The first and most important rule: use a decimal data type, never ever binary floating-point types. When exactly rounding should be performed can be mandated by regulations, such as the conversion between the Euro and national currencies it replaced. If there are no such rules, I’d do all calculations with high precision, and round only … Read more
As mentioned, the Wikipedia article on IEEE 754 does a good job of showing how floating point numbers are stored on most systems. Now, here are some common gotchas: The biggest is that you almost never want to compare two floating point numbers for equality (or inequality). You’ll want to use greater than/less than comparisons … Read more
Never use a floating point number to represent money. Floating numbers do not represent numbers in decimal notation accurately. You would end with a nightmare of compound rounding errors, and unable to reliably convert between currencies. See Martin Fowler’s short essay on the subject. If you decide to write your own class, I recommend basing … Read more
You can’t use the equals() method to compare BigDecimals, like this assertion does. That is because this equals function will compare the scale. If the scale is different, equals() will return false, even if they are the same number mathematically. You can however use compareTo() to do what you want: As @assylias points out, you … Read more