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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

where we get a research paper on Nano chemistry....?
Maira Reply
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..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
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
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
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
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
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
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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