问题
I have the following code:
BigDecimal result = BigDecimal.ZERO;
result.setScale(2, BigDecimal.ROUND_FLOOR); //1
BigDecimal amountSum;
// amount sum computation
BigDecimal amountByCurrency = amountSum.divide(32); //-0.04
result.add(amountByCurrency); //2
After line //1 scale is still 0. Why? So, the //2 evaluation doesn't affect to the result. What's wrong?
回答1:
The important part of the #setScale documentation is this:
Note that since BigDecimal objects are immutable, calls of this method do not result in the original object being modified, contrary to the usual convention of having methods named setX mutate field X. Instead, setScale returns an object with the proper scale; the returned object may or may not be newly allocated.
(emphasis added)
Therefore, this line in your code won't change the result instance:
result.setScale(2, BigDecimal.ROUND_FLOOR); //1
Either change it to:
result = result.setScale(2, BigDecimal.ROUND_FLOOR);
to overwrite the instance with the new one, or create a new variable and use that instead of result:
BigDecimal scaledResult = result.setScale(2, BigDecimal.ROUND_FLOOR);
Btw: the same applies to this line:
result.add(amountByCurrency); //2
You need to store the returned BigDecimal instance of the #add call in a variable.
回答2:
You have changed the scale of result, but not the scale of amountSum or amountByCurrency, so when you operate with this variables you are working with scale 0.
If I remember well, there is a "global" method to set the default scale when you create a BigDecimal. You should use this method, or set the scale variable by variable.
来源：https://stackoverflow.com/questions/28216251/bigdecimal-scale-not-working