Why does JSP/JSTL division by 1000 sometimes give

问题:

When dividing by 1000 I sometime run across a bug that doesn't do the division "correctly". For example, when dividing 90.55 by 1000 instead of getting .09055 I get .090549999999.

<c:out value="${bean.paPrice / 1000}" />

Why is this happening? Is this a result of floating point math? A google search seemed to indicate that this may be a culprit, but I have found no concrete answer.

To fix this I can round the answer to 5 digits, but it seems like this is just a patch to a deeper problem.

<fmt:formatNumber type="number" maxFractionDigits="5" value="${bean.paPrice / 1000}" />

回答1:

It's not a problem, it's just a natural result of the binary representation of floating point. Round your values and don't worry about it.

回答2:

Why do computers suck at math?

http://www.codinghorror.com/blog/archives/001266.html

回答3:

Yes, this is a common floating-point format issue.