How to implement the Elvis operator in Java 8?

Question

I have the classic "Elvis operator" case, where I'm calling methods that each may return null and chaining them together:

thing?:nullableMethod1(a)?:nullableMethod2(b)?:nullableMethod3()

In Java 8, the most faithful implementation I've found is something like this:

return Optional.ofNullable(thing)
    .flatMap(x -> Optional.ofNullable(x.nullableMethod1(a)))
    .flatMap(y -> Optional.ofNullable(y.nullableMethod2(b)))
    .flatMap(z -> Optional.ofNullable(z.nullableMethod3()))

I wish that Java's Optional had something akin to the elvis operator:

public<U> Optional<U> elvisOperator(Function<? super T, ? extends U> mapper) {
    return flatMap(t -> Optional.ofNullable(mapper.apply(t));
}

So that I wouldn't have to wrap each return value:

return Optional.ofNullable(thing)
    .elvisOperator(x -> x.nullableMethod1(a))
    .elvisOperator(y -> y.nullableMethod2(b))
    .elvisOperator(Z::nullableMethod3); // also nice

Is there a more efficient and idiomatic way to implement the Elvis operator pattern in Java 8?

Answer 1

Maybe I'm overlooking something, but is there a reason that you can't use Optional#map?

The following example prints nothing, as Optional is short-circuiting in the sense that, if the value inside the Optional doesn't exist (it's null or the Optional is empty), it's treated as empty.

Optional.ofNullable("test")
        .map(s -> null)
        .ifPresent(System.out::println);

For that reason, I'd think you could just do the following:

return Optional.ofNullable(thing)
               .map(x -> x.nullableMethod1(a))
               .map(y -> y.nullableMethod2(b))
               .map(Z::nullableMethod3);

This would map your thing if it exists, or return an empty Optional otherwise.