java - java.lang.NumberFormatException:对于输入字符串:“firstno”

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我正在尝试运行一个程序。我真的是java的新手。当我运行程序时，出现以下异常。

type Exception report
message For input string: "firstno"

description The server encountered an internal error that prevented it from fulfilling his request.
exception

java.lang.NumberFormatException: For input string: "firstno"
java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
java.lang.Integer.parseInt(Integer.java:492)
java.lang.Integer.parseInt(Integer.java:527)
MathEx.doPost(MathEx.java:34)
javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

这是我的代码供您参考。

import java.sql.*;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class MathEx extends HttpServlet
{
public void doGet(HttpServletRequest p, HttpServletResponse q) throws ServletException, IOException
  {
    q.setContentType("Text/HTML");
    PrintWriter out = q.getWriter();

    out.println("<form method=post>");
    out.println("Enter first number");
    out.println("<input type=text name=first>");
    out.println("<br><br>");
    out.println("Enter second no.");
    out.println("<input type=text name=second>");
    out.println("<br><br>");
    out.println("<input type=submit name=send value=ADDITION>");
    out.println("<input type=submit name=send value=SUBSTRACTION>");

    out.println("<input type=submit name=send value=END>");
    out.println("</form>");
   }

 public void doPost(HttpServletRequest s, HttpServletResponse t) throws ServletException, IOException
     {
      t.setContentType("TEXT/HTML");
      PrintWriter out=t.getWriter();
      String firstno = s.getParameter("first");
      String secondno = s.getParameter("Second");
      String choice = s.getParameter("send");
      int fno=Integer.parseInt("firstno");
      int sno=Integer.parseInt("secondno");
      int result;
      out.println("First no ="+fno);
      out.println("<br><br>");
      out.println("Second no ="+sno);
      out.println("<br><br>");

 if (choice.equals("ADDITION"))
 {
  result=fno+sno;
  out.println("The result of addition= "+result);
 }


 if (choice.equals("SUBSTRACTION"))
 {
   result=fno-sno;
   out.println("The result of substraction= "+result);
 }


 if (choice.equals("END"))
 {
  out.println("Thank you have a nice day");
  return;
 }


  out.println("<br><br><br>");
  doGet(s,t);
 {
   out.println("<br><br><br>");
   out.println("bye  bye");
 }

}

}

我真的不明白为什么会这样。请给我任何参考或提示。

最佳答案

int fno=Integer.parseInt(firstno);
int sno=Integer.parseInt(secondno);

它应为变量firstno，但不能为字符串"firstno"。