为什么private不能修饰userService？求解

Question

private UserServiceImpl userService = new UserServiceImpl();报错，说private不允许写在这

public class RegistServlet extends HttpServlet {
    

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        private UserServiceImpl userService = new UserServiceImpl();

        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String email = req.getParameter("email");
        String code = req.getParameter("code");

        if (code.equalsIgnoreCase("abcde")){
            if (!userService.existsUsername(username)){//用户名不存在，注册成功
                userService.registUser(new User(null,username,password,email));
                req.getRequestDispatcher("/regist_success.html").forward(req,resp);
            }else {
                //用户名存在
                req.getRequestDispatcher("/regist.html").forward(req,resp);
            }

        }else {
            req.getRequestDispatcher("/regist.html").forward(req,resp);
        }
    }
}

Answer 1

一般把 private UserServiceImpl userService = new UserServiceImpl(); 这样的代码放在方法外面，作为全局变量使用。