软件设计模式-体系结构-PPT讲稿 0-Software-Design-Patterns-20121030 Lec3 Singleton Pattern-Creational.ppt

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1、Lecture3SingletonPattern(Creational)单例模式Yushan(Michael)Sun2012-10-23Contents1)TheConceptoftheSingletonPattern2)ExampleofUsingtheSingletonPattern3)TheSingletonPatterninMulti-threadProgrammingSingletonPattern(Creational)单例模式TheConceptoftheSingletonPatternTheConceptoftheSingletonPat

2、ternReallifeexamples:OnecountryhasonlyonepresidentAcompanyhasonlyonegeneralmanagerAhusbandhasonlyonewifeOnebankaccounthasonlyonecreditcard现实世界的单例的例子软件中的单例情况Insoftwaredesign，someclassesmayonlyhaveoneinstance,thatis,onecancreateonlyoneobjectforoneclassandonecannotcreatetwoobjects.A

3、systemmayhaveonlyoneglobalobjecttocoordinatethewholebehaviorofthesystem.Example:Inaserverprogram,theconfigurationinformationisputintoafile,whichisreadbyasingletonobject.OtherobjectscanusethissingletonobjecttogettheconfigurationinformationAcompanycanhavemanyprinters,butprintingman

4、agementsystemhasonlyoneprinttaskcontrolobject,whichmanagesprintqueueanddistributestaskstoprintersTheWindowssystemhasonlyonefilesystemandawindowmanager.TheConceptoftheSingletonPattern怎样确保某个类仅仅能生成一个唯一的实例？Therearetwowaystoguaranteethatoneclasshasonlyoneinstanceandthisinstancecanbeea

5、silyobtained方法1：Onewayisthataprogrammerusescodeinaprogramtomakesurethatonlyoneobjectofaparticularclassbecreated;方法2：TheothermethodiscarefullydesignthestructureofaclassthatallowsonlyoneuniqueinstanceiscreatedtomakesureonlyoneobjectcanbecreatedTheConceptoftheSingletonPatternClientC

6、lassSingletonClass只能被创建一个唯一实例的类客户类方法1：在客户类中使用代码确保仅仅有一个SingletonClass的对象被创建方法2：精心设计SingletonClass类，使得仅仅唯一的一个该类的对象能被创建TheConceptoftheSingletonPattern第一种方法不好，因为程序员是很可能疏忽，而导致第二个实例被创建。第二种方法是从根本上保证仅仅有一个实例被创建的有效方法。这就是本节所讲述的实例模式所要表述的内容。TheConceptoftheSingletonPatternTheintentofthesinglet

7、onpattern：toguaranteethatoneclasshasonlyauniqueinstanceandprovideaglobalaccesspointforit.实现单例模式的思想：Inordertopreventclientprogramfromusingtheconstructortocreatemultipleobjects,theconstructorcanbeclaimedasprivatesothenoclientprogramcanuseittocreateanyobject问题：Iftheconstructorisclai

8、medasprivatetypethennoclientprogramcanus