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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.

Preview

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

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
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
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
hi
Loga
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
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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