Java 中错误 : Null
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet("/ExampleMath")ExampleMath
public class ExampleMath extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doPost(HttpServletRequest HTTP_Request, HttpServletResponse HTTP_Response)
throws ServletException, IOException,NumberFormatException {
HTTP_Response.setContentType("text/html");
PrintWriter Print_Writer = HTTP_Response.getWriter();
int Number1 = Integer.parseInt(HTTP_Request.getParameter("first"));
int Number2 = Integer.parseInt(HTTP_Request.getParameter("second"));
String Symbol = HTTP_Request.getParameter("math");
int result = 0;
if(Symbol.equals("addition"))
result = Number1 + Number2;
else if(Symbol.equals("substraction"))
result = Number1 - Number2;
else if(Symbol.equals("multiplication"))
result = Number1 * Number2;
else
result = Number1 / Number2;
Print_Writer.println(result);
}
}