A task that returns a result and may throw an exception.
Implementors define a single method with no arguments called
Callable interface is similar to
Runnable, in that both are designed for classes whose
instances are potentially executed by another thread. A
Runnable, however, does not return a result and cannot
throw a checked exception.
Executors class contains utility methods to
convert from other common forms to
Computes a result, or throws an exception if unable to do so.