Any and Unit
- Kotlin course
- Beginner
- Lesson 17/116
- 5 min
Learn Any and Unit types.
Any and Unit
Any is the supertype of all non-nullable types in Kotlin. If a variable can hold values of different types, you can use Any: val x: Any = 5 then x = "text" is valid.
Unit indicates that a function returns no value; it is Kotlin's equivalent of Java's void but is actually a type with a single instance.
fun hello(): Unit {
println("Hello")
}Practice Unit function
At the top level, write fun hello(): Unit with a println("Hello") inside. Inside fun main(), call hello().
Sample solution
fun hello(): Unit {
println("Hello")
}
fun main() {
hello()
}Expected output
Hello
The Nothing type
Nothing is Kotlin's bottom type: it represents computations that never complete. For example, an infinite loop or a function that always throws returns Nothing.
In practice, the TODO() function returns Nothing; this makes it useful to mark code not yet written. Don't confuse it with Unit: Unit does return a value (its single instance), Nothing never returns.
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Return type
fun hello(): ____ {
println("Hello")
}fun hello(): Unit {
println("Hello")
}Explanation: Unit is the type of a function that returns no value.
2 Of which types is Any the supertype?
- All non-nullable types Correct answer
- Only Int
- Only String
- Only classes
Explanation: Any is the supertype of all non-nullable types.
3 Any and Unit: match the terms
| Term | Meaning |
|---|---|
Any |
Supertype |
Unit |
No return |
Nothing |
Never returns |
Int |
Integer |