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Listing 1 . Source code for class A.

using System; class A {//this class is empty }//end class A

The class named A is empty. It was included in this example for the sole purpose of adding a layer of inheritance to the classhierarchy.

The class named B

Listing 2 shows the definition of the class named B . This class extends the class named A as indicated by the colon that joins the B and the A on the first line.

Listing 2 . Source code for class B.

class B : A { public void m() {Console.WriteLine("m in class B"); }//end method m()}//end class B

The method named m

The class named B defines a method named m . The behavior of the method is simply to display a message each time it iscalled.

The class named C

Listing 3 shows the definition of the class named C , which also extends Object by default.

Listing 3 . Source code for class C.

class C { //this class is empty}//end class C

The class named C is also empty. It was included in this example as a sibling class for the class named A . Stated differently, it was included as a class that is not in the ancestral line ofthe class named B .

The driver class

Listing 4 shows the beginning of the driver class named Polymorph02 , which also extends Object by default.

Listing 4 . Beginning of the class named Polymorph02.

public class Polymorph02 { public static void Main() {Object var = new B();

An object of the class named B

This code instantiates an object of the class B and assigns the object's reference to a reference variable of type Object .

Let me repeat what I just said for emphasis. The reference to the object of type B was not assigned to a reference variable of type B . Instead, it was assigned to a reference variable of type Object .

This assignment is allowable because Object is a superclass of B . In other words, the reference to the object of the class B is assignment-compatible with a reference variable of the type Object .

Automatic type conversion

In this case, the reference of type B is automatically converted to type Object and assigned to the reference variable of type Object .

Note that the use of a cast operator was not required in this assignment.

Only part of the story

However, assignment compatibility is only part of the story. The simple fact that a reference is assignment-compatible with a reference variable of a giventype says nothing about what can be done with the reference after it is assigned to the reference variable.

An illegal operation

For example, in this case, the reference variable that was automatically converted to type Object cannot be used directly to call the method named m on the object of type B. This is indicated in Listing 5 .

Listing 5 . Try to call method m on variable var.

//Following will not compile //var.m();

A compiler error

An attempt to call the method named m on the referencevariable of type Object in Listing 5 resulted in the following compiler error:

error CS0117: 'object' does not contain a definition for 'm'

It was necessary to convert the statement to a comment in order to cause the program to compile successfully.

An important rule

In order to use a reference of a class type to call a method, the method must be defined at or above that class in the class hierarchy. Stated differently,the method must either be defined in, or inherited into that class.

Questions & Answers

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
yes
Asali
I'm not good at math so would you help me
Samantha
what is the problem that i will help you to self with?
Asali
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
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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