How to declare Callable to execute function returning void in Java?

Question

Suppose I would like to run static method foo asynchronously

void foo() throws Exception {...}

Since foo throws an exception I would prefer create a Callable and invoke ExecutorService.submit with it to get a Future.

Now I wonder how to declare those Callable and Future properly. Should I declare them

Callable<Void> and Future<Void>?

Yes.Callable. But void is not compatible with Void, so you have to call your foo() from a wrapper method returning Void. — Alexei Kaigorodov, Aug 29 '13 at 13:20

score 23 · Accepted Answer · answered Aug 29 '13 at 13:19

23

Should I declare them Callable<Void> and Future<Void>?

Yes.

Void is similar to the wrapper classes Integer, Long etc. for the primitive types int, long etc. You could say it's a wrapper class for void, even though void is not really a type.

answered Aug 29 '13 at 13:19

Jesper

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And as you have to return a result of type Void, your Callback#call() method has to return null. And thus, as you anyway have to return, you might use Boolean as return type and return Boolean.TRUE (or in case of an error Boolean.FALSE). So it just might have better readability. – user2777500 May 05 '14 at 14:23

score 2 · Answer 2 · answered Aug 29 '13 at 14:33

2

I think you should declare them Callable<?> and Future<?>. Then you can implement them anyway you want including Callable<Void> and Future<Void>.

answered Aug 29 '13 at 14:33

emory

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Nope, it won't work in the situation OP asked about. – Anton Jul 15 '15 at 16:04

How to declare Callable to execute function returning void in Java?

2 Answers2