In this section, you will learn the different syntax of how to define a function in Kotlin. To create your own function, use the fun keyword, and write the function name, followed by parentheses. You can use predefined functions, create your own functions, or call a function.
Predefined Functions
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| fun main() {
println("Hello World")
}
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Create Your Own Functions
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| fun myFunction() {
println("I am learning Kotlin functions.")
}
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Call a Function
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| fun main() {
myFunction()
}
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Function Parameters
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| fun myFunction(fname: String) {
println(fname + " Doe")
}
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Return Values
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| fun max(a: Int, b: Int): Int {
return if(a > b) a else b
}
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Shorter syntax for return values.
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| fun max(a: Int, b: Int): Int = if(a > b) a else b
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If you try to omit the type for a function with expression body, it will mean that this function returns Unit. You can consider of Unit as void in Java.
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| fun displayMax(a: Int, b: Int) = println(max(a, b))
// An equivalent syntactic form
fun displayMax(a: Int, b: Int): Unit = println(max(a, b))
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Kotlin Function Types
In Kotlin, you can define functions everywhere. You can define a function at the top-level or make it a member of a class. You can even define function inside another function, then it’s called a local function.
Top-level function
You call it as a static function of the class, which name corresponds to the file name.
@JVMName changes the JVM name of the class containing top-level functions.
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| // Extension.kt
@file:JvmName("Util")
package intro
fun foo() = 0
// It is used from Java like Util.foo()
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Member function
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| class A {
fun member() = 2
}
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Local function
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| fun other() {
fun local() = 3
}
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Named & Default Arguments
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| println(listOf('a','b','c').joinToString(separator = "", prefix = "(", postfix = ")"))
// output is (abc)
println(listOf('a','b','c').joinToString(postfix = "."))
// output is a,b,c. (default separator is comma ,)
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You can either provide another value or use a default one.
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| fun displaySeparator(character: Char = '*', size: Int = 10) {
repeat(size){
print(character)
}
}
displaySeparator('#', 5) // #####
displaySeparator('#') // ##########
displaySeparator() // **********
displaySeparator(size = 5) // *****
displaySeparator(size = 3, character = '5') // 555
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I’ve tried to explain the functions in Kotlin language. I will present examples about control structures.
