Fraction

[Joe Darcy]

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