String to Integer Converting gives wrong output

Question

In my program i'm posting the payment amount value to controller and i'm converting that value to Integer. Because I need to convert this value to cents before calling web service. I'm using java and convert String to Integer code given below

(int)(Double.parseDouble(httpRequest.getParameter(PAYMENT_AMOUNT).trim()) * 100);

payment.jsp

page look like this

Payment Amount: <input type="text" id="paymentAmount" name="paymentAmount" value="1.00" />

For many input values it gives the correct output.

But for some values like 8.03 as input it return 802 as output value . This happens in 9.03,9.04 ,10.03,10.04,11.03 etc ... what could be the reason for this issue?

Peter Lawrey · Accepted Answer · 2016-02-04 22:49:15Z

2

You need to round the result. The problem you have is that floating point numbers are almost but not exactly the number it appears when printed as a string. This shows up as a problem when you perform calculations.

I suggest you try

(int) Math.round( Double.parseDouble( httpRequest.getParameter(PAYMENT_AMOUNT).trim()) * 100);

In your specific case, you can see with BigDecimal what the actual representation of a double is

double d = 8.03;
BigDecimal bd = new BigDecimal(d);
System.out.println("bd: " + bd);
double d100 = d * 100;
System.out.println("d100: " + d100);
int i100 = (int) d100;
System.out.println("i100: " + i100);
int r100 = (int) Math.round(d100);
System.out.println("r100: " + r100);

prints

bd: 8.0299999999999993605115378159098327159881591796875
d100: 802.9999999999999
i100: 802
r100: 803

So you can see the actual value of 8.03 is slightly less than 8.03 which means however that when you * 100 and round down it means that you get 802 not 803 as expected.

The best solution is to round the result which finds the closest representable value.

edited Feb 4, 2016 at 22:49

answered Feb 4, 2016 at 22:44

Peter Lawrey

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1 Comment

prabath Over a year ago

Thanks . its working . and thanks for the explanation

jrm · Accepted Answer · 2016-02-04 23:23:07Z

As a side note, you might want to reconsider using int types to store cent values esp when dealing with large numbers.

To add more to earlier answers on floating-point issues in Java, and the need for BigDecimal, refer to some explanation here:

http://www.drdobbs.com/jvm/javas-floating-point-imprecision/240168744

You can change your code to:

(new BigDecimal(httpRequest.getParameter(PAYMENT_AMOUNT).trim(), MathContext.DECIMAL64)).multiply(new BigDecimal(100, MathContext.DECIMAL64)).intValue()

Another note: I would be cautious about assuming that you will get a String object back in the getParameter() call above esp. if someone is attempting to call your service without passing the PAYMENT_AMOUNT parameter.

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