What is difference between Factory and Abstract Factory ?

Question

What is difference between Factory and Abstract Factory design pattern? How to decide which design pattern to use? What is checklist to decide design pattern?

Abhay Shanker · Answer

check the urls http://architects.dzone.com/articles/factory-method-vs-abstract http://www.dofactory.com/topic/1449/what-is-the-difference-between-abstract-factory-and-factory-design-pattern/1623.aspx#p1623 The Factory Method is usually categorised by a switch statement where each case returns a different class using the same root interface so that the calling code never needs to make decisions about the implementation. Think of a credit card validator factory which returns a different validator for each card type. public ICardValidator GetCardValidator (string cardType) { switch (cardType.ToLower()) { case visa: return new VisaCardValidator(); case mastercard: case ecmc: return new MastercardValidator(); default: throw new CreditCardTypeException(Do not recognise this type); } } The Abstract Factory is where you have multiple concrete factory classes (not Factory Methods) derived from one interface which may return many different types from different methods. Think of a chess game manager with a different class for each set of variant rules. public class StandardChessRulesFactory : IChessRulesFactory { public IBoardMapper GetBoardMapper() { return new StandardChessBoardMapper(); } public IKingMover GetKingMover() { return new StandardChessKingMover(); } public IMoveClock GetMoveClock() { return new StandardMoveClock(); } } public class HexagonalChessRulesFactory : IChessRulesFactory { public IBoardMapper GetBoardMapper() { return new HexagonalChessBoardMapper(); } public IKingMover GetKingMover() { return new HexagonalChessKingMover(); } public IMoveClock GetMoveClock() { return new StandardMoveClock(); } } public class SpeedChessRulesFactory : IChessRulesFactory { public IBoardMapper GetBoardMapper() { return new StandardChessBoardMapper(); } public IKingMover GetKingMover() { return new StandardChessKingMover(); } public IMoveClock GetMoveClock() { return new SpeedChessMoveClock(); } } An Abstract Factory much like a Strategy is often selected using a Factory Method but it isn't necessary to combine them so it is its own pattern.