多态性虚拟功能parta不含录音.pptx

Chapter04+05homepage15.2HowC++implementslatebinding15.3Virtualfunctionconstructor/destructor15.4Purevirtualfunctionsandabstractclasses15.5Summary15PolymorphismVirtualFunctions15.1Polymorphismvirtualfunctions

15.1PolymorphismvirtualfunctionsStatic/earlybinding(binding)polymorphism,virtualfunctionsDynamic/late/runtimebinding

classInstrument{public: voidplay()const{coutInstrument::playendl;}};voidtune(Instrumenti){i.play();}//WindobjectsareInstruments//theyhavethesameinterface:classWind:publicInstrument{public://Redefineinterfacefunction:voidplay()const{coutWind::playendl;}};

voidmain(){Windflute;tune(flute);//Upcasting}Instrument::playTheproblem:ThecallshouldproduceWind::play,butitisInstrument::play.Usingvirtualfunctionstosolvethisproblem.Instrumenti=flute;15.1Polymorphismvirtualfunctions

classInstrument{public: virtualvoidplay()const{coutInstrument::playendl;}};voidtune(Instrumenti){i.play();}//WindobjectsareInstruments(havethesameinterface)classWind:publicInstrument{public://Redefineinterfacefunction:virtualvoidplay()const//no“virtual”isok.{coutWind::playendl;}};voidmain(){Windflute;tune(flute);//Upcasting}Wind::playvirtualtypefunction-name(arguments);15.1Polymorphismvirtualfunctionsvirtualfunction

//Earlybindinglatebinding#includeiostream#includestringusingnamespacestd;classPet{public:virtualstringspeak()const{returnPet::speak;}};classDog:publicPet{public:virtualstringspeak()const{returnDog::speak;}};voidmain(){Dogralph;Pet*p1=ralph;//typeambiguityPetp2=ralph;//typeambiguityPetp3=ralph;//noambiguity//Latebindingforboth:coutp1-speak()endl;coutp2.speak()endl;//Earlybinding:coutp3.speak()endl;}Dog::speakDog::speakPet::spe