CODEWITHSUNDEEP
javajava.util.concurrent
nimo23
nimo23

Reputation: 5680

use Executors.callable() within lambda

I have the following which works:

var tasks = tasks.stream(a -> (Callable<Set<FinishedTask>>) () -> call(a)).collect(Collectors.toList());

I want to change the above code to use Executors.callable

// how to cast executor.callable?
var tasks = tasks.stream(t -> (Set<FinishedTask>)Executors.callable(()-> call(t))).collect(Collectors.toList());

However, I get the compiler error:

The method callable(Runnable) is ambiguous for the type Executors

What is wrong with the cast?

Upvotes: 1

Views: 396

Answers (1)

matt
matt

Reputation: 12347

You have two issues here.

First this type of error, java cannot infer which method to call.

Callable<?> c = Executors.callable( (PrivilegedAction) () -> "tested" );

By using a cast you can tell java to use Executors.callable(PrivilegedAction) instead of Executors.callable(PrivilegedExceptionAction). They both have the same method signature. Runnable is not mistaken in this case because it is a void return type.

Second, now it will know which method to use, but it is still returning a Callable, so you cannot just cast it to a set.

Callable<Set<FinishedTask>> callable = () -> call(a);
Callable<Set<FinishedTask>> callable2 = Executors.callable(()-> call(t));

You're trying to cast to a set. You need to call.

Set<FinishedTask> sft = Executors.callable(()-> call(t)).call();

Upvotes: 2

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