Accessing Array Elements in Kotlin

Introduction

Accessing Array Elements is a fundamental concept every Kotlin developer should understand. Arrays store a fixed number of elements in memory with fast index-based access. They are useful when size is known upfront or when interoping with Java APIs.

Elements are accessed using the index operator [ ]. 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

• Elements are accessed using the index operator [ ].
• Attempting to access an invalid index throws ArrayIndexOutOfBoundsException.
• Arrays also provide first(), last() and get/set methods.

Syntax

val value = array[index]

Accessing Array Elements in Kotlin Example Program in Kotlin

fun main(args: Array<String>) {
    val marks = arrayOf(85, 90, 78)
    println("Second mark: ${marks[1]}")
    marks[1] = 92
    println("Updated second mark: ${marks[1]}")
}

Sample Output

Second mark: 90
Updated second mark: 92

When to use

Use arrays when you need fixed-size storage, primitive arrays without boxing overhead, or compatibility with Java vararg APIs.

How it works

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

2. val marks = arrayOf(85, 90, 78) assigns or updates a value used later in the program.

3. The println("Second mark: ${marks[1]}") statement writes a line to the console — this produces part of the sample output below.

4. marks[1] = 92 assigns or updates a value used later in the program.

5. The println("Updated second mark: ${marks[1]}") statement writes a line to the console — this produces part of the sample output below.

6. Elements are accessed using the index operator [ ].

7. 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 listOf or arrayOf factory functions over manual size allocation when possible.
• Use typed arrays (IntArray) for numeric data to avoid boxing overhead.
• Bounds-check mentally: invalid indices throw IndexOutOfBoundsException.

Common Mistakes

• Confusing Array<Int> (boxed) with IntArray (unboxed primitives).
• Assuming arrays are dynamically resizable like ArrayList — they are fixed size.
• Using reference equality (===) when comparing array contents — use contentEquals.

Key Points

• Elements are accessed using the index operator [ ].
• Attempting to access an invalid index throws ArrayIndexOutOfBoundsException.
• Arrays also provide first(), last() and get/set methods.
• 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.