How do I create an empty Stream in Java?

Question

In C# I would use Enumerable.Empty(), but how do I create an empty Stream in Java?

You don’t need google at all. There is exactly one address to bookmark once when starting to develop Java software, https://docs.oracle.com/javase/8/docs/api which is the official API documentation containing each package, class and member in a structure not requiring a search engine to find them. — Holger, Feb 28 '17 at 12:57
When you already know that it exists, then yes. But Java abounds with library methods that you might hope exist, but turn out not to (or not where you thought, or with the name you thought), and you could spend quite a bit of your life looking for them if you always made the API doc your first port of call. — Andrew Spencer, Feb 22 '18 at 10:16

score 186 · Accepted Answer · edited Feb 15 '17 at 14:57

186

As simple as this: Stream.empty()

edited Feb 15 '17 at 14:57

Murat Karagöz

answered Feb 15 '17 at 14:52

Eugene

17

For a specific type stream, use `Stream.empty()`, i.e `Stream.empty()` – Mugen Mar 01 '20 at 15:06
@Mugen no, you should not. Why do you think that? – Eugene Mar 01 '20 at 15:20
Because if you don't, compiler assumes the type is `Stream extends Object>`, and why won't it? – Mugen Mar 01 '20 at 15:23
1

@Mugen you need to provide an example or ask a question, this is not how type inference should work. – Eugene Mar 01 '20 at 15:25
I provided a tip, if you think I'm wrong I'll delete it as this is your answer and I don't intend to start a new discussion. – Mugen Mar 01 '20 at 15:28
I would use Stream.builder() – AdityaKapreShrewsburyBoston Aug 10 '21 at 18:40

prasad_ · Answer 2 · 2018-09-10T06:12:53.347

13

Stream<String> emptyStr = Stream.of();

emptyStr.count() returns 0 (zero).

In addition:

For a primitive stream like IntStream, IntStream.of() works in similar way (also the empty method). IntStream.of(new int[]{}) also returns an empty stream.
The Arrays class has stream creation methods which accept an array of primitives or an object type. This can be used to create an empty stream; e.g.,: System.out.println(Arrays.stream(new int[]{}).count()); prints zero.
Any stream created from a collection (like a List or Set) with zero elements can return an empty stream; for example: new ArrayList<Integer>().stream() returns an empty stream of type Integer.

edited Sep 10 '18 at 06:12

answered Apr 18 '18 at 10:35

prasad_

This is shorter than the accepted answer; it makes you wonder why `Stream.empty()` was created. – sdgfsdh Apr 18 '18 at 12:29
10

In oppposite to `Stream.empty()`, it creates empty array internally, performs null check on it etc. You can look it up in implementation. – Marcin Majkowski Apr 26 '18 at 08:50

2 Answers2