Java 9中的Optional.stream()方法有什么用途？

<strong>public Stream<T> stream()</strong>

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

<strong>[TutorialsPoint, Tutorix]
[TutorialsPoint, Tutorix]</strong>