FileReader

// ── Pre-Java-11 constructors: implicit platform default charset ────────
// DANGEROUS on Windows where default may be Cp1252, not UTF-8:
FileReader legacy1 = new FileReader("file.txt");           // platform default
FileReader legacy2 = new FileReader(new File("file.txt")); // platform default
// Both read UTF-8 files incorrectly on Windows if platform default != UTF-8

// ── Java 11+: explicit charset constructors ────────────────────────────
import java.nio.charset.StandardCharsets;

FileReader utf8Reader = new FileReader("file.txt", StandardCharsets.UTF_8);
FileReader latin1Reader = new FileReader(new File("file.txt"), StandardCharsets.ISO_8859_1);
// Charset is explicit — no platform-dependency

// ── What platform default charset is on this JVM ─────────────────────
System.out.println(Charset.defaultCharset());  // e.g., "UTF-8" or "windows-1252"
// Add -Dfile.encoding=UTF-8 JVM arg to force UTF-8 when platform default is wrong

// ── Reading characters one at a time ─────────────────────────────────
try (FileReader fr = new FileReader("text.txt", StandardCharsets.UTF_8)) {
    int ch;
    while ((ch = fr.read()) != -1) {   // read() returns int: 0-65535 for char, -1 for EOF
        System.out.print((char) ch);   // cast int to char for use
    }
}

// ── Reading into a char array ─────────────────────────────────────────
try (FileReader fr = new FileReader("text.txt", StandardCharsets.UTF_8)) {
    char[] buffer = new char[1024];
    int charsRead;
    StringBuilder sb = new StringBuilder();
    while ((charsRead = fr.read(buffer, 0, buffer.length)) != -1) {
        sb.append(buffer, 0, charsRead);  // append only the chars actually read
    }
    System.out.println(sb.toString());
}

// ── The -1 return and end-of-file contract ────────────────────────────
try (FileReader fr = new FileReader("empty.txt", StandardCharsets.UTF_8)) {
    int ch = fr.read();
    System.out.println(ch);   // -1 immediately — file is empty
}

// ── Preferred alternative 1: Files.newBufferedReader ─────────────────
// Cleaner, always buffered, explicit charset, idiomatic modern Java:
try (BufferedReader br = Files.newBufferedReader(
        Path.of("text.txt"), StandardCharsets.UTF_8)) {
    String line;
    while ((line = br.readLine()) != null) {
        System.out.println(line);
    }
}

// ── Preferred alternative 2: InputStreamReader for flexibility ────────
// Allows wrapping any InputStream (network, classpath, etc.):
InputStream is = getClass().getResourceAsStream("/data/config.txt");
try (BufferedReader br = new BufferedReader(
        new InputStreamReader(is, StandardCharsets.UTF_8))) {
    String line;
    while ((line = br.readLine()) != null) {
        System.out.println(line);
    }
}

// ── The mandatory pattern: FileReader wrapped in BufferedReader ────────
try (BufferedReader br = new BufferedReader(
        new FileReader("document.txt", StandardCharsets.UTF_8))) {

    String line;
    int lineNumber = 0;
    while ((line = br.readLine()) != null) {
        lineNumber++;
        System.out.printf("%4d: %s%n", lineNumber, line);
    }
}

// ── readLine() return value contract ─────────────────────────────────
try (BufferedReader br = new BufferedReader(
        new FileReader("data.csv", StandardCharsets.UTF_8))) {

    String line = br.readLine();   // first line (no trailing 
 or 
)
    if (line == null) {
        System.out.println("File is empty");
    } else {
        System.out.println("First line: " + line);
        // line does NOT include the line terminator
    }
}

// ── Line terminators: readLine() handles all three ────────────────────
// 
   (Unix/Linux/macOS)
// 

 (Windows)
// 
   (old Classic Mac OS)
// readLine() handles all three transparently — no need to strip terminators

// ── Processing CSV with BufferedReader wrapping FileReader ─────────────
List<String[]> records = new ArrayList<>();
try (BufferedReader br = new BufferedReader(
        new FileReader("data.csv", StandardCharsets.UTF_8))) {
    String line;
    br.readLine();   // skip header line
    while ((line = br.readLine()) != null) {
        if (!line.isBlank()) {   // skip empty lines
            records.add(line.split(",", -1));  // split on comma, keep trailing empty fields
        }
    }
}

// ── Modern alternative: Files.newBufferedReader ───────────────────────
// Exactly equivalent to new BufferedReader(new FileReader(path, charset))
// but shorter and more idiomatic:
try (BufferedReader br = Files.newBufferedReader(
        Path.of("document.txt"), StandardCharsets.UTF_8)) {
    br.lines()                   // Stream<String> of lines
      .filter(line -> !line.isBlank())
      .map(String::trim)
      .forEach(System.out::println);
}

// ── Stream<String> via lines() — lazy line reading ────────────────────
try (BufferedReader br = Files.newBufferedReader(
        Path.of("large.log"), StandardCharsets.UTF_8)) {
    long errorCount = br.lines()
        .filter(line -> line.contains("ERROR"))
        .count();
    System.out.println("Errors: " + errorCount);
}   // BufferedReader closed when try-with-resources exits — stream also closed

// ── ready() for non-blocking check (rarely needed) ───────────────────
try (BufferedReader br = new BufferedReader(
        new FileReader("file.txt", StandardCharsets.UTF_8))) {
    if (br.ready()) {
        System.out.println("Data available: " + br.readLine());
    }
    // ready() on a file with BufferedReader: true if buffer has data or file has more
    // NOT equivalent to "has more lines" — don't use as loop condition
}