streamproduct.java

package com.company;

import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;

class Comparison {
    // NOT TESTED!!!
    static Set<String> diff(String aa, String bb) {

        Set<String> cache = new HashSet<>();
        Set<String> diff = new HashSet<>();

        cache.addAll(Arrays.asList(aa.split(" ")));

        for (String b: Arrays.asList(bb.split(" ")))
            if (!cache.contains(b)) diff.add(b);

        return diff;
    }
}

public class Main {

    public static void main(String[] args) throws InterruptedException {

        Stream<String> xs = Arrays.stream(new String[] {"abc", "bce", "fghi", "jklm", "opqr", "tuvw", "vwxyz", "opmano", "tuvwx" });
        Stream<String> ys = Arrays.stream(new String[] {"abc", "bc", "fg", "jkl", "opqr", "tuvw", "vwxyz" });

        List<String> yss = ys.limit(1000).collect(Collectors.toList());
        xs
            .flatMap(x -> yss.stream().map(y -> "(" + x + ", " + y + ") diff:" + Comparison.diff(x, y)))
            .forEach(System.out::println);
    }

}