C-程序设计教学课件CHAPTER-5-CLASSES

C++ProgrammingCHAPTER5CLASSES1

5.1Introduction

5.2ClassesandObjects

5.3ConstructorsandtheDestructor

5.4Composition

5.5Friends25.1IntroductionStructuredProgrammingvs.Object-OrientedProgrammingStructural(Procedural)Object-OrientedPROGRAMPROGRAMFUNCTIONOBJECTOperationsFUNCTIONDataOBJECTFUNCTIONOBJECTOperationsOperationsDataData35.1IntroductionObject-OrientedProgrammingLanguageFeatures1.DataabstractionTgrammermustestablishtheassociationbetweenthemachinemodelandthemodeloftheproblemthatisactuallybeingsolved.45.1IntroductionExample:Dataabstraction-ClockclassClock{public://CodeabstractionvoidSetTime(intNewH,intNewM,intNewS);voidShowTime();private://DataabstractionintHour,Minute,Second;5};5.1Introduction2.InformationhidingInanobject-orientedlanguage,aclassisarmationhiding.InaC++class,wecanusekeywordssuchaspublicandprivatetocontrolaccesstotheclass’spropertiesandoperations.Wecanusethekeywordpublictoexposetheclass’erfaceandthekeywordprivatetohideitsimplementation.65.1IntroductionExample:Informationhiding-ClockclassClock{public:voidSetTime(intNewH,intNewM,intNewS);voidShowTime();private:intHour,Minute,Second;};75.1Introduction3.IpertiesClassescanbestand-aloneortheycanoccurininheritancehierarchies,whichconsistofparent/childrelationshipsamongclasses.85.1Introduction4.PolymorphismThetermpolymorphismmeanshavingmanyforms.Polymorphismallowsimprovedcodeorganizationandreadabilityaswellasthegramsthatcanbe“grown”notonlyduringtheoriginalcreationject,butalsowhennewfeaturesaredesired.95.1IntroductionOOPTermsC++EquivalentsObjectClassobjectorclassinstanceInstancevariablePrivatedatamemberMethodPublicmemberfunctionMessagepassingFunctioncall(toapublicmemberfunction)105.2ClassesandObjectsClassesClassesInC++,aclassisadatatype.Inobject-orienteddesign,aclassisacollectionofobjects.Operties,features,orattributes.115.2ClassesandObjectsClassessyntax:classclassname{public:publicmembers(interface)private:privatemembersprotected:protectedmembers12};5.2ClassesandObjectsClassesInC++,themembervariablesorfieldsarecalleddatamembers.Thefunctionsthatbelongtoaclassarecalledfunctionmembers.Inobject-orientedlanguagesgenerally,suchfunctionsarecalledmethods.135.2ClassesandObjectsClassesExample:classHuman{private:char*Name;//datamemberschar*Id;public:voidSetName(char*cpName);//methodsvoidGetName(char*cpName);voidSetId(char*cpId);voidGetId(char*cpId);14};5.2ClassesandObjectsClassesExample:classClock{public:voidSetTime(intNewH,intNewM,intNewS);voidShowTime();private:intHour,Minute,Second;};155.2ClassesandObjectsClassesvoidClock::SetTime(intNewH,intNewM,intNewS){Hour=NewH;Minute=NewM;Second=NewS;}voidClock::ShowTime(){cout<<Hour<<":"<<Minute<<":"<<Second;16}5.2ClassesandObjectsClassesRemarks:A)Methodscanbeimplementedeitherinsideoroutsidethedeclarationoftheclass.Ifthemethodsareimplementedoutsidetheclass,andscoperesolutionshouldbeused.175.2ClassesandObjectsClassesB)Ifthemethodsareimplementedinsidetheclass,thentheyturntobetheinlinefunctions.Oryoucanusethekeywordinlinetodeclareaninlinefunction.185.2ClassesandObjectsClassesExample:classPoint{public:voidInit(intinitX,intinitY){X=initX;Y=initY;}intGetX(){returnX;}intGetY(){returnY;}private:intX,Y;19};Example:classPoint{inlinevoidPoint::Init(intinitX,intinitY){public:X=initX;Y=initY;voidInit(intinitX,intinitY);intGetX()；intGetY()；}private:inlineintPoint::GetX(){intX,Y;};returnX;}inlineintPoint::GetY(){returnY;}205.2ClassesandObjectsClassesC)Methodscanbedeclaredtobeoverloadingordefaultarguments.215.2ClassesandObjectsObjectsObjectsIfHumanisauser-defineddatatypeinC++,wecandefinedavariablesuchasmaryLeakeytorepresenttheobjectwhobelongstotheclassofhumanbeings.Example:HumanmaryLeakey;//createanobject225.2ClassesandObjectsObjectsRemark:Aebeforethedefinitionofanyobjects.235.2ClassesandObjectsMemberAccessMemberAccessInsidetheclass,membersareaccesseddirectlybynames.Outsidetheclass,publicmembersareaccessedbytheway“object.member”.245.2ClassesandObjectsMemberAccessExample:#include<iostream>spacestd;classClock{voidmain(void){ClockmyClock;......//myClock.SetTime(8,30,30);myClock.ShowTime();};}255.2ClassesandObjectsThisThisObjectsofoneclasshavethereowndatamembersandsharethesamecopyofmethods.265.2ClassesandObjectsThisobject1object2object3data1data2data1data2data1data2method1method2275.2ClassesandObjectsThisEverymethodhaveanthispointer.Thethispointertellspilerwhichobjectaccessthemethod.Example:voidClock::SetTime(intNewH,intNewM,intNewS){this->Hour=NewH;this->Minute=NewM;this->Second=NewS;28}5.3ConstructorsandtheDestructorsConstructorsConstructorsAconstructoristhe.Asuitableconstructorisinvokedautomaticallywheneveraninstanceoftheclassiscreated.29Example:classPerson{public:Person();Person(conststring&n);Person(constchar*n);voidsetName(conststring&n);voidsetName(constchar*n);conststring&getName()const;private:;};30Person::Person(conststring&n){name=n;}Person::Person(constchar*n){name=n;}intmain(){Personanonymous;Personjc(“J.Coltrane”);return0;}315.3ConstructorsandtheDestructorsConstructorsRemarks:A)Ifaconstructorisnotdefined,adefaultconstructorwillbeinvokedautomaticallyforeachobject.B)Aconstructorcanbeinlinefunction,overloadingfunctionanddefaultargumentsfunction.32Example1:#include<iostream>spacestd;classClock{public:Clock(intNewH,intNewM,intNewS);//ConstructorvoidSetTime(intNewH,intNewM,intNewS);voidShowTime();private:intHour,Minute,Second;};33Clock::Clock(intNewH,intNewM,intNewS){Hour=NewH;Minute=NewM;Second=NewS;}voidmain(){Clockc(0,0,0);//Constructorisinvokedc.ShowTime();}34Example2:classClock{public:Clock(intNewH);Clock(intNewH,intNewM);Clock(intNewH,intNewM,intNewS);//Constructorprivate:intHour,Minute,Second;};35Clock::Clock(intNewH,intNewM,intNewS){Clock::Clock(intNewH){Hour=NewH;Minute=0;Second=0;Hour=NewH;Minute=NewM;Second=NewS;}Clock::Clock(intNewH,intNewM)}{voidmain()Hour=NewH;Minute=NewM;Second=0;{Clocka(1);Clockb(1,2);Clockc(1,2,3);}36}5.3ConstructorsandtheDestructorsConstructorsQuestion:Hgramusingdefaultargumentsfunction?375.3ConstructorsandtheDestructorsTheCopyConstructor

