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The override declaration

Note the use of the override declaration in Listing 2 . In C#, if one method overrides another, it is necessary to declare that fact.

Once again, if you come from a Java background, you will note that this is just the reverse of the situation in Java. In Java, a method whose name,return type, and formal argument list matches an inherited method will automatically override the inherited method.

A compiler warning

If you fail to make the override declaration in Listing 2 , you will get a compiler warning that reads something like the following:

warning CS0114: 'B.m()' hides inherited member 'A.m()'. To make the current member override that implementation,add the override keyword. Otherwise add the new keyword.

Overriding versus hiding

I'm not going to get into a discussion of the difference between overriding and hiding in this module. Perhaps I will find the time to provide such adiscussion in a future module.

Behavior of the overridden method

Like the inherited version of the method, the overridden version displays a message indicating that it has been called. However, the message is differentfrom the message displayed by the inherited version discussed above. The overridden version tells us that it is defined in the class named B .

According to the current jargon, the behavior of the overridden version of the method is appropriate for an object instantiated from the classnamed B .

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

The driver class

Listing 3 shows the beginning of the driver class named Polymorph03 .

Listing 3 . Beginning of the driver class.

public class Polymorph03 { public static void Main() {Object var = new B(); //Following will compile and run((B)var).m();

A new object of the class B

The code in the Main method begins by instantiating a new object of the class named B , and assigning the object's reference to a reference variable of type Object .

This is legal because an object's reference can be assigned to any reference variable whose type is a superclass of the class from which the objectwas instantiated. The class named Object is the superclass of all classes.

Downcast and call the method

If you have read the module titled Xna0112-Type Conversion, Casting, and Assignment Compatibility , it will come as no surprise to you that the second statement in the Main method, which casts the reference down to type B and calls the method named m on it, will compile and execute successfully.

Which version was executed?

The execution of the method produces the following output on the computer screen:

m in class B

By examining the output, you can confirm that the version of the method that was overridden in the class named B is the version that was executed.

Why was this version executed?

This should also come as no surprise to you. The cast converts the type of the reference from type Object to type B .

You can always call a public method belonging to an object using a referenceto the object whose type is the same as the class from which the object was instantiated.

Questions & Answers

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.
yes that's correct
I think
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
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
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 did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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