Fraction (original) (raw)

Joe Darcy joe.darcy at oracle.com
Thu Jan 5 23:46:09 UTC 2012

Hello,

On 1/1/2012 8:54 AM, Tom Eugelink wrote:

Hello guys, I was wondering if it was of any interest to OpenJFX to have a calculation class that does not round. I've got "Fraction" laying around, which does math using two BigIntegers, so it never even rounds. The API is roughly equivalent to BigDecimal, so you have methods like add, divide, etc. Any interest in adding such a class to Java?

The BigDecimal class can already preform exact computations. To get exact behavior, use the version of add, subtract, etc. that takes a single BigDecimal argument or the version that takes a BigDecimal argument and a MathContext argument and pass a MathContext object with a precision of 0. Of the four basic arithmetic operations, the most interesting operation is divide since it can result in infinite inputs (fractions that are non-terminating in decimal) from finite inputs while the other operations cannot.

In terms of its representation, BigDecimal class uses a floating-point style scaled representation so that very large or very small numbers that are low-precision don't use a lot of storage.

When doing general computations, there is a need to round result periodically to avoid unbounded growth in the sizes of the numbers being operated on. BigDecimal supports various rounding operations, including rounding to a given number of places after the decimal point and rounding to a given number of total digits. These styles of rounding are relatively easy to understand, but still quite vexing for numerical analysis.

The rounding options I'm familiar with for rational packages are fixed slash vs floating-slash, that is, given constraints on the sizes of the numerator and denominator, return the nearest fraction to the exact result. AFAIK, such system are less studied if not more difficult to work with than traditional rounding.

In short, while there would be some use cases, without additional justification I don't see the need to add a rational number package to the JDK.

Cheers,

-Joe

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