[]为什么HttpServlet中的方法基本都是protected

protected  void doDelete(HttpServletRequest req, HttpServletResponse resp)           protected  void doGet(HttpServletRequest req, HttpServletResponse resp)       protected  void doHead(HttpServletRequest req, HttpServletResponse resp)           protected  void doOptions(HttpServletRequest req, HttpServletResponse resp)           protected  void doPost(HttpServletRequest req, HttpServletResponse resp)           protected  void doPut(HttpServletRequest req, HttpServletResponse resp)            protected  void doTrace(HttpServletRequest req, HttpServletResponse resp)           protected  long getLastModified(HttpServletRequest req) protected  void service(HttpServletRequest req, HttpServletResponse resp)