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However, while necessary, that is not sufficient to ensure runtime polymorphic behavior.

Must define or inherit the method

The type of the reference variable must also be the name of a class that either defines or inherits a version of the method that will ultimately becalled on the object.

Since the class named Object does not define (or inherit) the method named m , a reference of type Object does not qualify as a participant in runtime polymorphic behavior in this case. The attempt to use it as a participant results in the compiler error given above.

One additional scenario

Before leaving this topic, let's look at one additional scenario to help you distinguish what is, and what is not, runtime polymorphism. Consider the codeshown in Listing 6 .

Listing 6 . Not polymorphic behavior.

//Instantiate obj of class A var = new A();//Call the method on it ((A)var).m();// Pause until the user presses any key. Console.ReadKey();}//end Main }//end class Polymorph03

A new object of type A

The code in Listing 6 instantiates a new object of the class named A , and stores the object's reference in the original reference variable named var of type Object .

As a side note, this overwrites the previous contents of the reference variable with a new reference and causes the object whose reference waspreviously stored there to become eligible for garbage collection.

Downcast and call the method

Then the code in Listing 6 casts the reference down to type A , (the type of the object to which the reference refers) , and calls the method named m on the downcast reference.

The output

As you would probably predict, this produces the following output on the computer screen:

m in class A

In this case, the version of the method defined in the class named A , (not the version defined in B) was executed.

Not polymorphic behavior

Once again, in my view, this is not runtime polymorphic behavior (at least it isn't a very useful form of polymorphic behavior) . This code simply converts the type of the reference from type Object to the type of the class from which the object was instantiated, and calls one ofits methods. Nothing special takes place regarding a selection among different versions of the method.

Once again, what is runtime polymorphism?

As I have discussed in this module, runtime polymorphic behavior based on inheritance occurs when

  • The type of the reference is a superclass of the class from which the object was instantiated.
  • The version of the method that is executed is the version that is either defined in, or inherited into, the class from which the object wasinstantiated.

And that is probably more than you ever wanted to hear about runtime polymorphism based on inheritance.

A future module will discuss runtime polymorphism based on the C# interface. From a practical viewpoint, you will find the rules to be similar but somewhatdifferent in the case of the C# interface.

Run the program

I encourage you to copy the code from Listing 7 . Use that code to create a C# console project. Compile and run the project. Experiment with the code,making changes, and observing the results of your changes. Make certain that you can explain why your changes behave as they do.

Questions & Answers

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
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
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
Daniel
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
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
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
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
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.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
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.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
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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