Kotlin List firstNotNullOf()
Syntax & Examples

Syntax of List.firstNotNullOf()

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

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

This firstNotNullOf() 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 throws NoSuchElementException if no non-null value was produced.

✐ Examples

1 Example

In this example,

We create a list named list containing strings.
We use the firstNotNullOf extension function on list to find the first element whose length is greater than 5.
The result is printed to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf("apple", "banana", "orange", "kiwi", "mango");
    val result = list.firstNotNullOf { if (it.length > 5) it else null };
    println(result);
}

Output

banana

2 Example

In this example,

We create a list named list containing integers.
We use the firstNotNullOf extension function on list to find the first element greater than 25.
The result is printed to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf(10, 20, 30, 40, 50);
    val result = list.firstNotNullOf { if (it > 25) it else null };
    println(result);
}

Output

3 Example

In this example,

We create a list named list containing characters.
We use the firstNotNullOf extension function on list to find the first element equal to 'c'.
The result is printed to standard output.

Kotlin Program

fun main(args: Array<String>) {
    val list = listOf('a', 'b', 'c', 'd', 'e');
    val result = list.firstNotNullOf { if (it == 'c') it else null };
    println(result);
}

Output

Summary

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