Completed future test

CompletedFutureTest.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.stream.Collectors;

public class CompletedFutureTest {

    private static ExecutorService executor = Executors.newFixedThreadPool(3);

    public static void main(String args[]) {

        List<Integer> numbers = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));
        System.out.println("Start list 1");
        getIntegerList(numbers);
        System.out.println("End list 1");
        System.out.println("Start list 2");
        getIntegerList2(numbers);
        System.out.println("End list 2");

        executor.shutdown();
    }

    private static List<Integer> getIntegerList(List<Integer> numbers) {
        return numbers
                .stream()
                .map(
                        number ->
                                CompletableFuture.supplyAsync(
                                        () -> getNumberCalculation(number),
                                        executor
                                )
                )
                .map(CompletableFuture::join)
                .collect(Collectors.toList());
    }

    private static List<Integer> getIntegerList2(List<Integer> numbers) {
        return numbers
                .stream()
                .map(
                        number ->
                                CompletableFuture.supplyAsync(
                                        () -> getNumberCalculation(number),
                                        executor
                                )
                )
                .collect(Collectors.toList())
                .stream()
                .map(CompletableFuture::join)
                .collect(Collectors.toList());
    }


    private static int getNumberCalculation(int number) {
        try {
            TimeUnit.SECONDS.sleep(1);
            System.out.println("Number " + number + " calculated");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        return number * 2;
    }
}