软件设计模式-体系结构-PPT讲稿 0-Software-Design-Patterns-20121030 lec1_FactoryMethod-Creational.ppt

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1、Lecture1TheFactoryMethodPattern工厂方法模式有的工厂生产飞机，有的工厂生产汽车，听说过有生产类的对象的工厂吗？本讲讲述的工厂方法模式专门生产对象。1ContentsofthislectureIntroductionofthefactorymethodpatternTheoryofthesimplefactorymethodPatternanddesignexamplesTheoryofthefactorymethodpatternanddesignexamplesFurtherdiscus

2、sionofthefactorymethodpattern2IntroductionoftheFactoryMethodPattern3IntroductiontoFactoryMethodPattern问题：怎样调用类中的一个方法？Howtoinvokeamethodinaclass?Ifanapplicationobjectknowstheexactmethoditneeds,itcandirectlyinstantiatetheclassfromtheclasshierarchythatcontainstheme

3、thod.Seeexamplebelow.4Car+buyCar()+buyParts()Lincoln+buyCar()+buyParts()Cadillac+buyCar()+buyParts()Buick+buyCar()+buyParts()ClientobCar:CarMain()ClientObjectDirectlyAccessingaClassHierarchyIntroductiontoFactoryMethodPatternCarmyCar;myCar=newLincoln();myCar.buyC

4、ar();5新的情况：1）如果一个类的结构有很多子类2）你不知道该准确地调用哪一个怎么办呢？？？IntroductiontoFactoryMethodPattern6Question:Howtoinvokeamethodinaclasshierarchythatcontainsmanysubclassesandyoudon’tknowexactlywhichonetoselect?Thechoicemaydependon:运行状态.Thestateoftherunningapplication(inputfromuse

5、rs)应用配置设置.ApplicationconfigurationsettingsInsuchcases,anapplicationobjectneedstouseconditionalstatementstoinstantiateanappropriateclassfromthehierarchytoaccessitsservicesIntroductiontoFactoryMethodPattern7Anapplicationobjectneedstoimplementtheclassselectioncrite

6、riatoinstantiateanappropriateclassfromthehierarchytoaccessitsservicesClientobCar:CarMain()If(usrChoice==1){obCar=newLincoln(model);obCar.buyCar();}elseif(usrChoise==2){obCar=newCadillac(model)obCar.buyCar();}Car+buyCar()+buyParts()Lincoln+buyCar()+buyParts()Cadi

7、llac+buyCar()+buyParts()Buick+buyCar()+buyParts()IntroductiontoFactoryMethodPattern8该设计的缺点：Thistypeofdesignhasthefollowingdisadvantages:Highcoupling（高耦合）.Becauseeveryapplicationobjectthatintendstousetheservicesofferedbytheclasshierarchyneedstoimplementtheclassse

8、lectioncriteria,itresultsinahighdegreeofcouplingbetweenanapplicationobjectandtheserviceproviderclasshierarchy.IntroductiontoFactoryMethodPattern9Inelegantstatement(难看