Read Text File in Kotlin

Introduction

Read Text File is a fundamental concept every Kotlin developer should understand. File I/O reads and writes persistent data on disk. Kotlin wraps Java file APIs with extension functions for cleaner syntax.

ReadText reads entire file content as String. 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

• readText reads entire file content as String.
• Available in kotlin.io for JVM and multiplatform projects.
• Use for small text files.

Syntax

val content = File("data.txt").readText()

Read Text File in Kotlin Example Program in Kotlin

import java.io.File

fun main(args: Array<String>) {
    val file = File.createTempFile("demo", ".txt")
    file.writeText("Hello Kotlin File")
    println(file.readText())
    file.deleteOnExit()
}

Sample Output

Hello Kotlin File

When to use

Use file I/O for reading config files, writing logs, or processing CSV/JSON stored on disk.

How it works

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

2. val file = File.createTempFile("demo", ".txt") assigns or updates a value used later in the program.

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

4. ReadText reads entire file content as String.

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

• Understand the core idea: readText reads entire file content as String.
• Prefer readable names and small functions so examples map directly to real projects.
• Run and modify the example — change values and observe how the output changes.

Common Mistakes

• Skipping the example and only reading the definition — hands-on practice cements the concept.
• Copying syntax without understanding nullable vs non-nullable types or scope rules.
• Ignoring compiler warnings that often point to safer alternatives.

Key Points

• readText reads entire file content as String.
• Available in kotlin.io for JVM and multiplatform projects.
• Use for small text files.
• Test the example locally and verify the output matches the sample.
• Experiment by changing input values to see how behaviour changes.

Notes

• File examples assume a writable working directory; adjust paths for your environment.
• Semicolons at the end of statements are optional in Kotlin.