Is listOf truly immutable?

listOf returns a read-only view. The underlying list cannot be modified through the List reference. However, if you have a reference to the backing MutableList, you can modify it. For guaranteed immutability, use the immutable collections from kotlinx-collections-immutable.

How do I get the first or last element safely?

Use list.firstOrNull() and list.lastOrNull() instead of first() and last(), which throw if the list is empty.

Beginner 8 min readKotlin 2.0

Kotlin List — listOf and mutableListOf with Examples

A List is an ordered collection of elements. Kotlin has immutable (listOf) and mutable (mutableListOf) variants.

What You Will Learn

Create read-only lists with listOf
Create mutable lists with mutableListOf
Access elements by index
Add and remove elements
Iterate and filter lists

Read-Only List with listOf

listOf creates a list that cannot be modified — no add or remove.

listOf

kotlin
fun main() {
    val fruits = listOf("Apple", "Banana", "Cherry")
    println(fruits)
    println(fruits[0])
    println(fruits.size)
    println(fruits.contains("Banana"))
}

Output

[Apple, Banana, Cherry] Apple 3 true

fruits[0] accesses the first element. .size gives the element count. .contains() checks membership.

Beginner Tip: Use listOf for data that should not change — it communicates your intent clearly.

Mutable List with mutableListOf

mutableListOf allows adding, removing, and modifying elements.

mutableListOf

kotlin
fun main() {
    val nums = mutableListOf(1, 2, 3)
    nums.add(4)
    nums.add(0, 0)     // insert at index 0
    nums.remove(2)     // remove value 2
    nums.removeAt(0)   // remove at index 0
    println(nums)
}

Output

[1, 3, 4]

.add() appends an element or inserts at an index. .remove() removes by value. .removeAt() removes by index.

List Operations

Kotlin lists have powerful functional operations.

filter, map, sorted

kotlin
fun main() {
    val numbers = listOf(5, 1, 8, 3, 9, 2)
    println(numbers.filter { it > 4 })
    println(numbers.map { it * 2 })
    println(numbers.sorted())
    println(numbers.sum())
    println(numbers.max())
}

Output

[5, 8, 9] [10, 2, 16, 6, 18, 4] [1, 2, 3, 5, 8, 9] 28 9

filter returns elements matching a predicate. map transforms each element. sorted returns a new sorted list. sum and max are convenience functions.

Common List Functions

Key List API at a glance.

first, last, find, indexOf

kotlin
fun main() {
    val items = listOf(10, 20, 30, 40, 50)
    println(items.first())
    println(items.last())
    println(items.find { it > 25 })
    println(items.indexOf(30))
    println(items.isEmpty())
}

Output

10 50 30 2 false

.first() and .last() return the first/last element. .find() returns the first element matching the predicate, or null. .indexOf() returns the position of the element (-1 if not found).

Practice Exercise

Exercisepredict output

What prints? val list = mutableListOf(1,2,3) list.add(4) list.remove(2) println(list)

Quick Quiz

What is the difference between listOf and mutableListOf?

Kotlin List — listOf and mutableListOf with Examples

What You Will Learn

Read-Only List with listOf

listOf

Mutable List with mutableListOf

mutableListOf

List Operations

filter, map, sorted

Common List Functions

first, last, find, indexOf

Practice Exercise

Quick Quiz

Frequently Asked Questions

Related Tutorials