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I have a list of callable objects , which I am using to generate a list of future objects. I am using ExecutorService to get the Callable tasks done concurrently and storing the result as list of Future objects. Now I want to know, is there a way so I can get the original callable object which was used to generate a given future object.

enigma
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  • I have a little difficulty understanding the question. So you would want to know the Callable object that you have used to invoke the executor service? Is it the T in Callable or the callable object in List.? – vijayakumarpsg587 Dec 31 '18 at 09:40

2 Answers2

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If you obtain your Futures by calling ExecutorService.invokeAll() you can rely on the order as is documented in the javadoc.

 * @return a list of Futures representing the tasks, in the same
 *         sequential order as produced by the iterator for the
 *         given task list, each of which has completed
Frank Neblung
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    So I am creating two separate callables and added them to callableList. After that I called, executorService.invokeall(cllableList) which returns list of Future Objects. But, I am getting the output of the callbles at random, even though the first future object should have returned the output of first callable. Can you please explain. – Lazycoder-007 Oct 09 '19 at 12:21
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The default implementation doesn't give you this functionality though you can create your own callable 

   import org.apache.commons.math3.util.Pair;

    class MyCallable implements Callable<Pair<Callable,MyObject>>{

        private MyService service;
        public String name;
        public MyCallable(MyService srevice,String name){
            this.srevice = srevice;
            this.name = name;

        }

        @Override
        public Pair<Callable,MyObject> call() throws Exception {
            return new Pair(this,service.doSomeStuff())
        }
    }

Now when you invoke the callable object in your future, you will have access to the callable object. Something like future.get().getFirst().name will work.

Reza
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