在java中错误的十进制从Double转换为String

Question

I have A String that is formatted correctly to be cast to a double and it works fine for most decimals. The issue is that for .33, .67, and possibly others I haven't tested, the decimal becomes something like .6700000000002 , or .329999999998 . I understand why this happens but does any one have a suggestion to fix it.

Answer 1

It's a result of IEEE-754 rounding rules, some numbers cannot be represented precisely in two's complement . For example, 1/10 is not precisely representable.

You can add more precision (but not infinite) by using BigDecimal .

BigDecimal oneTenth = new BigDecimal("1").divide(new BigDecimal("10"));
System.out.println(oneTenth);

Which outputs 0.1

Answer 2

使用内部基本2机器表示无法准确表示某些十进制数字。

Answer 3

That's double precision for you. Binary numbers and decimals don't work well together. Unless you are doing something really precise it should be fine, if you are printing it you should use either decimal format or printf.

Answer 4

Value of floating point numbers are not stored directly but with exponential values. You may write 3.1233453456356 as number, but this is stored something like 3 and 2^6 in memory. It tries to store a value as close as your number, but those differences can happen.

Answer 5

It shouldn't be a problem unless you're testing for equality. With floating-point tests for equality you'll need to allow a "delta" so that:

if (a == b)

becomes

if (abs(a-b) < 0.000001)

or a similar small delta value. For printing, limit it to two decimal places and the formatter will round it for you.