Kotlin

fun main() {
    println("Hello, Kotlin!")
}

val x = 10       // konstans, nem módosítható
var y = 5        // változó, módosítható

val name: String = "Dani"
val age: Int = 25
val pi: Double = 3.14

val max = if (a > b) a else b

when (x) {
    1 -> println("Egy")
    2 -> println("Kettő")
    else -> println("Más")
}

for (i in 1..5) println(i)

while (x < 10) {
    x++
}

fun add(a: Int, b: Int): Int {
    return a + b
}

fun add(a: Int, b: Int) = a + b

fun greet(name: String = "Világ") {
    println("Helló, $name!")
}

greet()           // Helló, Világ!
greet("Dani")     // Helló, Dani!

class Person(val name: String, var age: Int)

val p = Person("Dani", 25)
println(p.name)

class Person(val name: String, val age: Int)

open class Animal {
    open fun speak() = println("Hangot ad")
}

class Dog : Animal() {
    override fun speak() = println("Vau!")
}

data class User(val name: String, val age: Int)

val u1 = User("Dani", 30)
println(u1.copy(age = 31))  // másolat új értékkel

val list = listOf(1, 2, 3, 4)
val doubled = list.map { it * 2 }

val evens = list.filter { it % 2 == 0 }
val sum = list.reduce { acc, i -> acc + i }

var name: String? = null  // lehet null

val len = name?.length    // null-safe hívás
val l = name?.length ?: 0 // Elvis-operátor (null esetén 0)

val items = listOf("alma", "banán", "körte")

for (item in items) println(item)

val numbers = mutableListOf(1, 2, 3)
numbers.add(4)

import kotlinx.coroutines.*

fun main() = runBlocking {
    launch {
        delay(1000L)
        println("Világ!")
    }
    println("Helló,")
}