ExecutorService

ExecService.java

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ForkJoinPool;

public class Main {
    public static void main(String[] args) {
        ExecutorService s = Executors.newFixedThreadPool(2);
//        System.out.println(Runtime.getRuntime().availableProcessors());
//        ForkJoinPool fk = (ForkJoinPool) Executors.newWorkStealingPool();


        Runnable task1 = () -> {
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName());
        };

        Runnable task2 = () -> {
            try {
                Thread.sleep(2000);
                System.out.println(Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        };

        Runnable task3 = () -> {
            try {
                Thread.sleep(2000);
                System.out.println(Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        };

        Runnable task4 = () -> {
            try {
                Thread.sleep(2000);
                System.out.println(Thread.currentThread().getName());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        };

        CompletableFuture c = CompletableFuture.runAsync(task1, s);

        s.submit(task2);
        s.submit(task3);

        try {
            if (c.isDone()) {
                System.out.println(c.get());
            }
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }



        System.out.println(fact(29));
        Long startTime = System.currentTimeMillis();

/*
        fk.submit(() -> {
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        fk.submit(() -> System.out.println(fact(29)));
*/
        Long endTime = System.currentTimeMillis();

//        System.out.println((endTime - startTime) / 1000);


    }

    public static int fact(int n) {
        if (n == 0 || n == 1) {
            return 1;
        }
        return n * fact(n - 1);
    }
}