-