ExecutorService, Callable and Future

Starting a thread:

ExecutorService executor = Executors.newFixedThreadPool(3); // We start a pool of 3 threads.
// Threads exceeding these 3 will wait for a free thread in the pool 
executor.submit(() -> {
    System.out.println("Task in executor");
});

Waiting for result:

ExecutorService executor = Executors.newFixedThreadPool(3);
Future<Double> future = executor.submit(() -> {
    for (int i = 1; i <= 10; i++) { // example of long executing code
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        System.out.println("Thread iteration " + i);
    }
    return Math.random();
});

System.out.println("Result: " + future.get()); // Waiting and read result
executor.shutdown();

Example of callable:

Callable<Double> task = () -> {
    Thread.sleep(1_000);
    return Math.random();
};
Future<Double> future = Executors.newSingleThreadExecutor().submit(task);

System.out.println("Result: " + future.get());

Thread cancellation:

ExecutorService executor = Executors.newFixedThreadPool(3);
Future<Double> future = executor.submit(() -> {
    for (int i = 1; i <= 10; i++) { // example of long executing code
        try {
            Thread.sleep(1_000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        System.out.println("Thread iteration " + i);
    }
    return Math.random();
});

Thread.sleep(5_000L);
future.cancel(true); // Thread cancellation after 5 seconds

Thread.sleep(10_000L);
executor.shutdown();

Asynchronics tasks

CompletableFuture allows for asynchronous operations with the ability to combine them and handle errors:

CompletableFuture.supplyAsync(() -> "Data")
        .thenApply(data -> data + " processed")
        .thenAccept(System.out::println);