如何添加两个Optional<Long> 在 Java 中

Question

Optional<Long>totalLanding= ....(get it from somewhere);
Optional<Long>totalSharing = ...(get it from somewhere);

I want to do something like this not syntactically but logically

Optional<Long>total = totalLanding+totalSharing;

Such that if both are empty then total should be empty if one of them has the value then total should have that value is both of them have the value then they should get added and stored in total

Answer 1

How about using Stream s?

Optional<Long> total = Stream.of(totalLanding,totalSharing)
                             .filter(Optional::isPresent)
                             .map(Optional::get)
                             .reduce(Long::sum);

BTW, I'd use OptionalLong instead of Optional<Long> .

The solution would be similar:

OptionalLong total = Stream.of(totalLanding,totalSharing)
                           .filter(OptionalLong::isPresent)
                           .mapToLong(OptionalLong::getAsLong)
                           .reduce(Long::sum);

Answer 2

Java 9 or newer:

Optional<Long>total = Stream.concat(
        totalLanding.stream(),
        totalSharing.stream())
    .reduce(Long::sum)

Java 8 compatible variant:

Optional<Long>total = Stream.concat(
        totalLanding.map(Stream::of).orElseGet(Stream::empty),
        totalSharing.map(Stream::of).orElseGet(Stream::empty))
    .reduce(Long::sum)

Or better to extract the .map(Stream::of).orElseGet(Stream::empty) as a utility method and reuse. Or other variants here: How to convert an Optional<T> into a Stream<T>?

Answer 3

This should work with Java 8:

Optional<Long> total = totalLanding.map(x -> x + totalSharing.orElse(0L))
        .map(Optional::of)   // wrap it twice for the next line to find an Optional inside
        .orElse(totalSharing);

Answer 4

How about

BigDecimal zero = BigDecimal.ZERO

Optional<Long> addition = Optional.of(totalLanding.orElse(zero).add(totalSharing.orElse(zero)));

Answer 5

我们可以这样做：

Optional<Long>result = Optional.of((totalLanding != null ? totalLanding.get() : 0L) + (totalSharing != null ? totalSharing.get() : 0L));