Chapter105:Polymorphism

Section105.1:TypesofPolymorphism

Polymorphism means that a operation can also be applied to values of some other types. There are multiple types of Polymorphism:

• Ad hoc polymorphism:

containsfunctionoverloading.ThetargetisthataMethodcanbeusedwithdifferenttypeswithoutthe needofbeinggeneric.

• Parametric polymorphism:

istheuseofgenerictypes.SeeGenerics

• Subtyping:

hasthetargetinheritofaclasstogeneralizeasimilarfunctionality

Adhocpolymorphism

ThetargetofAdhocpolymorphismistocreateamethod,thatcanbecalledbydifferentdatatypeswithoutaneed oftype-conversioninthefunctioncallorgenerics.Thefollowingmethod(s)sumInt(par1,par2)canbecalledwith differentdatatypesandhasforeachcombinationoftypesaownimplementation:

publicstaticintsumInt(inta,intb)

{

returna+b;

}

publicstaticintsumInt(stringa,stringb)

{

int_a,_b;

if(!Int32.TryParse(a,out_a))

_a=0;

if(!Int32.TryParse(b,out_b))

_b=0;

return_a+_b;

}

publicstaticintsumInt(stringa,intb)

{

int_a;

if(!Int32.TryParse(a,out_a))

_a=0;

return_a+b;

}

publicstaticintsumInt(inta,stringb)

{

returnsumInt(b,a);

}

publicstaticvoidMain()

{

Console.WriteLine(sumInt(1,2)); // 3
Console.WriteLine(sumInt(“3″,”4”)); // 7
Console.WriteLine(sumInt(“5”,6)); // 11
Console.WriteLine(sumInt(7,”8″)); // 15

}

Here’saexamplecall:

Subtyping

Subtypingistheuseofinheritfromabaseclasstogeneralizeasimilarbehavior:

publicinterfaceCar{

voidrefuel();

}

publicclassNormalCar:Car

{

publicvoidrefuel()

{

Console.WriteLine(“Refuelingwithpetrol”);

}

}

publicclassElectricCar:Car

{

publicvoidrefuel()

{

Console.WriteLine(“Chargingbattery”);

}

}

BothclassesNormalCarandElectricCarnowhaveamethodtorefuel,buttheirownimplementation.Here’sa Example:

publicstaticvoidMain()

{

List<Car>cars=newList<Car>(){

newNormalCar(),

newElectricCar()

};

cars.ForEach(x=>x.refuel());

}

Theoutput will be was following:

Refuelingwithpetrol Charging battery

Section105.2:AnotherPolymorphismExample

Polymorphism is one of the pillar of OOP. Poly derives from a Greek term which means ‘multiple forms’. Below is an example which exhibits Polymorphism. The class Vehicletakes multiple forms as a base class.

TheDerivedclassesDucatiandLamborghiniinheritsfromVehicleandoverridesthebaseclass’sDisplay()

method,todisplayitsownNumberOfWheels.

publicclassVehicle

{

protectedintNumberOfWheels{get;set;}=0;

publicVehicle()

{

}

publicvirtualvoidDisplay()

{

Console.WriteLine($”Thenumberofwheelsforthe{nameof(Vehicle)}is{NumberOfWheels}”);

}

}

publicclassDucati:Vehicle

{

publicDucati()

{

NoOfWheels=2;

}

publicoverridevoidDisplay()

{

Console.WriteLine($”Thenumberofwheelsforthe{nameof(Ducati)}is{NumberOfWheels}”);

}

}

publicclassLamborghini:Vehicle

{

publicLamborghini()

{

NoOfWheels=4;

}

publicoverridevoidDisplay()

{

Console.WriteLine($”Thenumberofwheelsforthe{nameof(Lamborghini)}is

{NumberOfWheels}”);

}

}

BelowisthecodesnippetwherePolymorphismisexhibited.TheobjectiscreatedforthebasetypeVehicleusinga variablevehicleatLine1.ItcallsthebaseclassmethodDisplay()atLine2anddisplaytheoutputasshown.

staticvoidMain(string[]args)

{

Vehiclevehicle=newVehicle(); //Line 1
vehicle.Display(); //Line 2
vehicle=newDucati(); //Line 3
vehicle.Display(); //Line 4
vehicle=newLamborghini(); //Line 5
vehicle.Display(); //Line 6

}

AtLine3,the vehicleobjectispointedtothederivedclassDucatiandcallsitsDisplay()method,whichdisplays theoutputasshown.Herecomesthepolymorphicbehavior,eventhoughtheobjectvehicleisoftypeVehicle,it callsthederivedclassmethodDisplay()asthetypeDucatioverridesthebaseclassDisplay()method,sincethe

vehicleobjectispointedtowardsDucati.

ThesameexplanationisapplicablewhenitinvokestheLamborghinitype’sDisplay()method. The Output is shown below

ThenumberofwheelsfortheVehicleis0 // Line 2

The number of wheels for the Ducati is 2 // Line 4

The number of wheels for the Lamborghini is 4 // Line 6