Cannot Stream average() undefined for OptionalDouble

I’m using this code but eclipse shows an error saying
stream() is undefined for the type OptionalDouble
The error shown by eclipse is

• The method stream() is undefined for the type OptionalDouble .

My code is something like this

        
        return IntStream.of(1,2,3,4,5,6)
                .asLongStream()
                .flatMap(a -> a)
                .average()
                .stream()
                .mapToLong(Math::round)
                .mapToInt(i -> (int) i)
                .findFirst()
                .orElse(-1);

I tried average().getasDouble() but that also didn’t work. How do i fix the code ?
I can do one thing Double d=average().getasDouble() then apply Math.round(d) seperately.

Is it possible to fix the code after average().stream() in functional way without error ?
When average() return OptionalDouble and that can’t be streamed by stream() , how do you go about it ?

>Solution :

OptionalDouble.stream has existed ever since Java 9. You should check your Java version.

If you are unable to use a newer version of Java for some reason, you can implement stream yourself as a static helper method. What it does is very simple.

public static DoubleStream streamOfOptional(OptionalDouble d) {
    return d.isEmpty() ? DoubleStream.empty() : DoubleStream.of(d.getAsDouble());
}

return streamOfOptional(
        IntStream.of(1,2,3,4,5,6)
            .average()
        )
        .mapToLong(Math::round)
        .mapToInt(i -> (int) i)
        .findFirst()
        .orElse(-1);