In this article, we will learn about the use of the Optional.stream() method in Java 9. First, we will learn about the optional class and its method. Then we will see the use cases along with an example.

Optional class

The Optional class was introduced in Java 8 to reduce the null pointer exception that occurs in Java. It is basically a container for the actual object that needs to be returned by a method. The point here is that if a method returns a null value, which can be null, then that method could return a value instead contained inside it. In simple words, the method will not return a null but an optional object which has a valid value or an empty.

The optional method has a number of methods to consume the values from it. We divide them into 2 parts:

The Optional.stream() Method

In Java 9, the stream() method has been added to the Optional class to improve its functionality. The stream() method can be used to transform a Stream of optional elements to a Stream of present value elements. If the Optional contains a value, then return a Stream containing the value. Otherwise, it returns an empty stream.

Syntax

public Stream<T> stream()

Uses of Optional.stream() Method

The following are the use cases of the Optional.stream() method in Java:

When you have a stream of Optional objects, you can use flatMap(Optional::stream) to filter out empty optionals and extract the present values into a new stream.
Optional.stream() allows you to use stream operations like map, filter, and reduce on the value inside an Optional when it is present.
This method helps to avoid explicit null checks by treating Optional as a container of zero or one element, which can be processed using stream operations.

Example of Optional.stream() Method

Below is an example of the Optional.stream() method in Java:

import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public class StreamMethodTest {
   public static void main(String[] args) {
      List<Optional<String>> list = Arrays.asList(
            Optional.empty(),
            Optional.of("TutorialsPoint"),
            Optional.empty(),
            Optional.of("Tutorix"));
      // If optional is non-empty, get the value in stream, otherwise return empty
      List<String> filteredListJava8 = list.stream()
            .flatMap(o -> o.isPresent() ? Stream.of(o.get()) : Stream.empty())
            .collect(Collectors.toList());
      // Optional::stream method can return a stream of either one or zero element if data is present or not.
      List<String> filteredListJava9 = list.stream()
            .flatMap(Optional::stream)
            .collect(Collectors.toList());
      System.out.println(filteredListJava8);
      System.out.println(filteredListJava9);
   }
}

Output

[TutorialsPoint, Tutorix] 
[TutorialsPoint, Tutorix]

Note: Many of the Java libraries return optional types as part of their method calls, so it is important that these optional objects can be easily integrated into the Java streams pipeline, which is heavily used by developers today optional stream method makes this integration possible.

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