How can I make stream with fixed arguments along with varargs? [duplicate]

Question

Let's say we have the following method.

void some(int id, int... otherIds) {

}

How can I create a single IntStream with those two arguments?

IntStream.concat(
        IntStream.of(id),
        Optional.ofNullable(otherIds)
                .map(IntStream::of)
                .orElseGet(IntStream::empty)
);

It seems verbose. Do we have any concise idiom for that?

Answer 1

When you need to deal with nullable stream-source, you might use Stream.ofNullable() accessible with Java 9, which produces either a singleton-stream or an empty stream. It'll be cleaner than utilizing Optional.ofNullable() for the purpose of chaining methods on it.

IntStream.concat(IntStream.of(id),
    Stream.ofNullable(otherIds).flatMapToInt(IntStream::of))

---

Another option is to make use of Java 9 static method Objects.requireNonNullElse() which expects a nullable argument and a default value:

IntStream.concat(IntStream.of(id),
    IntStream.of(Objects.requireNonNullElse(otherIds, new int[0])))

---

And the simplest and cleanest solution will be a fail-fast implementation, that will throw a NullPointerException in case if array otherIds is null.

IntStream.concat(IntStream.of(id), Arrays.stream(otherIds))

A null-safe flavor of it (credits to @Holger):

IntStream.concat(IntStream.of(id),
                 otherIds != null ? Arrays.stream(otherIds) : IntStream.empty())

Answer 2

Well, Alexander Ivanchenko has already mentioned three options.

Here's another one:

Objects.requireNonNull(otherIds);
Stream.of(new int[] { id }, otherIds)
    .flatMapToInt(Arrays::stream)

I think otherIds should not be null, and should be considered a programmer error. With Objects::requireNonNull it fails-fast.