Kotlin Cheat Sheet

Cheat sheet and tricks for the Kotlin programming language. Used to build mobile applications.

Syntax

Functions

Syntax 1

fun functionName(parameter: type): returnType = functionBody

fun circumference(radius: Double): Double = 2 * pi * radius

Syntax 2

fun functionName(parameter: type): returnType { functionBody }

fun circumference(radius: Double): Double {
    return 2 * pi * radius
}

Classes

Unlike Java, there is no need to define a setter and getter.

class className(var parameter: type) { functionBody}

class Circle(var radius: Double) {
    private val pi: Double = 3.14

    fun circumference() = 2 * pi * radius
}

val smallCircle = Circle(5.2)

Variables

val : Implicit type, null not allowed, Immutable

Like a constant.

val myName = "Nick"

var : Explicit type, null not allowed, Mutable

var myFavoriteDrink : String = "Coffee"
myFavoritDrink = "Tea" // changed the value

var + ?: Allows null, is currently null, Mutable

var whereAmI : String? = null

Print

print("$myName drinks $myFavoriteDrink")
println(" in ${whereAmI?.uppercase() ?: "No Where"}")

Nick drinks Tea in No Where