Loops

Kotlin supports all the commonly used loops: for, while, do-while

for

for in Kotlin works the same way as in most languages.

fun main(args: Array<String>) {
    val cakes = listOf("carrot", "cheese", "chocolate")
    
    for (cake in cakes) {                               // 1
        println("Yummy, it's a $cake cake!")
    }

}

1. Loops through each cake in the list.

while and do-while

while and do-while constructs work similarly to most languages as well.

fun eatACake() = println("Eat a Cake")
fun bakeACake() = println("Bake a Cake")

fun main(args: Array<String>) {
    var cakesEaten = 0
    var cakesBaked = 0
    
    while (cakesEaten < 5) {                    // 1
        eatACake()
        cakesEaten ++
    }
    
    do {                                        // 2
        bakeACake()
        cakesBaked++
    } while (cakesBaked < cakesEaten)

}

1. Executes the block while the condition is true.
2. Executes the block first and then checking the condition.

Iterators

You can define your own iterators in your classes by implementing the iterator operator in them.

class Animal(val name: String)

class Zoo(val animals: List<Animal>) {

    operator fun iterator(): Iterator<Animal> {             // 1
        return animals.iterator()                           // 2
    }
}

fun main() {

    val zoo = Zoo(listOf(Animal("zebra"), Animal("lion")))

    for (animal in zoo) {                                   // 3
        println("Watch out, it's a ${animal.name}")
    }

}

1. Defines an iterator in a class. It must be named iterator and have the operator modifier.
2. Returns the iterator that meets the following method requirements:

• next(): Animal
• hasNext(): Boolean

3. Loops through animals in the zoo with the user-defined iterator.

The iterator can be declared in the type or as an extension function.