Core Java™ 2 Volume II - Advanced Features, Seventh Edition

Callables and Futures

A Runnable encapsulates a task that runs asynchronously; you can think of it as an asynchronous method with no parameters and no return value. A Callable is similar to a Runnable, but it returns a value. The Callable interface is a parameterized type, with a single method call.

public interface Callable<V>
{
   V call() throws Exception;
}

The type parameter is the type of the returned value. For example, a Callable<Integer> represents an asynchronous computation that eventually returns an Integer object.

A Future holds the result of an asynchronous computation. You use a Future object so that you can start a computation, give the result to someone, and forget about it. The owner of the Future object can obtain the result ...