Не могу понять

public static void main(String[] args) throws IOException {
    BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
    String fileName = reader.readLine();
    reader.close();
    PrintStream original = System.out;
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    PrintStream stream = new PrintStream(outputStream);
    System.setOut(stream);
    testString.printSomething();
    System.setOut(original);
    FileOutputStream writer = new FileOutputStream(fileName);
    writer.write(outputStream.toByteArray());
    System.out.println(outputStream);
    writer.close();
    outputStream.close();
    stream.close();
}