Array Declaration in Kotlin

Introduction

Array Declaration 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.

Arrays store multiple values of the same type in a fixed-size container. 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

• Arrays store multiple values of the same type in a fixed-size container.
• Use arrayOf() for inferred type or Array for explicit declaration.
• Array indices start from zero.

Syntax

val numbers = arrayOf(1, 2, 3)

Array Declaration in Kotlin Example Program in Kotlin

fun main(args: Array<String>) {
    val numbers = arrayOf(10, 20, 30)
    println("First: ${numbers[0]}")
    println("Size: ${numbers.size}")
}

Sample Output

First: 10
Size: 3

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 numbers = arrayOf(10, 20, 30) assigns or updates a value used later in the program.

3. The println("First: ${numbers[0]}") statement writes a line to the console — this produces part of the sample output below.

4. The println("Size: ${numbers.size}") statement writes a line to the console — this produces part of the sample output below.

5. Arrays store multiple values of the same type in a fixed-size container.

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 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

• Arrays store multiple values of the same type in a fixed-size container.
• Use arrayOf() for inferred type or Array for explicit declaration.
• Array indices start from zero.
• 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.