Kotlin Map containsKey()
Syntax & Examples

Syntax of Map.containsKey()

The syntax of Map.containsKey() function is:

abstract fun containsKey(key: K): Boolean

This containsKey() function of Map returns true if the map contains the specified 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 check if map1 contains the key 2.
As 2 is present in the keys of map1, true is returned.
We print the result to standard output.

Kotlin Program

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

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 check if map2 contains the key 'd'.
As 'd' is not present in the keys of map2, false is returned.
We print the result to standard output.

Kotlin Program

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

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 check if map3 contains the key 'banana'.
As 'banana' is present in the keys of map3, true is returned.
We print the result to standard output.

Kotlin Program

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

Output

true

Summary

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