How to use streams to find pairs of elements from two lists or array multiplication

Question

I have two lists of numbers and I'd like to find all possible pairs of numbers. For example, given the lists [1, 2, 3] and [3, 4] the result should be:

[(1, 3), (1, 4), (2, 3), (2, 4), (3, 3), (3, 4)] 

I know I can do this using a for loop but is there any more concise way to do it using Java 8 streams?

I tried the following, but I'm missing something as I'm getting List<Stream<int[]>> instead of List<int[]>.

public static void main(String[] args) {     List<Integer> list1 = Arrays.asList(1, 2, 3);     List<Integer> list2 = Arrays.asList(3, 4);     List<int[]> pairs = list1.stream()                              .map(i -> list2.stream()                                             .map(j -> new int[]{i, j}))                              .collect(Collectors.toList());     pairs.forEach(i -> {         System.out.println("{" + i[0] + "," + i[1] + "}");     }); } 

Answer 1

Use flatMap() method instead of map(), it will combine the streams into one. Refer : Difference Between map() and flatMap() and flatMap() example