Path & Files — The NIO.2 API

import java.nio.file.*;
import java.nio.charset.StandardCharsets;
import java.io.IOException;
import java.util.List;

public class FilesAndPath {
    public static void main(String[] args) throws IOException {
        // Path — represents a file/directory location (OS-agnostic)
        Path home    = Path.of(System.getProperty("user.home"));  // Java 11+
        Path catalog = home.resolve("library").resolve("catalog.txt");  // appends
        Path reports = Path.of("reports", "2024", "Q1.txt");     // relative path

        // Path info
        System.out.println(catalog.getFileName());   // catalog.txt
        System.out.println(catalog.getParent());     // /home/user/library
        System.out.println(catalog.isAbsolute());    // depends on construction
        System.out.println(catalog.toAbsolutePath());

        // Check existence & properties
        Path file = Path.of("src/data/books.txt");
        System.out.println(Files.exists(file));
        System.out.println(Files.isRegularFile(file));
        System.out.println(Files.isDirectory(file.getParent()));
        System.out.println(Files.size(file));  // bytes

        // Create directories
        Files.createDirectories(Path.of("output/reports/2024"));  // creates all parents

        // Write to file (UTF-8, overwrites)
        List<String> lines = List.of("Clean Code,Robert Martin,39.99",
                                     "Effective Java,Joshua Bloch,44.99");
        Files.write(Path.of("catalog.csv"), lines, StandardCharsets.UTF_8);
        // For append mode: Files.write(path, lines, UTF_8, APPEND) — StandardOpenOption.APPEND

        // Read all lines at once (good for small files)
        List<String> readLines = Files.readAllLines(Path.of("catalog.csv"), StandardCharsets.UTF_8);
        readLines.forEach(System.out::println);

        // Read entire file as a string
        String content = Files.readString(Path.of("catalog.csv"));   // Java 11+

        // Copy & move
        Files.copy(Path.of("source.txt"), Path.of("backup.txt"),
                   StandardCopyOption.REPLACE_EXISTING);
        Files.move(Path.of("temp.txt"), Path.of("archive/temp.txt"),
                   StandardCopyOption.REPLACE_EXISTING);

        // Delete
        Files.deleteIfExists(Path.of("temp.txt"));  // no exception if not found

        // Walk directory tree
        try (var stream = Files.walk(Path.of("src"))) {
            stream.filter(Files::isRegularFile)
                  .filter(p -> p.toString().endsWith(".java"))
                  .forEach(System.out::println);
        }

        // List directory (one level)
        try (var entries = Files.list(Path.of("."))) {
            entries.sorted().forEach(System.out::println);
        }
    }
}