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.