编写了一个 servlet，为什么不能识别 request 和 response

package user.yourservle;
import *;
import javax.servlet.*;
import javax.servlet.http.*;

import org.omg.CORBA.Request;

import user.yourbean.SaveNumber;
public class HandleAverage extends HttpServlet{
    public void doGet(HttpServletRequest request,HttpServletResponse response)
    throws IOException,ServletException{}
    SaveNumber sn=new SaveNumber();
    String a=request.getParameter("a");
    String b=request.getParameter("b");
    try{
        int a1=Integer.parseInt(a);
        int b1=Integer.parseInt(b);
        double r;
        r=(a1+b1)/2.0;
        sn.setA(a1);
        sn.setB(b1);
        sn.setR(r);
        request.setAttribute("average",sn);
        RequestDispatcher rd=request.getRequestDispatcher("show.jsp");
        rd.forward(request, response);
    }catch(Exception e){}
   
}
}