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javajava-8java-streamprimitive
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Reputation: 1251

How to collect the results of a Stream in a primitive array?

I'm trying to convert 2D list to a 2D int array. However, it seems I can only collect objects, not primitives.

When I do:

data.stream().map(l -> l.stream().toArray(int[]::new)).toArray(int[][]::new);

I get the compile-time error Cannot infer type argument(s) for <R> map(Function<? super T,? extends R>).

However, if I change int[] to Integer[], it compiles. How can I get it to just use int?

Upvotes: 26

Views: 16536

Answers (1)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726619

Use mapToInt method to produce a stream of primitive integers:

int[][] res = data.stream().map(l -> l.stream().mapToInt(v -> v).toArray()).toArray(int[][]::new);

The inner toArray call no longer needs int[]::new, because IntStream produces int[].

Demo.

Upvotes: 34

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