在Java中使用哪种舍入模式进行货币操作？

Question

I have read on java site to use BigDecimal for currencies. http://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html

But what rounding mode we should use with? which is the most appropriate one and most widely us

Answer 1

There is no "correct" mode, it depends on the business case. Examples:

• When calculating annual taxes, the fractions are often cut off ( RoundingMode.FLOOR ).
• When calculating a bonus, you might want to always round in favor of the customer ( RoundingMode.CEILING ).
• For taxes on a bill, you usually round HALF_UP
• When doing complex financial simulations, you don't want to round at all.

The documentation of RoundingMode contains a lot of examples how the different modes work.

To get a better answer, you must tell us what you want to achieve.

That said, BigDecimal is the correct type to use in Java because it can preserve any amount of precision plus it lets you chose the rounding mode most suitable for your case.

Answer 2

Most of the time BigDecimal is the only valid choice for currencies. But the choice of rounding strategy is not that obvious.

The default is HALF_EVEN which happens to be a good choice. This algorithm is known as bankers' rounding (see discussion here ).

Another common strategy is HALF_UP which is more intuitive but has slightly worse statistical characteristics.

Also note that in many times (especially in banking and insurances) the rounding strategy will be dictated by business requirements, often different for various use-cases.

Answer 3

Typically you'd use "half up" rounding, like so:

myBigDecimal.setScale(2, RoundingMode.HALF_UP);

This way, you'll round to two decimal places (which most currencies use, eg dollars and cents, obviously there are exceptions), and you'll round values such that half a cent or more will round up while less than half a cent will round down. See the javadoc for more details.

Answer 4

For the financial applications ROUND_HALF_EVEN is the most common rounding mode. That mode avoids bias. But for display you should use NumberFormat class. This class will take care of localization issues for amounts in different currencies. But NumberFormat accepts primitives only. So use last one if you can accept small accuracy change in transformations to a double.

Answer 5

You should never use a decimal type for currencies. Use an integer type. This maintains accuracy buy avoiding rounding error associated with floats

When display an amount then divide by the appropriate factor to get the non-integral portion.