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In other words, the behavior of the method named test , when called on a reference to an object of type A , is different from the behavior of the method named test when called on a reference to an object of type B .

The method definitions

The definitions of the two classes named A and B , along with the two versions of the overridden method named test are shown in the following fragment.

class A extends Base{ public void test(){System.out.print("A "); }//end test()}//end class A class B extends Base{public void test(){ System.out.print("B ");}//end test() }//end class B

Store a subclass object's reference as a superclass type

The program declares a reference variable of type Base , instantiates a new object of the class named A , and assigns that object's reference to the reference variable of type Base . Then it calls the method named test on that reference as shown in the following fragment.

Base myVar = new A(); myVar.test();

Polymorphic behavior applies

Simple polymorphic behavior causes the overridden version of the method named test , defined in the class named A , (as opposed to the versions defined in class Base or class B ) to be executed. This causes the letter A followed by a space character to be displayed on the standard output device.

Store another subclass object's reference as superclass type

Then the program instantiates a new object from the class named B , and assigns that object's reference to the same reference variable, overwriting thereference previously stored there. (This causes the object whose reference was previously stored in the reference variable to become eligible for garbagecollection in this case.)

Then the program calls the method named test on the reference as shown in the following fragment.

myVar = new B(); myVar.test();

Polymorphic behavior applies again

This time, simple polymorphic behavior causes the overridden version of the method named test , defined in the class named B , (as opposed to the versions defined in class Base or class A ) to be executed. Thiscauses the letter B followed by a space character to be displayed on the standard output device.

Once again, what is runtime polymorphic behavior?

With runtime polymorphic behavior, the method selected for execution is based, not on the type of the reference variable holding the reference to theobject, but rather on the actual class from which the object was instantiated.

If the method was properly overridden, the behavior exhibited by the execution of the method is appropriate for an object of the class from which theobject was instantiated.

Back to Question 10

Answer 9

D. A

Explanation 9

Compiles and executes successfully

This program compiles and executes successfully causing the version of the method named test , which is overridden in the class named A to be executed. That overridden method is shown in the following fragment.

class A extends Base{ public void test(){System.out.print("A ");}//end test() }//end class A

So, what is the issue here?

The purpose of this program is to determine if you understand polymorphic behavior and the role of downcasting. Consider the following fragment taken fromthe program in Question 8 .

Questions & Answers

Application of nanotechnology in medicine
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.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
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
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
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
hi
Loga
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
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