Kotlin Array first()

Kotlin Array first()

In Kotlin, the Array first() function is used to obtain the first element of the array that satisfies the given predicate(condition). It returns the element if it finds the element, or throws a NoSuchElementException if the array is empty.

If no predicate is given, then first() function returns the first element in the array.

In this tutorial, we’ll explore the syntax of the first() function and provide examples of its usage in Kotlin arrays.

Syntax

The syntax of the first() function is as follows:

fun <T> Array<out T>.first(): T
fun <T> Array<out T>.first(predicate: (T) -> Boolean): T

where

Parameter	Description
predicate	A lambda function that takes the element of array as argument and returns true or false.

If no element satisfies the predicate or if the array is empty, the function throws a NoSuchElementException.

Examples for Array first() function

1. Using first() with an Array of Numbers

In this example, we’ll use first() to obtain the first element of an array of numbers numbersArray that satisfies the condition that the element is exactly divisible by 3.

Kotlin Program

fun main() {
    val numbersArray = arrayOf(10, 15, 20, 25, 30)

    // Using first() to obtain the first element that is exactly divisible by 3
    val firstElement = numbersArray.first{it % 3 == 0}

    println("First Element (exactly divisible by 3) : $firstElement")
}

Output

First Element (exactly divisible by 3) : 15

2. Using first() with no predicate

We have already learnt that if no predicate is given to first() function, then it returns the first element in the array.

Kotlin Program

fun main() {
    val numbersArray = arrayOf(10, 15, 20, 25, 30)

    // Using first() to obtain the first element
    val firstElement = numbersArray.first()

    println("First Element : $firstElement")
}

Output

First Element : 10

3. Using first() with an Empty Array

In this example, we’ll use first() with an empty array to demonstrate the NoSuchElementException when the array is empty.

Kotlin Program

fun main() {
    val numbersArray = intArrayOf()

    // Using first() to obtain the first element
    val firstElement = numbersArray.first()

    println("First Element : $firstElement")
}

Output

Exception in thread "main" java.util.NoSuchElementException: Array is empty.
	at kotlin.collections.ArraysKt___ArraysKt.first(_Arrays.kt:1045)
	at MainKt.main(Main.kt:5)
	at MainKt.main(Main.kt)

You may use a try-catch block to handle this exception.

Summary

In this tutorial, we’ve covered the first() function in Kotlin arrays, its syntax, and how to use it to obtain the first element of an array. Remember to handle the NoSuchElementException when using this function with an empty array to prevent runtime errors.