Kotlin String - indexOfLast() Function

The Kotlin string indexOfLast() function is used to return index of the last character matching the given predicate, or -1 if the char sequence does not contain such character.

This function provides a simple way to perform reverse conditional search operations for many use cases, including string validation, substring extraction, and data analysis.

Syntax

Following is the syntax of the Kotlin string indexOfLast() function −

fun CharSequence.indexOfLast(
   predicate: (Char) -> Boolean
): Int

Parameters

This function accepts a predicate representing the lambda function that defines the condition to match. It is applied to each character in the string until the condition is satisfied.

Return value

This function returns an index of the last character matching the predicate, or -1 if the string does not contain such a character.

Example 1: Get the Index of Last Char

Following is the basic example, we use indexOfLast() to get the index of the last char matching the predicate in kotlin −

fun main() {
   val str = "This is kotlin"
   val index = str.indexOfLast { it in "aeiou" }
   println("Index of the last vowel: $index")
}

Output

Following is the output −

Index of the last vowel: 12

Example 2: Get the Index of Last Digit

Now, let's look at another example of the indexOfLast() to get the index of the last digit in the string −

fun main() {
   val str = "Hello, sector136"
   val index = str.indexOfLast { it.isDigit() }
   println("Index of last Digit: $index")
}

Output

Following is the output −

Index of last Digit: 15

Example 3: Get the Index of the Last Uppercase

In this example, we display the index of the last uppercase letter using the indexOfLast() in Kotlin −

fun main() {
   val str = "hello TutorialsPoint"
   val index = str.indexOfLast { it.isUpperCase() }
   println("Index of last uppercase: $index")
}

Output

Following is the output −

Index of last uppercase: 15