File Handling in Java

File handling in Java means working with files and folders on disk: creating them, writing data to them, reading data from them, and copying, moving, renaming and deleting them. Java has two APIs for this. The older java.io.File class has existed since Java 1.0. The modern NIO.2 API, added in Java 7 in the java.nio.file package, uses the Path interface and the Files class and is the recommended choice today. In this lesson, you will get an overview of both and a first complete example.

The Two APIs

Common File Operations at a Glance

Example: A Complete Round Trip

Let's see an example that creates a folder, writes a file, reads it, copies it and cleans up.

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.List;
 
public class RoundTrip {
    public static void main(String[] args) throws IOException {
        Path dir = Files.createDirectories(Path.of("school"));
        Path file = dir.resolve("students.txt");
 
        Files.write(file, List.of("Navika", "Srihitha", "Advitha"));
        System.out.println("Exists: " + Files.exists(file)
            + ", size: " + Files.size(file) + " bytes");
 
        List<String> names = Files.readAllLines(file);
        System.out.println("Read: " + names);
 
        Path backup = Files.copy(file, dir.resolve("students.bak"));
        System.out.println("Backup: " + backup);
 
        Files.delete(backup);
        Files.delete(file);
        Files.delete(dir);
        System.out.println("Cleaned up: " + Files.notExists(dir));
    }
}

Exists: true, size: 24 bytes
Read: [Navika, Srihitha, Advitha]
Backup: school/students.bak
Cleaned up: true

Explanation: Path.of("school") describes a location; Files.createDirectories creates the folder. resolve builds a path inside it. Files.write writes each name on its own line (6 + 8 + 7 letters plus 3 line breaks = 24 bytes), and readAllLines reads them back. Every operation is a single static call on Files.

Common Mistakes

Mixing up a path and a file. A Path is just a name; the file may or may not exist.

Ignoring IOException. File operations can fail for many reasons: missing files, permissions, full disks.

Hard-coding \ or / in paths. Use Path.of("a", "b") or resolve, which use the right separator.

Interview Corner

Practice

1. Easy: Create a folder notes, write a file with three lines into it, and print the number of lines.
2. Harder: Write a program that creates backup/2026-11-12/ (using today's date) and copies a file into it.

Key Takeaways