Use a Java stream to connect the elements of two collections with separators

I have two ways to say:

ImmutableSet<String> firstSet = ImmutableSet.of("1","2","3");
ImmutableSet<String> secondSet = ImmutableSet.of("a","b","c");

I want to get a set that contains the elements of the first set connected to each element of the second set, and a separator, that is, the output should be:

ImmutableSet<String> thirdSet = ImmutableSet.of("1.a","1.b","1.c","2.a","2.b","2.c","3.a","3.b","3.c");

(here "." Is my separator)

I initially thought I could stream the first set and apply collectors on the second set of elements Join () to achieve this, but it doesn't solve my needs

Solution

Looks like you're using guava In this case, you can simply use sets Cartesian product method

Set<List<String>> cartesianProduct = Sets.cartesianProduct(firstSet,secondSet);
for (List<String> pairs : cartesianProduct) {
    System.out.println(pairs.get(0) + "." + pairs.get(1));
}

Output:

1.a
1.b
1.c
2.a
2.b
2.c
3.a
3.b
3.c

If you want to collect it in immutableset < string >, you can use

ImmutableSet<String> product = ImmutableSet.copyOf(
        cartesianProduct.stream()
                        .map(pairs -> pairs.get(0) + "." + pairs.get(1))
                        .toArray(String[]::new)
);