Kotlin Tutorials

Kotlin Map contains()
Syntax & Examples

Syntax of Map.contains()

The syntax of Map.contains() extension function is:

operator fun <K, V> Map<out K, V>.contains(key: K): Boolean

This contains() extension function of Map checks if the map contains the given key.


✐ Examples

1 Check if map contains specified key (present)

In this example,

  • We create a map named map1 containing pairs of numbers and characters.
  • We then use the in operator to check if the key 2 is present in map1.
  • As 2 is present in the keys of map1, true is printed to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val map1 = mapOf(1 to 'a', 2 to 'b', 3 to 'c')
    val containsKey1 = 2 in map1
    println(containsKey1)
}

Output

true

2 Check if map contains specified key (not present)

In this example,

  • We create a map named map2 containing pairs of characters and numbers.
  • We then use the in operator to check if the key 'd' is present in map2.
  • As 'd' is not present in the keys of map2, false is printed to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val map2 = mapOf('a' to 1, 'b' to 2, 'c' to 3)
    val containsKey2 = 'd' in map2
    println(containsKey2)
}

Output

false

3 Check if map contains specified key (present)

In this example,

  • We create a map named map3 containing pairs of strings and numbers.
  • We then use the in operator to check if the key 'banana' is present in map3.
  • As 'banana' is present in the keys of map3, true is printed to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val map3 = mapOf("apple" to 1, "banana" to 2, "cherry" to 3)
    val containsKey3 = "banana" in map3
    println(containsKey3)
}

Output

true

Summary

In this Kotlin tutorial, we learned about contains() extension function of Map: the syntax and few working examples with output and detailed explanation for each example.