List Basics in Kotlin

Introduction

List Basics is a fundamental concept every Kotlin developer should understand. Collections let you store and transform groups of values. Kotlin separates read-only and mutable views so you can express intent clearly in your APIs.

List is an ordered collection of elements. In this tutorial you will learn the syntax, walk through a complete example program, study the sample output, and review best practices so you can apply the concept confidently in your own projects.

Definition

• List is an ordered collection of elements.
• listOf() creates an immutable list.
• Lists allow duplicate values and maintain insertion order.

Syntax

val list = listOf("A", "B", "C")

List Basics in Kotlin Example Program in Kotlin

fun main(args: Array<String>) {
    val fruits = listOf("Apple", "Banana", "Cherry")
    println("First fruit: ${fruits.first()}")
    println("Contains Banana: ${fruits.contains("Banana")}")
}

Sample Output

First fruit: Apple
Contains Banana: true

When to use

Use collections when the number of items is dynamic or when you need map/set semantics instead of a plain list.

How it works

1. The program starts with a main function — the entry point that runs when you execute the file.

2. val fruits = listOf("Apple", "Banana", "Cherry") assigns or updates a value used later in the program.

3. The println("First fruit: ${fruits.first()}") statement writes a line to the console — this produces part of the sample output below.

4. The println("Contains Banana: ${fruits.contains("Banana")}") statement writes a line to the console — this produces part of the sample output below.

5. List is an ordered collection of elements.

6. Run the program in IntelliJ IDEA, Android Studio, or with the Kotlin command-line compiler (kotlinc / kotlin). Compare your console output with the sample output shown below.

Best Practices

• Prefer immutable listOf, setOf, mapOf for data that should not change after creation.
• Use map, filter, and fold instead of manual loops when transforming collections.
• Pick the smallest collection type that fits — don’t use a List when a Set is semantically correct.

Common Mistakes

• Modifying a list while iterating it — use filter or iterator remove carefully.
• Using mutableListOf when an immutable list would suffice, exposing accidental mutation.
• Calling get on a Map without checking key existence — prefer getOrDefault or getValue.

Key Points

• List is an ordered collection of elements.
• listOf() creates an immutable list.
• Lists allow duplicate values and maintain insertion order.
• Test the example locally and verify the output matches the sample.
• Experiment by changing input values to see how behaviour changes.

Notes

• Semicolons at the end of statements are optional in Kotlin.