Avoiding parallel inheritance hierarchies

Question

I have two parallel inheritance chains:

Vehicle <- Car
        <- Truck <- etc.

VehicleXMLFormatter <- CarXMLFormatter
                    <-         


        

Answer 1

You can use Bridge_pattern

Bridge pattern decouple an abstraction from its implementation so that the two can vary independently.

Two orthogonal class hierarchies (The Abstraction hierarchy and Implementation hierarchy) are linked using composition (and not inheritance).This composition helps both hierarchies to vary independently.

Implementation never refers Abstraction. Abstraction contains Implementation interface as a member (through composition).

Coming back to your example:

Vehicle is Abstraction

Car and Truck are RefinedAbstraction

Formatter is Implementor

XMLFormatter, POJOFormatter are ConcreteImplementor

Pseudo code:

 Formatter formatter  = new XMLFormatter();
 Vehicle vehicle = new Car(formatter);
 vehicle.applyFormat();

 formatter  = new XMLFormatter();
 vehicle = new Truck(formatter);
 vehicle.applyFormat();

 formatter  = new POJOFormatter();
 vehicle = new Truck(formatter);
 vehicle.applyFormat();

related post:

When do you use the Bridge Pattern? How is it different from Adapter pattern?