Why my function is displaying a weird result when converting string to double?

Question

I have a very weird result when I'm using my function and I think that I'm missing something with the rounding and double in java.

For example, when I provide the value 00159,300 for number and 100 for conversion I have 15930,000000000002 which is not possible!

public static String convertMultiply(String number, String conversion) {
    number=number.replace(",", ".");
    BigDecimal res=BigDecimal.valueOf(Double.valueOf(number)*Integer.valueOf(conversion));
    res=res.stripTrailingZeros();
    return res.toPlainString().replace(".", ",");
}

thanks in advance!

Yeah but I will lose some precision if I do that, I'm a bit new in programming and I'm afraid of side effects — soufiane, Dec 20 '21 at 21:03
For speed, use floating point. For accuracy, use `BigDecimal`. Or multiply by a power of ten sufficient to eliminate your decimal fraction. — Basil Bourque, Dec 20 '21 at 23:17

score 5 · Accepted Answer · answered Dec 20 '21 at 21:03

5

Double is an approximation of decimal values in Java. Instead, replace your line using double with:

BigDecimal res = (new BigDecimal(number)).multiply(new BigDecimal(conversion));

answered Dec 20 '21 at 21:03

Kevin Hooke

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Why my function is displaying a weird result when converting string to double?

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