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Why defer the decision?

The decision cannot be made at compile time because the compiler has no way of knowing (when the program is compiled) the actual type of the object whose reference will be stored in the reference variable.

For example, the type of the object might be the result of a choice made at runtime by a human user among several different possible choices.

Could be either type

For the situation described earlier, that object could just as easily be of type SuperClass as of type SubClass . In either case, it would be valid to assign the object's reference to the same superclassreference variable.

If the object were of the SuperClass type, then a call to the method named method on the reference would cause the version of the method defined in SuperClass , and not the version defined in SubClass , to be executed.

One more time -- the version that is executed is determined by the type of the object and not by the type of the reference variable containingthe reference to the object.


From a practical programming viewpoint, polymorphism manifests itself in three distinct forms in C#:

  • Method overloading
  • Method overriding through class inheritance
  • Method overriding through the C# interface inheritance

I covered method overloading as one form of polymorphism (compile-time polymorphism) in an earlier module.

I will begin the discussion of runtime polymorphism through method overriding and class inheritance in this module. I will cover interfaces in a futuremodule.

Discussion and sample code

Let's examine a sample program that illustrates runtime polymorphism using class inheritance and overridden methods. The name of theprogram is Polymorph03 . A complete listing of the program is provided in Listing 7 near the end of the module.

The class named A

I will discuss this program in fragments. Listing 1 shows the definition of a class named A , which extends the class named Object by default.

Listing 1 . Class A.

using System; class A {public virtual void m() { Console.WriteLine("m in class A");}//end method m() }//end class A

The class named A defines a simple method named m .

A virtual method

Note that the method named m is declared to be virtual . This means that it is allowable to override this method in a subclass.

If you come from a Java programming background, you will note that this is the reverse of the situation in Java. In Java, all methods are virtualby default unless they are declared to be final.

Behavior of the virtual method

The behavior of the virtual method, as defined in the class named A , is to display a message indicating that it has been called, and that it isdefined in the class named A .

This message will allow us to determine which version of the method is executed in each case discussed later.

The class named B

Listing 2 shows the definition of a class named B that extends the class named A.

Listing 2 . Class B.

class B : A { public override void m() {Console.WriteLine("m in class B"); }//end method m()}//end

The class named B overrides (redefines) the method named m , which it inherits from the class named A .

Questions & Answers

do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Xna game studio. OpenStax CNX. Feb 28, 2014 Download for free at https://legacy.cnx.org/content/col11634/1.6
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