C++面向?qū)ο蟪绦蛟O(shè)計雙語教程（第3版）課件 class 5-classes objects-2

ObjectivesToknowtheUMLdiagram-classdiagramBeawareoftheeffectofconstructorsanddestructorinaclassTobeabletodefineconstructorsanddestructorsandusethemTo

understandthedefinitionofaclassfurther01UMLDiagram04CaseStudy03Destructors02Constructors01UMLDiagramProblem-SolvingCase

Study

1DefineaDateclasswiththeday,monthandyear.Requirement:InputthedataofanobjectOutputthedataoftheobjectReset(modify)thedataoftheobjectGetthedayoftheobjectGetthemonthoftheobjectdataabstractionData:year,month,day-intFunctions(operations):inputoutputresetgetDaygetMonthcheckvoidinput()voidoutput()voidreset()intgetDay()intgetMonth()boolcheck()Problem-SolvingUsingUMLClassDiagramThe

UnifiedModelingLanguage(UML)isageneral-purposedevelopmental,modelinglanguageinthefieldofsoftwareengineeringthatisintendedtoprovideastandardwaytovisualizethedesignasystem.TheUMLdiagramisoftenusedforobject-orienteddesign.The

UML

classdiagramisagraphicalnotationusedtoconstructandvisualizeobjectorientedsystems.AclassdiagramintheUMLisatypeofstaticstructurediagramthatdescribesthestructureofasystembyshowingthesystem’s:classestheirattributes(datamembersinC++)operations/methods(memberfunctionsinC++)therelationshipsamongobjectsProblem-SolvingUsingUMLClassDiagramEncapsulationdataabstractionDate-day:int-month:int-year:int-check():bool+input():void+output():void+reset():void+getDay():int+getMonth():intdatamembers(properties)memberfunctions(Operations)UMLanalysisclass_nameaccessspecifier(-,+)datamemberaccessspecifier(-,+)memberfunctionsclassdiagramdataabstractionData:year,month,day-intFunctions(operations):inputoutputresetgetDaygetMonthcheckvoidinput()voidoutput()voidreset()intgetDay()intgetMonth()boolcheck()intmain(){Datetoday;today.input();today.output();today.reset();cout<<"theDateis"<<today.getMonth()<<"-"<<today.getDay();return0;}Implementationclass

Date{public:voidinput();voidoutput();voidreset();intgetDay();intgetMonth();private:intday,month,year;boolcheck();};Date-day:int-month:int-year:int-check():bool+input():void+output():void+reset():void+getDay():int+getMonth():intInformationhidingimplementationbool

Date::check(){if(day<1||day>31||month<1||month>12||year<1){ cout<<"Invaliddate!\n";return

false;}else return

true;}void

Date::reset(){cout<<"Resetadate\n";input();}int

Date::getMonth(){returnmonth;}int

Date::getDay(){returnday;}void

Date::output(){cout<<year<<"-"<<month<<"-"<<day<<endl;}Implementationvoid

Date::input(){do{cout<<"Entertheyear,monthanddayofadate:\n";cin>>year>>month>>day;}while(!check());}Date-day:int-month:int-year:int-check():bool+input():void+output():void+reset():void+getDay():int+getMonth():int02ConstructorsConstructorsintmain(){Datetoday;today.input();today.output();today.reset();cout<<"theDateis"<<today.getMonth()<<"-"<<today.getDay();return0;}Allocatememoryandinitializedatamembersvoid

Date::input(){do{cout<<"Entertheyear,monthanddayofadate:\n";cin>>year>>month>>day;}while(!check());}ConstructorWhotoallocatememory?Howmuchtoallocatememoryforobject?Howtostoredataofanobject?ConstructorsForexample,Datetoday;Aconstructorisaspecialmemberfunctionthatisautomaticallycalledwheneveraclassobjectiscreated.Aconstructorisrecognizedbyhavingthesamenameas

theclassitself.DefinitionofConstructorsMemberfunctionItsnameisthesameasclass’snameNoreturntypewithinitsdeclaration/definitionNoreturnstatementwithinitsdefinitionclass

Date{public:Date();voidoutput();voidreset();intgetDay();intgetMonth();private:intday,month,year;boolcheck();};constructorofclassDateDate::Date(){do{cout<<"Entertheyear,monthanddayofadate:\n";cin>>year>>month>>day;}while(!check());}Usageof

Constructorsintmain(){Datetoday;Datemybirthday;}classDate{public:Date();//..};Whenaclasshasaconstructor,allobjectsofthatclasswillbeinitializedbyaconstructorcall.OverloadingConstructorsThereareafewconstructorsinaclass.Constructorsobeythesameoverloadingrulesasdootherfunctions.Aslongastheconstructorsdiffersufficientlyintheirparametertypes,thecompilercanselectthecorrectoneforeachuse.

