How to return a primitive or object value from a static method using Drools Rule Engine?

I have a static calculation method (many more methods like this one) like:

public class ShareCalculator{
    public static double calculateDailyDecDivRate(DeclaredDividend pDeclaredDiv,  
             FundProductDeclaredDividend pFundProductDeclaredDividend)throws FMSCalculationException{

             ...... verify many if, then else conditions ,, etc....
             then return the double value
    }
}

    I plan to utilize Drools Rule Engine ...
    Then my real question is how DO I RETURN THE Primitive or Object value from this method to a calling
    class?

    Does my question make sense?
    Most of the examples I saw on Drools mostly deal with Object with getter/setter type !!!
    How to I use a class with static methods to return values?

    Thanks much.
    _Esam