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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


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

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
okay, so you have 6 raised to the power of 2. what is that part of your answer
I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
I'm not sure why it wrote it the other way
I got X =-6
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
Commplementary angles
Idrissa Reply
im all ears I need to learn
right! what he said ⤴⤴⤴
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
I'm not good at math so would you help me
what is the problem that i will help you to self with?
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
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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