Kotlin List firstNotNullOfOrNull()
Syntax & Examples

Syntax of List.firstNotNullOfOrNull()

The syntax of List.firstNotNullOfOrNull() extension function is:

fun <T, R : Any> Iterable<T>.firstNotNullOfOrNull( transform: (T) -> R? ): R?

This firstNotNullOfOrNull() extension function of List returns the first non-null value produced by transform function being applied to elements of this collection in iteration order, or null if no non-null value was produced.


✐ Examples

1 Example

In this example,

  • We create a list named list1 containing strings.
  • We use the firstNotNullOfOrNull function on list1 with a transform function that returns the string if its length is greater than 5, otherwise null.
  • The first non-null value produced by the transform function on list1 is stored in result.
  • Finally, we print the value of result to standard output using the println statement.

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf("apple", "banana", "cherry")
    val result = list1.firstNotNullOfOrNull { if (it.length > 5) it else null }
    println(result)
}

Output

banana

2 Example

In this example,

  • We create a list named list2 containing integers and a null value.
  • We use the firstNotNullOfOrNull function on list2 with a transform function that returns the element itself.
  • The first non-null value produced by the transform function on list2 is stored in result.
  • Finally, we print the value of result to standard output using the println statement.

Kotlin Program

fun main(args: Array<String>) {
    val list2 = listOf(1, 2, 3, null, 5)
    val result = list2.firstNotNullOfOrNull { it }
    println(result)
}

Output

1

3 Example

In this example,

  • We create a list named list3 containing strings and a null value.
  • We use the firstNotNullOfOrNull function on list3 with a transform function that converts each string to uppercase, handling null values safely.
  • The first non-null value produced by the transform function on list3 is stored in result.
  • Finally, we print the value of result to standard output using the println statement.

Kotlin Program

fun main(args: Array<String>) {
    val list3 = listOf("hello", null, "world")
    val result = list3.firstNotNullOfOrNull { it?.toUpperCase() }
    println(result)
}

Output

HELLO

Summary

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