Concatenate two or more optional string in Java 8

Question

I have a rather simple question for you guys. In Java 8 it was introduced the Optional type. I have two objects of type Optional<String> and I want to know which is the more elegant way to concatenate them.

Optional<String> first = Optional.ofNullable(/* Some string */);
Optional<String> second = Optional.ofNullable(/* Some other string */);
Optional<String> result = /* Some fancy function that concats first and second */;

In detail, if one of the two original Optional<String> objects was equal to Optional.empty(), I want the whole concatenation to be empty too.

Please, note that I am not asking how to concatenate the evaluation of two Optionals in Java, but how to concatenate two Strings that are inside some Optional.

Thanks in advance.

Answer 1

You can stream the Optionals and reduce them with a concat.

Optional<String> first = Optional.of("foo");
Optional<String> second = Optional.of("bar");
Optional<String> result = Stream.of(first, second).flatMap(Optional::stream).reduce(String::concat);

If you are using Java 8 replace the flatMap operator with filter(Optional::isPresent).map(Optional::get).

Consider also to use the joining collectors: this will return String, not an Optional<String>.