File Reading and Writing Basics

In this lesson you will learn the basics of reading and writing files in Kotlin, so a program can save and load text files. This is for anyone searching for "Kotlin File read write how to use".

File.writeText() writes to a file and File.readText() reads one back. Saving configuration files and logs makes this a basic operation you will use often.

The sample code saves the contents of a note with File("memo.txt").writeText(...), then reads the same file back with File("memo.txt").readText(). It shows how neatly Kotlin's extension functions wrap Java's file API.

A common stumbling block for beginners is error handling for a missing file or a lack of write permission. Real code is expected to allow for failure with a try/catch.

In real-world development, file operations - saving configuration, writing to a log file - are needed by almost every application.

📖 Reference code

import java.io.File

fun main() {
    File("memo.txt").writeText("Hello\nThis is line 2")
    val content = File("memo.txt").readText()
    println(content)
}

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run Kotlin directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).