Multiple ways to iterate Map in Kotlin with example

Map contains key and value pairs data structure.

This tutorials explains multiple ways to iterate an Map in Kotlin with examples.

Multiple ways to iterate Key and value pair in Kotlin

there are multiple ways to iterate key and value pair in Kotlin.

• use for in loop

map object in for loop iterated with each object, where each object contains key and value pairs.

Key and value pairs are printed using $variable.

fun main() {
    val map = HashMap<String, String>();
    map["1"] = "one"
    map["2"] = "two"
    map["3"] = "three"
    map["4"] = "four"
    map["5"] = "five"

    for ((key, value) in map) {
        println("$key - $value")
    }
}

Output:

1 - one
2 - two
3 - three
4 - four
5 - five

• use forEach loop

map contains forEach that iterates with callback.

Callback contains key and value that iterates and prints the values.

Here is an example

fun main() {
val map = HashMap<String, String>();
map["1"] = "one"
map["2"] = "two"
map["3"] = "three"
map["4"] = "four"
map["5"] = "five"
map.forEach { (key, value) ->
println("$key = $value")
}
}

• use Iterator function

  Map.keys return array of keys, that uses iterator to return iterator

iterator.hasNext() checks whether an element exists to iterate. iterator.next() returns next element in an array. an value for a key retrieved using Map[key] function.

Here is an example

fun main() {
val map = HashMap<String, String>();
map["1"] = "one"
map["2"] = "two"
map["3"] = "three"
map["4"] = "four"
map["5"] = "five"
val iterator = map.keys.iterator()
while (iterator.hasNext()) {
val key = iterator.next()
val value = map[key]
println("${key} - $value")
}
}

Output:

1 - one
2 - two
3 - three
4 - four
5 - five