CODEWITHSUNDEEP
kotlincompletable-future
Valeriy K.
Valeriy K.

Reputation: 2904

Concurrency Future syntax in Kotlin

I use simple java code for Future:

Future<Integer> futureTask = executor.submit(() -> {
    System.out.println("I'm Callable task.");
    return 1 + 1;
});

when I paste it to kotlin class it transforms to : 

val futureTask = executor.submit {
    println("I'm Callable task.")
    1 + 1
}

but when I try to get a value as in Java class I`m got null instead number

val integ = futureTask.get()

when I write return as in java code my ide warns that return is not allowed here.

Full kotlin code is next:

fun main(args: Array<String>) {
   val executor = Executors.newSingleThreadExecutor()
   val futureTask = executor.submit {
       println("I'm Callable task.")
       1 + 1
   }

   println(futureTask.get())
   executor.shutdown() }

Output:

I'm Callable task.
null

What is a right syntax for Future?

Upvotes: 4

Views: 1802

Answers (1)

clemp6r
clemp6r

Reputation: 3723

That is because there are two submit methods in ExecutorService and the wrong one is used.

<T> Future<T> submit(Callable<T> task);

Future<?> submit(Runnable task);

Your lambda function is translated to a Runnable instead of Callable. You can workaround this as following:

val futureTask = executor.submit(Callable {
    println("I'm Callable task.")
    1 + 1
})

Upvotes: 5

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