Future and FutureTask in java

FutureTask:

1. FutureTask is a concrete implementation of the Future, Runnable, and RunnableFuture interfaces and therefore can be submitted to an ExecutorService instance for execution.
2. When calling ExecutorService.submit() on a Callable or Runnable instance, the ExecutorService returns a Future representing the task. and one can create it manually also.
3. FutureTask acts similar to a CountDownLatch when calling get() in that it waits for the task to complete or error out.
4. Behaviour of the parameterless get() method depends on the state of the task. If tasks are not completed, get() method blocks until the task is completed. Once the task complete, it returns the result or throws an ExecutionException.
5. An overloaded variant of get() allows passing a timeout parameter to limit the amount of time the thread waits for a result.

Example :  When submitting a FutureTask instance to a thread pool (ExecutorService instance) , it returns a Future object immediately. This Future object can be used for task completion and getting result of computation asynchronously.

pool-1-thread-1
FutureTask1 output = FutureTask1 is complete
Waiting for FutureTask2 to complete
Exception: java.util.concurrent.TimeoutException
Waiting for FutureTask2 to complete
Exception: java.util.concurrent.TimeoutException
Waiting for FutureTask2 to complete
Exception: java.util.concurrent.TimeoutException
Waiting for FutureTask2 to complete
pool-1-thread-2
FutureTask2 output=FutureTask2 is complete
Both FutureTask Complete