CopyconstructorcreatesanewobjectasacopyofanotherTheCopyConstructorobject.Syntax:classClassName{public:ClassName（arguments）；//constructorClassName（ClassName&object）；//copyconstructor...38}；5.3ConstructorsandtheDestructorsTheCopyConstructorClassName::ClassName（ClassName&object）//copyconstructor{//……}395.3ConstructorsandtheDestructorsTheCopyConstructorExample:classPoint{public:Point(intxx=0,intyy=0){X=xx;Y=yy;}Point(Point&p);intGetX(){returnX;}intGetY(){returnY;}private:intX,Y;40};5.3ConstructorsandtheDestructorsTheCopyConstructorPoint::Point(Point&p){X=p.X;Y=p.Y;cout<<"copyconstructorisinvoked."<<endl;}415.3ConstructorsandtheDestructorsTheCopyConstructorRules:A)Ifanobjectisinitializedbyanotherobjectofthesameclass,thecopyconstructorisinvokedautomatically.425.3ConstructorsandtheDestructorsTheCopyConstructorExample:voidmain(void){PointA(1,2);PointB(A);//copyconstructorisinvokedcout<<B.GetX()<<endl;}435.3ConstructorsandtheDestructorsTheCopyConstructorB)Iftheargumentsofthefunctionisanobjectofaclass,thecopyconstructorisinvokedwhenthefunctionisinvoked.445.3ConstructorsandtheDestructorsTheCopyConstructorExample:voidfun1(Pointp){cout<<p.GetX()<<endl;}voidmain(){PointA(1,2);fun1(A);//copyconstructorisinvoked45}5.3ConstructorsandtheDestructorsTheCopyConstructorC)Ifthefunctionreturnsanobjectofaclass,thecopyconstructorisinvoked.465.3ConstructorsandtheDestructorsTheCopyConstructorExample:Pointfun2(){PointA(1,2);returnA;//copyconstructorisinvoked}voidmain(){PointB;B=fun2();47}5.3ConstructorsandtheDestructorsTheCopyConstructorRemarks:TheC++compilerwillstillautomaticallycreateacopyconstructor,defaultprimitivebehavior:abitcopy,ifyoudon’tmakeone.485.3ConstructorsandtheDestructorsTheCopyConstructorExample:Defaultcopyconstructorcanonlycopythemembersoftheobjectbybitcopy.Object1ResourceObject2User-definedcopyconstructorcancopytheresource,too.Object1ResourceObject2Resource495.3ConstructorsandtheDestructorsDestructorsDestructorsThedestructorisautomaticallyinvokedwheneveranobjectbelongingtoaclassisdestroyed.505.3ConstructorsandtheDestructorsDestructorsSyntax:classClassName{public:ClassName（arguments）；ClassName（ClassName&object）；~ClassName();//destructor}；ClassName::~ClassName（）//destructor{//……51}5.3ConstructorsandtheDestructorsDestructorsRemarks:A)Thedestructortakesnoargumentsandcannotbeoverloaded.B)Thedestructorhasnoreturntype.C)TheC++compilerwillautomaticallycreateadestructorifwedon’tmakeit.52Example:#include<iostream>spacestd;classPoint{public:Point::Point(intxx,intyy){Point(intxx,intyy);~Point();//...X=xx;Y=yy;}Point::~Point(){}private:intX,intY;};535.3ConstructorsandtheDestructorsDestructorsCode545.4CompositionYousimplycreateobjectsofyourexistingclassinsidethenewclass.Thisiscalledcompositionbecausethenewclassiscomposedofobjectsofexistingclasses.555.4CompositionExample:classPoint{private:floatx,y;public:Point(floath,floatv);floatGetX(void);loatGetY(void);voidDraw(void);56};5.4CompositionclassLine{private:Pointp1,p2;public:Line(Pointa,Pointb);VoidDraw(void);};575.4CompositionTheConstructorInitializerListWhenanobjectiscreated,pilerguaranteesthatconstructorsforallofitssubobjectsarecalled.Thenewclassconstructordoesn’thavepermissiontoaccesstheprivatedataelementsofthesubobject,soitcan’tinitializethemdirectly.585.4CompositionTheConstructorInitializerListThesolutionissimple:Calltheconstructorforthesubobject.C++providesaspecialsyntaxforthis,theconstructorinitializerlist.595.4CompositionTheConstructorInitializerListSyntax:ClassName::ClassName(argument1，argument2,……):subobject1(argument1)，subobject2(argument2)，......{//……}605.4CompositionOrderofConstructor&DestructorcallsConstructor:1)memberobjectconstructors2)constructoroftheclassDestructor:destructorarecalledinexactlythereverseorderoftheconstructors615.4CompositionOrderofConstructor&DestructorcallsIfthedefaultconstructorisinvoked,thedefaultmemberobjectconstructorsareinvoked,too.625.4CompositionOrderofConstructor&DestructorcallsExample:classPart{public:Part();Part(inti){val=i;}~Part();voidPrint();private:intval;};635.4CompositionOrderofConstructor&DestructorcallsclassWhole{public:Whole();Whole(inti,intj,intk);~Whole();voidPrint();private:Partone;Parttwo;intdata;64};5.4CompositionOrderofConstructor&DestructorcallsWhole::Whole(){data=0;}Whole::Whole(inti,intj,intk):two(i),one(j),data(k){}//...655.5FriendsTheC++languageusesprivateandprotectedtohidetheimplementationoftheclass.Whatifyouwanttoexplicitlygrantaccesstoafunctionthatisn’tamemberofthecurrentclass?665.5FriendsItisaccomplishedbydeclaringthatfunctionafriendinsidethestructuredeclaration.It’simportantthatthefrienddeclarationoccursinsidethestructuredeclarationbec