LECTURE 16:ABSTRACT FACTORY PATTERN

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

Abstract Factory defines set of methods Each method is factory for different type

of object Use this pattern to allocate family of

objects Every component within a look-and-feel Level’s collection of snipers, tanks, &

grues Quacking & flying behavior for the ducks

created Abstract Factory is composition of

factories Group related ideas so will be allocated

together

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

Products are supertypes of useful objects But pattern will only return subtypes of

these

Abstract Factory UML

Client uses subclasses of AbstractFactory ConcreteFactorys 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

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 Clearly identified if classes used must

be related

For Next Lecture

Lab #4 available on Angel Lab will be due before lab in two weeks (Fri.

3/9)

Read pages 169-178 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?