在java 8中合并具有不同类型和长度的多个流

Question

How can I merge multiple streams in java 8 with different types and length

Stream<String> x = Stream.of("A", "B", "C");
Stream<Integer> y = Stream.of(3, 7);
Stream<Float> z = Stream.of(1.1f, 2.2f);

Expected result, is a steam that holds something like this:

A 3 1.1f
A 3 2.2f
A 7 1.1f
A 7 2.2f
B 3 1.1f
B 3 2.2f
B 7 1.1f
B 7 2.2f
C 3 1.1f
C 3 2.2f
C 7 1.1f
C 7 2.2f

Answer 1

You'll have to define some class that holds these 3 properties. Let's call it Triplet .

But since we have to stream over some of the sources of data multiple times, it's better to start with List s, not Stream s:

List<String> x = List.of("A", "B", "C");
List<Integer> y = List.of(3, 7);
List<Float> z = List.of(1.1f, 2.2f);

(If you must start with Stream s, you'll have to collect the second and third Stream s into List s first).

Now you can write:

Stream<Triplet> triplets =
    x.stream()
     .flatMap(a -> y.stream()
                    .flatMap (b -> z.stream()
                                    .map(c -> new Triplet(a,b,c))));

If you wish, you can make the Triplet class generic (and then produce a Stream<Triplet<String,Integer,Float>> ).

Answer 2

Since the original question used streams as input and those are not reusable, I want to add my version which converts the second and third streams to lists (with the performance penalty of list creation). If performance is an issue it would be best if you could have at least two of the streams as lists in the first place.

Also, if you want to use the org.apache.commons:commons-lang3:3.9 library you have the Triple class which can hold the result.

    List<Integer> yList = y.collect(Collectors.toList());
    List<Float> zList = z.collect(Collectors.toList());
    Stream<Triple<String, Integer, Float>> newStream =
            x.flatMap(a -> yList.stream()
                    .flatMap (b -> zList.stream()
                            .map(c -> Triple.of(a, b, c))));
    newStream.forEach(System.out::println);