Convert OptionalDouble to Optional <java.lang.Double>

Question

I have a method that builds a list and I want it to return the average of the list as an Optional value.

However, when I calculate the average value using Java 8, I always get the return value as an OptionalDouble.

How do I convert

OptionalDouble to Optional<Double>?

Below are my code for average calculation:

private static Optional<Double> averageListValue() {
     // Build list
     List<Double> testList = new ArrayList<>();
     testList.add(...);
     ...
     ...


     return testList.stream().mapToDouble(value -> value).average();
}

Thanks.

Answer 1

I'd go for this approach:

private static Optional<Double> convert(OptionalDouble od) {
    return od.isPresent() ? 
        Optional.of(od.getAsDouble()) : Optional.empty();
}

Answer 2

A slight variation on @Andremoniy's answer is to skip the DoubleStream and use the averagingDouble() collector:

if (testList.isEmpty()) {
    return Optional.empty();
}
return Optional.of(testList.stream().collect(Collector.averagingDouble()));

Or consider whether 0 is a valid return value for an empty list, and possibly skip the Optional entirely.