Array Iteration in Kotlin

Introduction

Array Iteration 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.

For loops can iterate over arrays directly. 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

• for loops can iterate over arrays directly.
• indices property gives valid index range for arrays.
• forEach can also be used for simple iteration.

Syntax

for (item in array) { ... }

Array Iteration in Kotlin Example Program in Kotlin

fun main(args: Array<String>) {
    val languages = arrayOf("C", "Java", "Kotlin")
    for (lang in languages) {
        println(lang)
    }
}

Sample Output

C
Java
Kotlin

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 languages = arrayOf("C", "Java", "Kotlin") assigns or updates a value used later in the program.

3. The println(lang) statement writes a line to the console — this produces part of the sample output below.

4. For loops can iterate over arrays directly.

5. 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

• for loops can iterate over arrays directly.
• indices property gives valid index range for arrays.
• forEach can also be used for simple iteration.
• 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.