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Editorial Team
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Asked: 2026-06-01T21:19:21+00:00

I am writing a simple web app that performs calculations. I have 2 buttons,

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I am writing a simple web app that performs calculations. I have 2 buttons, for adding and subtracting, but they aren’t working. I tried to use a switch statement and an if statement, but neither are working. Could you please assist me to understand the problem.

Here is my code…

<%
String name = (String) session.getAttribute("name");
if (name==null) {
    name = request.getParameter("name");
    if (name!=null){
        session.setAttribute("name",name);
    }
}

String sum = (String) session.getAttribute("sum");
if (sum==null) {
    sum = "0";
    session.setAttribute("sum",sum);
}
int isum = Integer.parseInt(sum);

String number = request.getParameter("number");
if (number==null){
    number = "0";
}
int inumber = Integer.parseInt(number);
if(request.getParameter("add") != null){ 
    isum += inumber;
    session.setAttribute("sum",""+isum);
}
if(request.getParameter("subtract") != null){
    isum += inumber;
    session.setAttribute("sum",""+isum);
}
%>

<html>
    <head>
    <title>Adding Machine</title>
    </head>

    <body>
        <form method='get' action='adder.jsp'>
            <%
            if (name==null) {
            %>
                <p>
                    Name: <input type='text' name='name' id='name'>
                </p>
                <p>
                    <input type='submit' name='submit' id='submit' value='signin'>
                </p>
            <%
            } else {
            %>
                <p>Welcome, <%=name%>!</p>
                <p>Current sum is: <%=isum%></p>
                <p>
                    Number to add: <input type='text' name='number' id='number' value='add'>
                </p>
                <p>
                     <input type='submit' name='submit' id='submit' value='add'>
                </p>
                <p>
                    <input type='submit' name='submit' id='submit' value='subtract'>
                </p>
            <%
            }
            %>
        </form>
    </body>
</html>
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1 Answer

  1. Editorial Team

    It seems you have badly copied example from somewhere:

    Syntax of request.getParameter() is :

    request.getParameter("formParamName");

    Read More at : Java Docs

    Here you will definately get NULL as there is no parameter named “add” or “subtract”.

    Change your code to 

    if(request.getParameter("submit") != null){ 

    if(request.getParameter("submit").equals("add"))
        isum += inumber;
    else if(request.getParameter("submit").equals("subtract"))
        isum -= inumber;
    session.setAttribute("sum",""+isum);
}
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