Why cannot I return void from a void function

Question

Why does this code work

void hello()
{
hello();
return;
}

while this does not

void hello(){return hello();}

Error:

java.java:13: error: incompatible types: unexpected return value
return hello();

(Please ignore the logical error)

The main question: Why cannot we return void to a void function?

Does Java by any means provide support another type of void, maybe a wrapper class called Void?

_"Why does this code work"_ It doesn't really "work" as it creates an infinite recursion and finally a StackOverflowException. ;) — Markus Kauppinen, Apr 03 '20 at 14:58

score 1 · Answer 1 · answered Apr 03 '20 at 14:31

1

he main question: Why cannot we return void to a void function?

Because void function does not return a value thus you cannot return anything. In void method context return; is just "finish method execution" or "quit method", not "return nothing";

answered Apr 03 '20 at 14:31

Antoniossss

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Is there any way to return void in a void function? To support one-liner return control statements? – Mohit Shetty Apr 03 '20 at 14:33
*To support one-liner control statments*? Than maybe you should use `boolean` as return value. – Antoniossss Apr 03 '20 at 14:34
The function on which I am trying it is the main function... – Mohit Shetty Apr 03 '20 at 14:34
And you are out of luck, `void methods` does not return values. – Antoniossss Apr 03 '20 at 14:35

score 1 · Answer 2 · answered Apr 03 '20 at 14:37

1

As for one-liners, try this:

void hello() { hello(); }

istead of

void hello() { return hello(); }

answered Apr 03 '20 at 14:37

Usagi Miyamoto

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Sorry for being unclear the main function would be an conditional return and there would be other statements ahead. – Mohit Shetty Apr 03 '20 at 14:44

Andrew Tobilko · Accepted Answer · 2020-04-03T14:55:37.423

1

There is a way

class A {
  Void a() {
    // ...
    return a();
  }
}

but java.lang.Void is an uninstantiable representation of the void type meaning you can't make instances out of it (and, sensibly, you aren't supposed to). Eventually, you would need to return a value, it could be a null - the only "legit" one I can think of.

It has applications with generics and the Reflection API, but I doubt it being used here for the purpose of making a recursive method fancier (?).

class A {
  Consumer<String> a() {
    return System.out::println;
  }
}

You might want to return an instance of a function that returns void. Then, a functional interface java.util.function.Consumer might be a good fit.

Actually, it could be any interface of the kind that would suit you best. For instance,

class A {
  Runnable a() {
    // ...
    return () -> a();
  }
}

edited Apr 03 '20 at 14:55

answered Apr 03 '20 at 14:37

Andrew Tobilko

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incompatible types: void cannot be converted to Void; I tried doing it in main() by returning System.out.println() – Mohit Shetty Apr 03 '20 at 14:42
Is there any to convert `void` to `Void`? – Mohit Shetty Apr 03 '20 at 14:45
@SonofStackoverflow no – Andrew Tobilko Apr 03 '20 at 14:46

score 1 · Answer 4 · answered Apr 03 '20 at 14:39

With return type void, you can not return anything but with return type, Void, you can return null e.g.

public class Main {
    public static void main(String[] args) {
        hello();
    }

    static Void hello() {
        System.out.println("Hello");
        return null;
    }
}

Output:

Hello

You can find some more uses of Void at https://www.baeldung.com/java-void-type

score 1 · Answer 5 · answered Apr 03 '20 at 14:52

Because when a method's return value is void it does not accept any parameter, even void itself.

return x; indicates that control is leaving the method and that its result is the value of x.

return; indicates that control is leaving the method without a result.

This code does not work so I guess you should not expect yours to work too.

void fun () {return void;} // does not work

Please refer to this answer.

Why cannot I return void from a void function

5 Answers5