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Ap124.java:19: Base is abstract; cannot be instantiated Base myVar = new Base();

Back to Question 5

Answer 4

C. A

Explanation 4

An abstract class with an abstract method

This program illustrates the use of an abstract class containing an abstract method to achieve polymorphic behavior .

The following code fragment shows an abstract class named Base that contains an abstract method named test .

abstract class Base{ abstract public void test();}//end class Base

Extending abstract class and overriding abstract method

The class named A , shown in the following fragment extends the abstract class named Base and overrides the abstract method named test .

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

Can store a subclass reference as a superclass type

Because the class named A extends the class named Base , a reference to an object instantiated from the class named A can be stored in a reference variable of the declared type Base . No cast is required in this case.

Polymorphic behavior

Furthermore, because the class named Base contains the method named test , (as an abstract method) , when the method named test is called on a reference to an object of the class named A , stored in a reference variable of type Base , the overridden version of the method as defined in the class named A will actually be called. This is polymorphic behavior.

(Note, however, that this example does little to illustrate the power of polymorphic behavior because only one class extends the class named Base and only one version of the abstract method named test exists. Thus, the system is not required to select among two or more overridden versionsof the method named test .)

The important code

The following code fragment shows the instantiation of an object of the class named A and the assignment of that object's reference to a reference variable of type Base . Then the fragment calls the method named test on the reference variable.

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

This causes the overridden version of the method named test , shown in the following fragment, to be called, which causes the letter A to be displayed on the standard output device.

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

Back to Question 4

Answer 3

A. Compiler Error

Explanation 3

Classes can be final or abstract, but not both

A class in Java may be declared final . A class may also be declared abstract . A class cannot be declared both final and abstract .

Behavior of final and abstract classes

A class that is declared final cannot be extended. A class that is declared abstract cannot be instantiated. Therefore, it must be extended to be useful.

An abstract class is normally intended to be extended.

Methods can be final or abstract, but not both

A method in Java may be declared final . A method may also be declared abstract . However, a method cannot be declared both final and abstract .

Behavior of final and abstract methods

A method that is declared final cannot be overridden. A method that is declared abstract must be overridden to be useful.

Questions & Answers

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
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
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
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
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
How can I make nanorobot?
Lily
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
how can I make nanorobot?
Lily
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
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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