Can there be additional classes in Java that implement the Future interface, and what are they called?

Yes, in Java, besides the standard Future interface, there are additional classes and interfaces that implement or extend the functionality of Future.

The main ones are:

• FutureTask — a class that implements the RunnableFuture interface, which extends Future and Runnable. It allows running asynchronous tasks and obtaining the result.

• CompletableFuture — extends Future and provides a more powerful API for asynchronous programming, including chaining calls, exception handling, and combining multiple tasks.

• RunnableFuture — an interface that combines Runnable and Future, used for tasks that can be run and have a result.

Example of using FutureTask:

Callable<Integer> callable = () -> {
    Thread.sleep(1000);
    return 123;
};

FutureTask<Integer> futureTask = new FutureTask<>(callable);
new Thread(futureTask).start();

Integer result = futureTask.get(); // blocks until the result is available
System.out.println(result); // 123