How to Iterate Over List in Kotlin: Simple Examples

In Kotlin, you can iterate over a list using a for loop or the forEach function. Use for (item in list) to access each element, or list.forEach { item -> } for a lambda-based approach.

Syntax

To loop through a list in Kotlin, use the for loop or the forEach function.

• for loop: for (item in list) { /* code */ } runs code for each item.
• forEach function: list.forEach { item -> /* code */ } uses a lambda to process each item.

kotlin

val list = listOf("apple", "banana", "cherry")

// Using for loop
for (item in list) {
    println(item)
}

// Using forEach function
list.forEach { item ->
    println(item)
}

Example

This example shows how to print each fruit in a list using both for loop and forEach function.

kotlin

fun main() {
    val fruits = listOf("apple", "banana", "cherry")

    println("Using for loop:")
    for (fruit in fruits) {
        println(fruit)
    }

    println("Using forEach function:")
    fruits.forEach { fruit ->
        println(fruit)
    }
}

Output

Using for loop:
apple
banana
cherry
Using forEach function:
apple
banana
cherry

Common Pitfalls

Common mistakes when iterating over lists in Kotlin include:

• Using an index-based loop incorrectly, which can cause errors if the index is out of bounds.
• Modifying the list while iterating, which can cause runtime exceptions.
• Forgetting to use in keyword in the for loop.

Always prefer for (item in list) or forEach for safe and clear iteration.

kotlin

val list = listOf("a", "b", "c")

// Wrong: missing 'in' keyword
// for (item list) {
//     println(item)
// }

// Correct:
for (item in list) {
    println(item)
}

Quick Reference

Method	Syntax	Description
For loop	for (item in list) { /* code */ }	Simple and readable loop over each element.
forEach function	list.forEach { item -> /* code */ }	Lambda-based iteration, useful for inline actions.
Indexed loop	for (index in list.indices) { val item = list[index] }	Access elements with index, use carefully.
While loop	var i = 0; while (i < list.size) { val item = list[i]; i++ }	Less common, manual index control.

Key Takeaways

Use 'for (item in list)' for simple and clear iteration over lists.

The 'forEach' function offers a concise lambda-based way to loop through lists.

Avoid modifying a list while iterating to prevent errors.

Remember to include the 'in' keyword in 'for' loops to avoid syntax errors.

Use indexed loops only when you need the position of elements.