求大神解决！实在没想明白。计算完符号总是除。。。
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
double a=Double.parseDouble(request.getParameter("num1"));
double b=Double.parseDouble(request.getParameter("num2"));
double result=0;
String slected=null;
if(request.getParameter("compute").equals("+")){
result=a+b;
slected="1";
}
else if(request.getParameter("compute").equals("-")){
result=a-b;
slected="2";
}
else if(request.getParameter("compute").equals("*")){
result=a*b;
slected="3";
}
else{
result=a/b;
slected="4";
}
request.setAttribute("sel", slected);
request.setAttribute("cont", result);
request.getRequestDispatcher("index.jsp").forward(request, response);
}