Question

Here is a small currency converter piece of code:

 public enum CurrencyType {

        DOLLAR(1),
        POUND(1.2),
        RUPEE(.25);

        private CurrencyType(double factor) {
            this.factor = factor;
        }
        private double factor; 

        public double getFactor() {
            return factor;
        }

    }

    public class Currency {

        public Currency(double value, CurrencyType type) {
            this.value = value;
            this.type = type;
        }

        private CurrencyType type;
        private double value;

        public CurrencyType getCurrencyType() {
            return type;
        }

        public double getCurrencyValue() {
            return value;
        }

        public void setCurrenctyValue(double value){
            this.value = value;
        }

    }

public class CurrencyConversion {


    public static Currency convert(Currency c1, Currency c2)
            throws Exception {
        if (c1 != null && c2 != null) {
            c2.setCurrenctyValue(c1.getCurrencyValue()
                    * c1.getCurrencyType().getFactor()
                    * c2.getCurrencyType().getFactor());
            return c2;
        } else
            throw new Exception();
    }


}

I would like to improve this code to make it work for different units of conversion, for example: kgs to pounds, miles to kms, etc etc. Something that looks like this:

public class ConversionManager<T extends Convertible> {


    public T convert(T c1, T c2) 
    {
        //return null;
    }
}

Appreciate your ideas and suggestions.

Answer 1

This is the object-oriented way to do it in my opinion. Note that you could templatize on the data type as well but I’ve just used doubles here since they can represent any scalar units. This provides a nice way of handling conversion between units of different metrics as you asked: distance, currency, mass, etc.

public interface Metric {
    public String getReferenceUnit();
}

public class Distance implements Metric {
    public String getReferenceUnit() {
        return new String("Meters");
    }
}

public interface Units<T extends Metric> {
    public double getToReferenceFactor();
}

public class Kilometers implements Units<Distance> {
    public double getToReferenceFactor() {
        return 1000;
    }
}

static <T extends Metric> double convert(Units<T> from, Units<T> to) {
    return from.getToReferenceFactor() * (1.0 / to.getToReferenceFactor());
}