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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

How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
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
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
how can I make nanorobot?
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?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
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