import java.util.List;

import java.util.concurrent.CompletableFuture;

import java.util.concurrent.TimeUnit;

import java.util.stream.Collectors;

import java.util.stream.Stream;

public class Main {

    static CompletableFuture<List<?>> allOf(CompletableFuture<?>... cfs) {

        return CompletableFuture.allOf(cfs)

                .thenApply(ignore -> Stream.of(cfs)

                        .map(cf -> cf.join())

                        .collect(Collectors.toList()));

    }

    public static void main(String[] args) {

        // we have 3 (or any number) of CompletableFutures

        CompletableFuture<String> cf1 = CompletableFuture.supplyAsync(() -> {sleep(); return "HELLO";});

        CompletableFuture<Integer> cf2 = CompletableFuture.supplyAsync(() -> {sleep(); return ;});

        CompletableFuture<Double> cf3 = CompletableFuture.supplyAsync(() -> {sleep(); return 20d;});

        CompletableFuture<List<?>> allOf = allOf(cf1, cf2, cf3); //we call the method we just created above

        // we can get the -already there - result either using then

        // Get result using:

        allOf.thenAccept(l -> l.forEach(System.out::println));

        // or using CompletableFuture.join() (or CompletableFuture.get())

        // OR (non-typesafe)

        String s = (String) allOf.join().get();

        Integer i = (Integer) allOf.join().get();

        Double d = (Double) allOf.join().get();

        System.out.println(s + ", " + i + ", "+ d);

        sleep(); // because default CompletableFuture Executor is a daemon-thread based executor

    }

    private static void sleep(int seconds) {

        try {

            TimeUnit.SECONDS.sleep(seconds);

        } catch (InterruptedException e) {

            e.printStackTrace();

        }

    }

}