Runnable JDK 1.0 

new Thread( () -> System.out.println("Runnable") ).start()

Callbale Java 5

Callable callable = Executors.callable(Runnable task);

Callable returns Future object

call method can throw checked exception 

Future result = exec.submit(aCallable);

Response = result.get();

Callable<String> callable = () -> {

    // Perform some computation

    Thread.sleep(2000);

    return "Return some result";

};

Remember, Future.get() is a blocking method and blocks until execution is finished,

so you should always call this method with a timeout to avoid deadlock or livelock in your application

 while(!future.isDone()) {

            System.out.println("Task is still not done...");

            Thread.sleep(200);

            double elapsedTimeInSec = (System.nanoTime() - startTime)/1000000000.0;

            if(elapsedTimeInSec > 1) {

                future.cancel(true);

            }

        }        

future.get(100,TimeUnit.MILLISECONDS) :

 Method waits for the result of the task atmost 100 milliseconds, If the wait time out, then get throws TimeoutException.

(  future : future_results){

response= future.get();

}

Keep in mind future.get() will get blocked if its not completed. if future  get is in loop , it will not proceed for the next future get call.

If application receives multiple http request thread , it is prone to get all app thread blocked resulting application unresponsive.