输入流， 标记（）， 复位（）

方法和方法是如何准确工作的（在下面的代码中），一步一步？我试图编写自己的示例，但开始抛出错误的标记异常或类似情况，我无法理解在此代码中放置标记和重置方法的意义，因为我看不到与此或没有区别。mark()reset()

import java.io.*;

class BufferedInputStreamDemo {
    public static void main(String args[]) {
        String s = "© is a copyright symbol, "
                + "however &copy isn't.\n";
        byte buf[] = s.getBytes();

        ByteArrayInputStream in = new ByteArrayInputStream(buf);
        int c;
        boolean marked = false;

        //try_with_resources
        try (BufferedInputStream f = new BufferedInputStream(in)) {
            while ((c = f.read()) != -1) {
                switch (c) {
                    case '&':
                        if (!marked) {
                            f.mark(32);
                            marked = true;
                        } else {
                            marked = false;
                        }
                        break;
                    case ';':
                        if (marked) {
                            marked = false;
                            System.out.print("(c)");
                        } else
                            System.out.print((char) c);
                        break;
                    case ' ':
                        if (marked) {
                            marked = false;
                            f.reset();
                            System.out.print("&");
                        } else
                            System.out.print((char) c);
                        break;
                    default:
                        if (!marked)
                            System.out.print((char) c);
                        break;
                }
            }
        } catch (IOException e) {
            System.out.println("I/O Error: " + e);
        }
    }
}