File Reading and Writing Basics

This lesson covers the basics of reading and writing files in Java, so a program can save and load a text file. It's for anyone searching "Java Files.writeString usage."

Files.writeString() writes to a file, and Files.readString() reads one. A basic operation used constantly in real work — saving a config file or a log, for example.

The example saves memo content to a file with Files.writeString(Paths.get("memo.txt"), ...), then reads the same file and displays its content with Files.readString(...). This is a relatively concise file-handling API added in Java 11 and later.

A common early mistake is not accounting for the possibility that file operations can throw an exception. You need to declare throws Exception or wrap it in try-catch — forgetting either produces a compile error.

In real projects, using the asynchronous version of the API lets you handle reading and writing large files more efficiently.

📖 Reference code

import java.nio.file.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Files.writeString(Paths.get("memo.txt"), "Hello\nThis is line 2");
        String content = Files.readString(Paths.get("memo.txt"));
        System.out.println(content);
    }
}

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run Java 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).