java.util.concurrent.Future<capture#293 of ?>

[Steven Rodeo]

Apologies if this may be too basic, not sure even if this question belongs here, but when I am trying to submit a Runnable Task, I am not sure what should be the return value.

The following code snippet, gives the following error.

    private class runnables implements Runnable {

        private int dude;

        private runnables(int abc) {
            this.dude = abc;
        }

        public void run() {

            System.out.println(" DO SOME THING ");

        }
    }

ExecutorService def = Executors.newFixedThreadPool(2);

Future<Runnable> ldkdl = def.submit(new runnables(3838)); // What should this be ?.

found : java.util.concurrent.Future<capture#293 of ?>
required: java.util.concurrent.Future<java.lang.Runnable>
Future<Runnable> ldkdl = def.submit(new runnables(3838));
1 error

-SM

[Ireneusz Kordal]

This compiles:

  Future<?> ldkdl = def.submit(new runnables(3838)); // What should this be ?.  

[Henry Wong]

Basically, the generic type of the future object is the type to be returned from the callable (or runnable). In the case of runnable, which doesn't have a return type, you can either use the submit() method that specifies the type, or assign it to an unknown type.... ie. Future<?>.

Henry