I need to represent some numbers in Java with perfect precision and fixed number of decimal points after decimal point; after that decimal point, I don’t care. (More concretely – money and percentages.)
I used Java’s own BigDecimal now, but I found out, that it’s really slow and it starts to show in my application.
So I want to solve it with a “regular” integers and a fixed-point arithmetics (long integers have big enough precision for my purposes).
Now, I would think that I am not the first one who has this kind of problem and there would be already a library for that, that already has multiplication/division implemented – but it seems that it isn’t.
Now, I very probably can write it myself (and I probably will), but really, am I really the first person that needs this? Isn’t there already some library for that?
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Answer
Are you completely sure BigDecimal is the performance problem? Did you use a profiler to find out? If yes, two options that could help are:
1) Use long and multiply all values by a factor (for example 100 if you are interested in cents).
2) Use a specially designed class that implements something similar to BigDecimal, but using long internally. I don’t know if a good open source library exists (maybe the Java Math Fixed Point Library?). I wrote one such class myself quite a long time ago (2001 I believe) for J2ME. It’s a bit tricky to get right. Please note BigDecimal uses a long internally as well except if high precision is needed, so this solution will only help a tiny bit in most cases.
Using double isn’t a good option in many cases, because of rounding and precision problems.