Reading & writing text with try-with-resources

Try-with-resources — the only safe pattern

A stream holds an OS file descriptor. If you forget to close it, the resource leaks — and eventually the JVM or OS will run out of file handles. Try-with-resources (TWR) guarantees close() is called even if an exception is thrown:

try (BufferedReader br = new BufferedReader(new FileReader("notes.txt"))) {
    String line;
    while ((line = br.readLine()) != null) {
        System.out.println(line);
    }
} // br.close() called automatically here — even if readLine() threw

readLine() returns null at end of file — that is the loop-termination condition, not an exception.

Writing with PrintWriter:

try (PrintWriter pw = new PrintWriter(new BufferedWriter(
        new FileWriter("output.txt", StandardCharsets.UTF_8)))) {
    pw.println("First line");
    pw.printf("Count: %d%n", 42);
}

Multiple resources in one TWR are closed in reverse declaration order:

try (InputStream in  = new FileInputStream("a.bin");
     OutputStream out = new FileOutputStream("b.bin")) {
    // closed: out first, then in
}

The resource variable must implement AutoCloseable. If both the body and close() throw, the close exception is suppressed (added to the primary exception via addSuppressed).