Kotlin List indexOfLast()
Syntax & Examples

Syntax of List.indexOfLast()

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

fun <T> List<T>.indexOfLast(predicate: (T) -> Boolean): Int

This extension function returns index of the last element matching the given predicate, or -1 if the list does not contain such element.

fun <T> Iterable<T>.indexOfLast( predicate: (T) -> Boolean ): Int

This extension function returns index of the last element matching the given predicate, or -1 if the collection does not contain such element.

✐ Examples

1 Example

In this example,

We create a list of strings named list1 containing elements "apple", "banana", "cherry".
We use the indexOfLast() function on list1 with a predicate to find the index of the last element starting with 'b'.
Since the last element starting with 'b' is "banana" at index 1 in list1, the result is 1.
Finally, we print the index to standard output using println statement.

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf("apple", "banana", "cherry")
    val index = list1.indexOfLast { it.startsWith("b") }
    println(index)
}

Output

2 Example

In this example,

We create a list of integers named list2 containing elements 10, 20, 30, 20, 40, 50.
We use the indexOfLast() function on list2 with a predicate to find the index of the last element equal to 20.
Since the last element equal to 20 is at index 3 in list2, the result is 3.
Finally, we print the index to standard output using println statement.

Kotlin Program

fun main(args: Array<String>) {
    val list2 = listOf(10, 20, 30, 20, 40, 50)
    val index = list2.indexOfLast { it == 20 }
    println(index)
}

Output

3 Example

In this example,

We create a list of strings named list3 containing elements "red", "blue", "green", "yellow".
We use the indexOfLast() function on list3 with a predicate to find the index of the last element with a length greater than 10.
Since there is no element in list3 with a length greater than 10, the result is -1.
Finally, we print the index to standard output using println statement.

Kotlin Program

fun main(args: Array<String>) {
    val list3 = listOf("red", "blue", "green", "yellow")
    val index = list3.indexOfLast { it.length > 10 }
    println(index)
}

Output

-1

Summary

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