软件工程与计算16 Design Patterns.pptVIP

*makeconstructor(s)privatesothattheycannotbecalledfromoutsidedeclareasinglestaticprivateinstanceoftheclasswriteapublicgetInstance()orsimilarmethodthatallowsaccesstothesingleinstancepossiblyprotect/synchronizethismethodtoensurethatitwillworkinamulti-threadedprogramImplementingSingletonconsiderasingletonclassRandomGeneratorthatgeneratesrandomnumberspublicclassRandomGenerator{privatestaticRandomGeneratorgen;publicstaticRandomGeneratorgetInstance(){if(gen==null)gen=newRandomGenerator();returngen;}privateRandomGenerator(){}publicdoublenextNumber(){returnMath.random();}}SingletonexampleSingleton模式体现了哪些思想？封装(信息隐藏：外部抽象与内部结构)Principle#1最小化访问实现软件需求需要的是“对象创建方法”，不是“构造方法”如果“构造方法”与“对象创建方法”效果相同，可以直接替代如果“构造方法”与“对象创建方法”效果不同，需要将“对象创建方法”作为外部表现，并加工“构造方法”以实现内部结构操作符重载？有没有违反：GlobalVariablesConsiderHarmful？Objectcreation:Complex(2)

Scenario2:typevariations需要改进吗？EncapsulatingobjectcreationFactoryFactory:aclasswhich’sresponsibilityistocreatingotherclasswithvarytypesFactory体现了哪些思想？Donotrepeat！封装（信息隐藏）：将对象创建抽象为单独职责，并隐藏创建细节有利于对象创建的变更特别是ConditionalStatementsAMorecomplexscenario:typevariationsApplicationnewDocument()openDocument()Documentsave()print()docsMyDocumentMyApplicationcreatesApplicationclassisresponsibleforcreation(andmanagement)ofDocuments Problem:Applicationclassknows:WHENanewdocumentshouldbecreatedApplicationclassdoesn’tknow:WHATKINDofdocumenttocreateDocumentdoc=newDocument();docs.add(doc);doc.open();AMorecomplexscenario:typevariationsSolution:Applicationdefinesavirtualfunction,createDocument()MyApplicationmakessurethatcreateDocument()willcreateaproduct(Document)ofthecorrecttype.Documentdoc=createDocument();docs.add(doc);doc.open();ApplicationcreateDocument()newDocument()openDocument()Documentsave()pri