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This case violates the rule

In this case, the method named m is defined in the class named B , which is two levels down from the class named Object .

The method named m is neither defined in nor inherited into the class named Object .

When the reference to the object of the class B was assigned to the reference variable of type Object , the type of the reference was automatically converted to type Object .

Therefore, because the reference is type Object , it cannot be used directly to call the method named m .

The solution is a downcast

In this case, the solution to the problem is a downcast.

The code in Listing 6 shows an attempt to solve the problem by casting the reference down the hierarchy to type A .

Listing 6 . Try a downcast to type A.

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

Still doesn't solve the problem

However, this still doesn't solve the problem, and the result is another compiler error.

The method named m is neither defined in nor inherited into the class named A .

Again, it was necessary to convert the statement into a comment in order to cause the program to compile.

What is the problem here?

The problem with this approach is that the downcast simply didn't go far enough down the inheritance hierarchy.

The class named A does not contain a definition of the method named m . Neither does it inherit the method named m . The method named m is defined in class B, which is a subclass of A .

Therefore, a reference of type A is no more useful than a reference of type Object insofar as calling the method named m is concerned.

The real solution

The solution to the problem is shown in Listing 7 .

Listing 7 . Try a downcast to type B.

//Following will compile and run ((B)var).m();

The code in Listing 7 casts (temporarily converts) the reference value contained in the Object variable named var to type B .

The method named m is defined in the class named B . Therefore, a reference of type B can be used to call the method.

The code in Listing 7 compiles and executes successfully. This causes the method named m to execute, producing the following output on the computer screen:

m in class B

A few odds and ends

Before leaving this topic, let's look at a few more issues.

The code in Listing 8 declares and populates a new variable of type B.

Listing 8 . Assign var to v1.

//Following will compile and run B v1 = (B)var;

The code in Listing 8 uses a cast to:

  • Convert the contents of the Object variable to type B
  • Assign the converted reference to the new reference variable of type B .

This is a legal operation. In this class hierarchy, the reference to the object of the class B can be assigned to a reference variable of the types B, A , or Object .

While this operation is legal, it is usually not a good idea to have two different reference variables that contain references to the same object. Inthis case, the variables named var and v1 both contain a reference to the same object.

Cannot be assigned to type C

However, the reference to the object of the class B cannot be assigned to a reference variable of any other type, including type C . An attempt to do so is shown in Listing 9 .

Questions & Answers

find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
Abhi
how do they get the third part x = (32)5/4
kinnecy Reply
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
hmm
Abhi
is it a question of log
Abhi
🤔.
Abhi
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
hii
Uday
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
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
I'm interested in nanotube
Uday
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
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
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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