Void返回类型在Kotlin中意味着什么

Question

I tried to create function without returning value in Kotlin. And I wrote a function like in Java but with Kotlin syntax

fun hello(name: String): Void {
    println("Hello $name");
}

And I've got an error

Error:A 'return' expression required in a function with a block body ('{...}')

After couple of changes I've got working function with nullable Void as return type. But it is not exactly what I need

fun hello(name: String): Void? {
    println("Hello $name");
    return null
}

According to Kotlin documentation Unit type corresponds to the void type in Java. So the correct function without returning value in Kotlin is

fun hello(name: String): Unit {
    println("Hello $name");
}

Or

fun hello(name: String) {
    println("Hello $name");
}

The question is: What does Void mean in Kotlin, how to use it and what is the advantage of such usage?

Answer 1

Void is an object in Java, and means as much as 'nothing'.
In Kotlin, there are specialized types for 'nothing':

• Unit -> replaces java's void
• Nothing -> 'a value that never exists'

Now in Kotlin you can reference Void , just as you can reference any class from Java, but you really shouldn't. Instead, use Unit . Also, if you return Unit , you can omit it.

Answer 2

Void is a plain Java class and has no special meaning in Kotlin.

The same way you can use Integer in Kotlin, which is a Java class (but should use Kotlin's Int ). You correctly mentioned both ways to not return anything. So, in Kotlin Void is "something"!

The error message you get, tells you exactly that. You specified a (Java) class as return type but you didn't use the return statement in the block.

Stick to this, if you don't want to return anything:

fun hello(name: String) {
    println("Hello $name")
}