OverloadingConstructorsclassDate{public:

Date(int,int,int);Date(int,int);Date(int);Date();Date(const*char);private:intday,month,year;};intmain(){Datetoday(4);Datejuly4(“July42020”);Datenow;}AfewconstructorsinaclassaredefinedDefaultConstructorsDefaultconstructorsaredefinedinthethreeways.class

Date{public:Date();……intgetMonth();private:intday,month,year;boolcheck();};class

Date{public:Date(int=2020,int=9,int=1);……intgetMonth();private:intday,month,year;boolcheck();};DefaultconstructorDate::Date(){do{ cin>>year>>month>>day;}while(!check());}Date::Date(int

y,int

m,int

d){year=y;month=m;day=d;if(!check())exit(1);}3.Theconstructoriswithdefaultparameters;1.Theconstructorisnotdefinedintheclass;2.Theconstructoriswithoutparameters;class

Date{public:Date();Date(int=2020,int=9,int=1);……intgetMonth();private:intday,month,year;boolcheck();};intmain(){Datetoday(2015);Datetomorrow;return0;}//errorDefaultConstructorsWhenaclasshasmorethanonedefaultconstructor,thisleadstoambiguouscalltooverloadedconstructors.03DestructorsDestructors(析構(gòu)函數(shù))Adestructorisaspecialmemberfunctionthatisautomaticallyinvokedwheneveraclassobjectgoesoutofitsscope.Adestructorisrecognizedbyhavingthesameasthenameofitsclassprefixedbya~.

intmain(){Datetomorrow;return0;}Destructorsclass

Date{public:Date();……intgetMonth();~Date();private:intday,month,year;boolcheck();};destructorMemberfunctionItsnameisthesameasclass’snameprefixedbya~Noreturntypewithinitsdeclaration/definitionNoreturnstatementwithinitsdefinitionNoparameterswithinitsdefinitionDate::~Date(){cout<<"callingthedestructor\n";}intmain(){Datetomorrow;f();return0;}voidf(){Dateday;}OnlyonedestructorinaclassOrdersofConstructorandDestructorCallsAconstructorisimplicitlycalledwhenanobjectofaclassiscreated.Adestructorisimplicitlycalledwhenanobjectgoesoutofscope.Aconstructormakessurethatanobjectisproperlycreatedandinitialized.Conversely,adestructor

makessurethatanobjectisproperlycleanedupbeforeitisdestroyed.OrdersofConstructorandDestructorCallsclass

Date{public:Date(int=2020,int=9,int=1);voidoutput();~Date();private:intday,month,year;};Date::Date(int

y,int

m,int

d){cout<<"callingtheconstructor\n";year=y;month=m;day=d;}Date::~Date(){cout<<"callingthedestructor\n";output();}intmain(){Datetoday(2019);

Datetomorrow(2019,10,24);return0;}Outputresult:callingtheconstructorcallingtheconstructorcallingthedestructor2019-10-24callingthedestructor2020-9-1void

Date::output(){cout<<year<<"-"<<month<<"-"<<day<<endl;}Whentheobjectsarecreatedfromtoptodownin

a

scope,theconstructoriscalledinturn.Whentheobjectsgooutoftheirscope,thedestructorsarecalledinreverseorderofcreatingobjects.04CaseStudyCaseStudy-ProductSalesTotheissueofproductsale,youneedtodo:inputeachproduct'sID,unitprice,sales;(2)calculatetherevenueofallproducts;(3)printsaleinformation.YouanalysethisissuebyusingUMLandwriteoutabstracteddataandfunctions.DataabstractionDat