I'm learning Kotlin, so I have been updating it with examples and explanations about the language that I'm using at work.
Examples of projects using Kotlin:
.ktsKotlin script.ktKotlin class
There are two ways to declare variables using Kotlin: val and var.
valis a constantvarfor a variable whose value can change
Example: 01-variable.kts
It's possible use conditional statements to assign a value to variable:
val answerString: String = if (count == 42) { "I have the answer." } else if (count > 35) { "The answer is close." } else { "The answer eludes me." }We must pass params with types and every function needs return type too.
fun sum(a: Int, b: Int): Int { return a + b } // or fun sum(a: Int, b: Int) = a + bExample: 02-functions.kts
There are some ways to concatenate variables in a String
fun bestAnime(): String { return "Naruto" } print("Best Animes:" + bestAnime()) print("Best Animes: ${bestAnime()}")Example of Try-catch block for exception handling
try { val message = "Hello World! I love Digimon!" message.toInt() } catch (exception: NumberFormatException) { // ... }Instead to use getters and setters we can use properties
- Getter
class Pokemon(val name: String, val type: String) { val description: String get() = "Pokemon ${name} is ${type} type" }- Setter
var power = 0.0 set(value) { if (value > 0) { field = value } }Example: 03-properties.kts
enum class Console { GBA, PLAYSTATION, XBOX, SWITCH, PC }Example: 04-enums.kts
Creating a class using Enum
class Game(val name: String, val console: Console) { fun play(): String { return "You're playing $name on $console" } }Example: 05-classes.kt
There is some ways to create lists in Kotlin
var digimons = mutableListOf("Agumon", "Tailmon", "Angemon") var digimons = listOf("Agumon", "Tailmon", "Angemon") val digimonPower: MutableMap<Int, Int> = mutableMapOf(0 to 50, 1 to 50, 2 to 100) // Empty List var pokemons = arrayListOf<String>()When is similar Java Switch
fun getPrice(console: Console): Int = when (console) { Console.GBA -> 1000 Console.PLAYSTATION -> 5299 Console.SWITCH -> 2500 Console.XBOX -> 4200 Console.PC -> 5000 }Example: 06-when.kt
Example of how to iterate over a map
val binaryRepresentation = TreeMap<Char, String>() for (c in 'A'..'F') { val binary = Integer.toBinaryString(c.toInt()) binaryRepresentation[c] = binary } for ((letter, binary) in binaryRepresentation) { println("$letter - $binary") }Example: 08-interatingovermap.kt
It's possible to use "in" in a conditional
fun isLetter(c: Char) = c in 'a'..'z' || c in 'A'..'Z' fun isNotDigit(c: Char) = c !in '0'..'9'Example: 09-inoperation.kt
We can use Mockito, but the best lib to mock using kolint is Mockk
val car = mockk<Car>() every { car.drive(Direction.NORTH) } returns Outcome.OK car.drive(Direction.NORTH) // returns OK verify { car.drive(Direction.NORTH) } confirmVerified(car)- Learn the Kotlin programming language
- Get started with Kotlin - KotlinLang.org
- Curso de Kotlin 2020 | Básico
developed by Jean Jacques Barros