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A type-generic array object

All classes in Java are subclasses of the class named Object . This program creates an array object with the declared type being type Object . An array of type Object can be used to store references to objects instantiated from any class.

After creating the array object, this program instantiates three objects of the class String and stores those object's references in the elements of the array. (As I pointed out in the comments, there is a simpler and better way to instantiate String objects, but it wouldn't illustrate my point as well as doing the way that I did.)

Sometimes you need to downcast

Although an array of type Object can be used to store references to objects of any type (including mixed types and references to other array objects) , you will sometimes need to downcast those references back to their true type once you extract them from the array andattempt to use them for some purpose.

Polymorphic behavior applies here

For this case, however, because the toString method is defined in the Object class and overridden in the String class, polymorphic behavior applies and it is not necessary to downcast the references to type String in order to be able to convert them to strings and display them.

Back to Question 11

Answer 10

C. 0 0 10 2 4

Explanation 10

Defer size specification for secondary arrays

It is not necessary to specify the sizes of the secondary arrays when you create a multi-dimensional array in Java. Rather, since the elements in theprimary array simply contain references to other array objects (or null by default) , you can defer the creation of those secondary array objects until later.

Independent array objects

When you do finally create the secondary arrays, they are essentially independent array objects (except for the requirement for type commonality among them) .

Ragged arrays

Each individual secondary array can be of any size, and this leads to the concept of a ragged array . (On a two-dimensional basis, a ragged array might be thought of as a two-dimensional array where each row can have a different numberof columns.)

This program creates, populates, and displays the contents of such a two-dimensional ragged array. Although this program creates a two-dimensionalarray that is triangular in shape, even that is not a requirement. The number of elements in each of the secondary arrays need have no relationship to the numberof elements in any of the other secondary arrays.

Back to Question 10

Answer 9

B. Runtime Error

Explanation 9

NullPointerException

The following code fragment shows that this program attempts to perform an illegal operation on the value accessed from the array object at index 1.

Integer[] A = new Integer[2]; A[0]= new Integer(1); System.out.println(A[1].intValue());

You can't call methods on null references

The reference value that was returned by accessing A[1] is the default value of null. This is the value that was deposited in the element when the array object was created (no other value was ever stored there) . When an attempt was made to call the intValue method on that reference value, the following runtime error occurred

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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