<< Chapter < Page Chapter >> Page >


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

How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
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.
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
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
characteristics of micro business
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
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
how can I make nanorobot?
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
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.
what is the actual application of fullerenes nowadays?
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.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
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?