<%@ page import="java.text.NumberFormat" %>
<%
String amountString = request.getParameter ( "amount" );

String discountRateString = request.getParameter ( "discountRate" );

String taxRateString = request.getParameter ( "taxRate" );

if ( amountString != null && ! amountString.matches ( "^[0-9]+$" ) )
{
	amountString = amountString.replaceAll ( "[^\\d.]", "" );
}
if ( discountRateString != null && ! discountRateString.matches ( "^[0-9]+$" ) )
{
	discountRateString = discountRateString.replaceAll ( "[^\\d.]", "" );
}
if ( taxRateString != null && ! taxRateString.matches ( "^[0-9]+$" ) ) 
{
	taxRateString = taxRateString.replaceAll ( "[^\\d.]", "" );
}

double amount = 0.0;
double discountRate = 0.0;
double taxRate = 0.0;

try
{

if ( amountString == null || amountString == "" )
{
   amountString = "";
}
else
{
   amount = Double.valueOf ( amountString ).doubleValue();
}

if ( discountRateString == null || discountRateString == "" )
{
   discountRateString = "";
}
else
{
   discountRate = Double.valueOf ( discountRateString ).doubleValue();
}

if ( taxRateString == null || taxRateString == "" )
{
   taxRateString = "";
}
else
{
   taxRate = Double.valueOf ( taxRateString ).doubleValue();
}

}
catch ( NumberFormatException ex )
{
	amountString = "";
	discountRateString = "";
	taxRateString = "";
%>

That was naughty. Please use numbers and fill in all fields.

<%
}
    double discount = amount * discountRate; 
    double total = amount - discount; 
    double tax = total * taxRate; 
    double taxedTotal = tax + total; 
    
    NumberFormat numberFormat = NumberFormat.getCurrencyInstance(); 

// let's print out what example this is
String submitString = request.getParameter ( "submit" );
%>


  
Enter Amount
  
  


  Enter Discount Rate
  
  


  Enter Tax Rate
  
  


  
  




Subtotal: <%= numberFormat.format(amount) %>
  

Discount: <%= numberFormat.format(discount) %> 
  

Total : <%= numberFormat.format(total)  %> 
  

Tax : <%= numberFormat.format(tax) %> 
  

Tax+Total: <%= numberFormat.format(taxedTotal) %>