Java File I/O

import java.nio.file.*;
import java.util.List;

Path path = Path.of("data.txt");

String content = Files.readString(path);            // whole file
List<String> lines = Files.readAllLines(path);      // list of lines

// large files — stream lines lazily
try (var stream = Files.lines(path)) {
    stream.filter(l -> !l.isBlank())
          .forEach(System.out::println);
}

Files.writeString(path, "Hello\n");
Files.writeString(path, "More\n", StandardOpenOption.APPEND);
Files.write(path, List.of("line 1", "line 2"));

Files.exists(path);
Files.isReadable(path);
Files.size(path);            // bytes
Files.createDirectories(Path.of("uploads/2026"));
Files.copy(source, target, StandardCopyOption.REPLACE_EXISTING);
Files.move(source, target);
Files.deleteIfExists(path);

Path p = Path.of("uploads", "2026", "photo.jpg");   // correct
Path abs = p.toAbsolutePath();
System.out.println(p.getFileName());   // photo.jpg
System.out.println(p.getParent());     // uploads/2026

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

try (var lines = Files.lines(Path.of("students.csv"))) {
    lines.skip(1)                        // header
         .map(line -> line.split(","))
         .forEach(cols -> System.out.println(cols[0] + " — " + cols[1]));
}