Optional stream() method in Java with examples

The stream() method of java.util.Optional class in Java is used to get the sequential stream of the only value present in this Optional instance. If there is no value present in this Optional instance, then this method returns returns an empty Stream.

Syntax:

public Stream<T> stream()

Parameters: This method do not accept any parameter.

Return value: This method returns the sequential stream of the only value present in this Optional instance. If there is no value present in this Optional instance, then this method returns an empty Stream.

Below programs illustrate stream() method:

Note: Below programs require JDK 9 and above to execute.

Program 1:

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

import java.util.*;

public class GFG {

    public static void main(String[] args)
    {

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

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

        // get the Stream
        System.out.println("Getting the Stream:");
        op.stream().forEach(System.out::println);
    }
}

Output:

Optional: Optional[9455]
Getting the Stream:
9455

Program 2:

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

import java.util.*;

public class GFG {

    public static void main(String[] args)
    {

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

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

        try {

            // get the Stream
            System.out.println("Getting the Stream:");
            op.stream().forEach(System.out::println);
        }
        catch (Exception e) {
            System.out.println(e);
        }
    }
}

Output:

Optional: Optional.empty
Getting the Stream:

Reference: https://docs.oracle.com/javase/9/docs/api/java/util/Optional.html#stream–