Summary of some important Classes and Interfaces in java.util.concurrent package

Runnable

Intended to be more or less equivalent to starting a Thread. It defines a method that does not return anything and cannot throw checked exceptions.

Callable

A more flexible variant of the same idea. It defines a method that can return a value and throw a checked exception.

Future

Represents the result of a computation (e.g. a Callable). It is used in place of a value that may not be computed yet.

Executor

Accepts Runnables and returns void.

ExecutorService

Extends Executor to also provide a method that accepts a Callable and returns a Future.

Executors

Provides simple methods to get common types of ExecutorService implementations.