Kotlin List.firstOrNull() – Examples

Kotlin List.firstOrNull()

The Kotlin List.firstOrNull() function is used to retrieve the first element of a list or the first element satisfying a given predicate. If the list is empty or no element satisfies the predicate, it returns null.

Syntax

List.firstOrNull()

Returns the first element, or null if the list is empty.

List.firstOrNull(predicate)

Returns the first element matching the given predicate, or null if element was not found.

The return type of firstOrNull() would be same as that of the returned element.

Example 1: Getting the first element of a list

In this example, we shall take an integer list, and get the first element of this list using List.firstOrNull(), without passing any predicate.

Program

fun main() {
    val numbers = listOf(10, 20, 30, 40, 50)
    val firstNumber = numbers.firstOrNull()
    println(firstNumber)
}

Output

10

Example 2: Getting the first element that satisfies a condition

In this example, we shall take a list of strings, and get the first string element that starts with the character 'b', using List.first() function with the predicate.

Program

fun main() {
    val fruits = listOf("apple", "banana", "cherry", "berry")
    val firstBFruit = fruits.firstOrNull{ it.startsWith('b') }
    println(firstBFruit)
}

Output

banana

Example 3: Using firstOrNull() with an empty list

In this example, we shall take an empty list of integers, and print the return value of firstOrNull() for this list.

Program

fun main() {
    val emptyList = listOf<Int>()
    val firstElement = emptyList.firstOrNull()
    println(firstElement)
}

Output

null