CSC 313 – Advanced Programming Topics

What Is the Factory Method?  Creation details hidden by AbstractCreator  Does effective job of limiting concrete knowledge

Factory Method Intent  Use incomplete types as the declared type of  Local variables, fields, parameters …  Everywhere, since change might occur anywhere  Since it must be concrete, avoid new command  Replace with factory pattern  Design is then much easier to add new classes  Limits changes required when modify existing classes

Factory Method Use/Avoid  Use a factory method pattern when you  Create object, but can choose class instantiated  Hide subclasses of abstract type from client  Must do complex allocation of object stack  Multiple related allocations is also important  Factory patterns so far define 1 factory method  Create 1 type of object (though many subtypes)  Forced linking or chaining allocations impossible

Decorator:Factory::Strategy:?  Factory Method great for decorator pattern  Inheritance-based design of classes in this pattern  Core concept will be wrapped by many decorators  Returns single instance of abstract supertype  But pattern not helpful for Strategy Pattern  Works for single strategy, since need only 1 type  Often allocate & use many strategies, however  Factory needed for each type of strategy, however

Decorator:Factory::Strategy:?

Often Have Related Strategy  Skinnable apps can change look-and-feel  Similar allocations needed for all widgets

Often Have Related Strategy  Skinnable apps can change look-and-feel  Similar allocations needed for all widgets

Often Have Related Strategy  Skinnable apps can change look-and-feel  Similar allocations needed for all widgets

Sets of Choices  Instantiate sets of components to look good  Different set defined by each look-and-feel  Instantiate only from set defined by components  To change skins, must switch set allocating from  More places need this than skinnable apps  Each game level generates class of enemies  Quacking & flying behaviors in SimUDuck  Printing & transmitting behavior of messages in IM  Colors & fonts used in a presentation

Abstract Factory Pattern

Client View of Pattern  Clients use AbstractFactory & ignores details  All of the factory methods declared by this class

Abstract Factory Design  Common code & fields in AbstractFactory  Can be either an abstract class or interface

Abstract Factory UML  Product s are supertypes of useful objects  But pattern will only return subtypes of these

Abstract Factory UML  Client uses subclasses of AbstractFactory  ConcreteFactory s perform actual allocations

Composition over Inheritance  Inheritance makes mixing options easy

Nearly Real Example  Abstract factory generates related types  Building car from parts would be real-life example

Abstract Factory Vitals  Family of related classes from 1 instance  Pattern is also a composition of factory methods  Related or interdependent classes allocated together  Unlike factory method, instantiates multiple types  Skinnable & visual systems clearest example  Scrollbars, tabs, menus, …: many shared concepts  Concrete implementation changes with each look

Abstract Factory Vitals

For Next Lecture  Lab #4 available on Angel  Lab will be due before lab in two weeks (Fri. 3/9)  Read pages in book  How can we make sure only 1 end boss?  What is plural of apocalypse? How to code this?  How are design patterns & Highlander alike?