Kotlin Functions

13. Kotlin Functions 13.1 Kotlin fun 13.2 Member functions 13.3 Single Expression function 13.4 Standard Library Function 13.5 Kotlin Getter Setter

Kotlin fun

Kotlin provides a fun keyword to define functions. It can have an optional parameter and return value like other programming language.

Example without parameter

fun welcome() : String = "Welcome to this tutorial!"

Example with parameter

fun welcome(name: String) : String = "Welcome to this $name!"

In Kotlin, each parameter is in the form of name: type and separated by a comma. Each parameter must have a return type. If the function does not return any useful value, then Unit is defined as the return type.

fun example(str: String): Unit {
	println(str)
}

In the above example, Unit return type omits the procedure-style syntax error. This is also optional, we can write the above code as -

fun main(args : Array<String>)  { 
	example("Hello World!")
}
fun example(str: String) {
	println(str)
}

Output

Hello World!

Kotlin Member functions

The function defined inside a class, object or interface is called member functions. It is invoked using the name of the class or object instance with the dot operator.

fun main(args : Array<String>)  { 
	example("Hello World!")	
}
fun example(str: String): Unit {
	println(str)
}

Output

Hello World!

Single Expression function

The single expression function is referred as one line or single line function. Such a function has shortened syntax, as it omits the braces and return type. It uses the equal to operator (=) instead of the return keyword.

fun main(args : Array<String>)  { 
	add(11)
}
fun add(i: Int) = print($i + $i)

Output

22

Standard Library Function

Kotlin has rich set of built in functions that make our development so easy. The kotlin functions cover all small to small and large to large tasks manipulations.

The below example contains two standard library functions - main() and println().

Example

fun main(args : Array<String>)  { 
    println("Welcome to Kotlin Tutorial!")
}

Kotlin Getter Setter

In Kotlin, getter and setter are methods to get and set values of properties.

Example

class Account {
	var name: String = 'Account Name'
	
	getName() = field
	
	setName(value)	=	field
}

In Kotlin, the getName() method gets the field property and the setName() method sets the field value.