<< Chapter < Page Chapter >> Page >

Answers

Answer 15

C. 1.0 2.0

Explanation 15

This is an upgrade of the program from Question 14 . This program applies the proper downcast operator to the references extracted from the array of type Object before attempting to call the method named getData on those references. (For more information, see the discussion of Question 14 .)

As a result of applying a proper downcast, the program compiles and runs successfully.

Back to Question 15

Answer 14

A. Compiler Error

Explanation 14

Storing references in a generic array of type Object

This program stores references to two objects instantiated from a new class named MyClass in the elements of an array object of declared type Object . That is OK.

Calling a method on the references

Then the program extracts the references to the two objects and attempts to call the method named getData on each of the references. That is not OK.

Downcast is required

Because the method named getData is not defined in the class named Object , in order to call this method on references extracted from an array of type Object , it is necessary to downcast the references to the class in which the method isdefined. In this case, the method is defined in the new class named MyClass (but it could be defined in an intermediate class in the class hierarchy if the newclass extended some class further down the hierarchy) .

Here is a partial listing of the compiler error produced by this program:

Ap062.java:15: error: cannot find symbol A[0].getData() + " " + ^symbol: method getData() location: class Object

Back to Question 14

Answer 13

D. None of the above.

Explanation 13

The array object of type Object in this program is capable of storing a reference to a new object instantiated from the new class named MyClass . However, because the new class does not override the toString method, when a string representation of the new object is displayed, the stringrepresentation is created using the version of the toString method that is inherited from the Object class. That causes this program to produce an output similar to the following:

Zero 1 MyClass@273d3c

Back to Question 13

Answer 12

C. Zero 1 2.0

Explanation 12

A type-generic array object

As explained in Question 11 , an array object of the type Object is a generic array that can be used to store references to objects instantiated from anyclass.

Storing mixed reference types

This program instantiates objects from the classes String , Integer , and Double , and stores those objects' references inthe elements of an array of type Object . Then the program accesses the references and uses them to display string representations of each of theobjects.

Polymorphic behavior applies

Once again, polymorphic behavior involving overridden versions of the toString method were involved and it was not necessary to downcast the references to their true type to display string representations of the objects.

Back to Question 12

Answer 11

C. Zero One Two

Explanation 11

Storing references to subclass types

When you create an array object for a type defined by a class definition, the elements of the array can be used to store references to objects of that classor any subclass of that class.

Questions & Answers

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
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
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
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
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





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
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Object-oriented programming (oop) with java' conversation and receive update notifications?

Ask