Can I duplicate a Stream in Java 8?

Question

Sometimes I want to perform a set of operations on a stream, and then process the resulting stream two different ways with other operations.

Can I do this without ha

Answer 1

Either,

• Move the initialisation into a method, and simply call the method again

This has the advantage of being explicit about what you are doing, and also works for infinite streams.

• Collect the stream and then re-stream it

In your example:

final int[] arr = IntStream.range(1, 100).filter(n -> n % 2 == 0).toArray();

Then

final IntStream s = IntStream.of(arr);

Answer 2

For non-infinite streams, if you have access to the source, its straight forward:

@Test
public void testName() throws Exception {
    List<Integer> integers = Arrays.asList(1, 2, 4, 5, 6, 7, 8, 9, 10);
    Stream<Integer> stream1 = integers.stream();
    Stream<Integer> stream2 = integers.stream();

    stream1.forEach(System.out::println);
    stream2.forEach(System.out::println);
}

prints

1 2 4 5 6 7 8 9 10

1 2 4 5 6 7 8 9 10

For your case:

Stream originalStream = IntStream.range(1, 100).filter(n -> n % 2 == 0)

List<Integer> listOf = originalStream.collect(Collectors.toList())

Stream stream14 = listOf.stream().filter(n -> n % 7 == 0);
Stream stream10 = listOf.stream().filter(n -> n % 5 == 0);

For performance etc, read someone else's answer ;)