Kotlin List indexOf()
Syntax & Examples

Syntax of List.indexOf()

The syntax of List.indexOf() function is:

abstract fun indexOf(element: E): Int

This indexOf() function of List returns the index of the first occurrence of the specified element in the list, or -1 if the specified element is not contained in the list.

✐ Examples

1 Example

In this example,

We create a list named list1 containing the elements 'a', 'b', 'c', 'd'.
We find the index of the first occurrence of 'a' using the List indexOf() function, which returns the index of the specified element.
The first occurrence of 'a' is at index 0 in list1, so indexA will be 0.
Finally, we print the value of indexA to standard output using the println function.

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf("a", "b", "c", "d")
    val indexA = list1.indexOf("a")
    println(indexA)
}

Output

2 Example

In this example,

We create a list named list1 containing the elements 10, 20, 30, 40.
We find the index of the first occurrence of 30 using the List indexOf() function, which returns the index of the specified element.
The first occurrence of 30 is at index 2 in list1, so index30 will be 2.
Finally, we print the value of index30 to standard output using the println function.

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf(10, 20, 30, 40)
    val index30 = list1.indexOf(30)
    println(index30)
}

Output

3 Example

In this example,

We create a list named list1 containing the elements 'apple', 'banana', 'cherry', 'date'.
We try to find the index of the first occurrence of 'grape' using the List indexOf() function, which returns the index of the specified element.
Since 'grape' is not present in list1, indexOf() returns -1.
Finally, we print the value of indexGrape to standard output using the println function.

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf("apple", "banana", "cherry", "date")
    val indexGrape = list1.indexOf("grape")
    println(indexGrape)
}

Output

-1

Summary

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