Kotlin List firstOrNull()
Syntax & Examples

Syntax of List.firstOrNull()

There are 2 variations for the syntax of List.firstOrNull() extension function. They are:

fun <T> List<T>.firstOrNull(): T?

This extension function returns the first element, or null if the list is empty.

fun <T> Iterable<T>.firstOrNull( predicate: (T) -> Boolean ): T?

This extension function returns the first element matching the given predicate, or null if element was not found.

✐ Examples

1 Example

In this example,

We create a list named list1 containing strings.
We use the firstOrNull function on list1 to get the first element or null if the list is empty.
The first element of 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.firstOrNull()
    println(result)
}

Output

apple

2 Example

In this example,

We create a list named list2 containing integers.
We use the firstOrNull function on list2 with a predicate that checks if an element is greater than 10.
Since there is no element of list2 that satisfies the predicate, null is returned and 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, 4, 5)
    val result = list2.firstOrNull { it > 10 }
    println(result)
}

Output

null

3 Example

In this example,

We create a list named list3 containing strings.
We use the firstOrNull function on list3 with a predicate that checks if a string's length is greater than 5.
The first element of list3 that satisfies the predicate 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", "world")
    val result = list3.firstOrNull { it.length > 5 }
    println(result)
}

Output

hello

Summary

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