Avoiding parallel inheritance hierarchies

Question

I have two parallel inheritance chains:

Vehicle <- Car
        <- Truck <- etc.

VehicleXMLFormatter <- CarXMLFormatter
                    <-         


        

Answer 1

I want to add generics to Frederiks answer.

public class Car extends Vehicle
{
   public void Accept( VehicleFormatter v )
   {
       v.Visit (this);
   }
}

public class Truck extends Vehicle
{
   public void Accept( VehicleFormatter v )
   {
       v.Visit (this);
   }
}

public interface VehicleFormatter
{
   public void Visit( T v );
}

public class CarXmlFormatter implements VehicleFormatter
{
    //TODO: implementation
}

public class TruckXmlFormatter implements VehicleFormatter
{
    //TODO: implementation
}