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import java.util.stream.Stream;
import java.util.stream.Collectors;
import java.util.Optional;

public class OptionalStream {
 public static void main(String args[]){
    Stream<Optional<Integer>> optStreams = Stream.of(Optional.of(1), Optional.empty(), Optional.of(2), Optional.of(3));

    System.out.println(optStreams
            .flatMap(o -> o.isPresent() ?  Stream.of(o.get() * 2) : Stream.empty())
            .reduce(0, (acc, n) -> acc + n));
 }
}