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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

who was the first nanotechnologist
Lizzy Reply
technologist's thinker father is Richard Feynman but the literature first user scientist Nario Tagunichi.
Norio Taniguchi
I need help
anyone have book of Abdel Salam Hamdy Makhlouf book in pdf Fundamentals of Nanoparticles: Classifications, Synthesis
Naeem Reply
what happen with The nano material on The deep space.?
pedro Reply
It could change the whole space science.
the characteristics of nano materials can be studied by solving which equation?
sibaram Reply
plz answer fast
synthesis of nano materials by chemical reaction taking place in aqueous solvents under high temperature and pressure is call?
hydrothermal synthesis
how can chip be made from sand
Eke Reply
is this allso about nanoscale material
are nano particles real
Missy Reply
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
where is the latest information on a no technology how can I find it
where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
has a lot of application modern world
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
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
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
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
STM - Scanning Tunneling Microscope.
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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