NIO.2 Path and Files Classes

NIO.2 is the modern file API in Java, in the java.nio.file package, added in Java 7. It has two central types. Path is an interface that represents a location in the file system, such as school/2026/marks.txt; it doesn't open or touch the file. Files is a utility class of static methods that do the actual work: create, read, write, copy, move, delete and inspect files. In this lesson, you will learn how to build and work with paths, and the most important methods of Files.

Creating a Path

Paths.get(...) is an older equivalent of Path.of(...).

Methods of Path

Example: Working with Paths

Let's see an example of path operations. None of these files need to exist.

import java.nio.file.Path;
 
public class PathDemo {
    public static void main(String[] args) {
        Path marks = Path.of("school", "2026", "marks.txt");
 
        System.out.println("Path:      " + marks);
        System.out.println("File name: " + marks.getFileName());
        System.out.println("Parent:    " + marks.getParent());
        System.out.println("Parts:     " + marks.getNameCount());
        System.out.println("Absolute?  " + marks.isAbsolute());
 
        Path report = marks.resolveSibling("report.pdf");
        System.out.println("Sibling:   " + report);
 
        Path messy = Path.of("school/2026/../2025/./notes.txt");
        System.out.println("Normalized: " + messy.normalize());
 
        Path base = Path.of("school");
        System.out.println("Relative:  " + base.relativize(marks));
        System.out.println("Ends with marks.txt? "
            + marks.endsWith("marks.txt"));
    }
}

Path:      school/2026/marks.txt
File name: marks.txt
Parent:    school/2026
Parts:     3
Absolute?  false
Sibling:   school/2026/report.pdf
Normalized: school/2025/notes.txt
Relative:  2026/marks.txt
Ends with marks.txt? true

Explanation: Path.of joins the parts with the correct separator (/ on macOS and Linux, \ on Windows). resolveSibling swaps the file name. normalize removes .. (which cancels 2026) and .. relativize gives the path from school to the file.

Methods of Files

Example: Inspecting a File

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
 
public class Inspect {
    public static void main(String[] args) throws IOException {
        Path file = Path.of("diary.txt");
        Files.writeString(file, "Dear diary, today Advitha learned NIO.2.");
 
        System.out.println("Regular file? " + Files.isRegularFile(file));
        System.out.println("Directory?    " + Files.isDirectory(file));
        System.out.println("Readable?     " + Files.isReadable(file));
        System.out.println("Size:         " + Files.size(file) + " bytes");
        System.out.println("Exists other? "
            + Files.exists(Path.of("nope.txt")));
    }
}

Regular file? true
Directory?    false
Readable?     true
Size:         40 bytes
Exists other? false

Explanation: Files.writeString creates the file with the text. The is... methods check what kind of entry it is and what the program may do with it, and size returns its length in bytes.

Common Mistakes

Expecting Path.of("a.txt") to create a file. Use Files.createFile or a write method.

Forgetting normalize() before comparing paths. a/../b and b are different Path objects until normalized.

Using string concatenation for paths. Use resolve.

Interview Corner

Practice

1. Easy: Build the path reports/2026/november.csv and print its file name, parent and number of parts.
2. Harder: Write a method that changes a file's extension, such as marks.txt to marks.csv, using resolveSibling and string methods.

Key Takeaways