Kotlin Tutorials

Kotlin Map firstNotNullOf()
Syntax & Examples

Syntax of Map.firstNotNullOf()

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

fun <K, V, R : Any> Map<out K, V>.firstNotNullOf( transform: (Entry<K, V>) -> R? ): R

This firstNotNullOf() extension function of Map returns the first non-null value produced by transform function being applied to entries of this map in iteration order, or throws NoSuchElementException if no non-null value was produced.


✐ Examples

1 Get first non-null character value in the map

In this example,

  • We create a map named map1 containing key-value pairs (1, 'a'), (2, null), (3, 'c').
  • We then apply the firstNotNullOf() function on map1, using the transform function { it.value } to extract values.
  • As a result, the first non-null value in map1 is returned.
  • We print the result to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val map1 = mapOf(1 to 'a', 2 to null, 3 to 'c');
    val result = map1.firstNotNullOf { it.value }
    print(result);
}

Output

a

2 Get first non-null integer value in the map

In this example,

  • We create a map named map2 containing key-value pairs ('a', 1), ('b', null), ('c', 3).
  • We then apply the firstNotNullOf() function on map2, using the transform function { it.value } to extract values.
  • As a result, the first non-null value in map2 is returned.
  • We print the result to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val map2 = mapOf('a' to 1, 'b' to null, 'c' to 3);
    val result = map2.firstNotNullOf { it.value }
    print(result);
}

Output

1

3 Get first non-null string value in the map

In this example,

  • We create a map named map3 containing key-value pairs (1, 'apple'), (2, null), (3, 'cherry').
  • We then apply the firstNotNullOf() function on map3, using the transform function { it.value } to extract values.
  • As a result, the first non-null value in map3 is returned.
  • We print the result to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val map3 = mapOf(1 to "apple", 2 to null, 3 to "cherry");
    val result = map3.firstNotNullOf { it.value }
    print(result);
}

Output

apple

Summary

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