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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

what is math number
Tric Reply
x-2y+3z=-3 2x-y+z=7 -x+3y-z=6
Sidiki Reply
Need help solving this problem (2/7)^-2
Simone Reply
x+2y-z=7
Sidiki
what is the coefficient of -4×
Mehri Reply
-1
Shedrak
the operation * is x * y =x + y/ 1+(x × y) show if the operation is commutative if x × y is not equal to -1
Alfred Reply
An investment account was opened with an initial deposit of $9,600 and earns 7.4% interest, compounded continuously. How much will the account be worth after 15 years?
Kala Reply
lim x to infinity e^1-e^-1/log(1+x)
given eccentricity and a point find the equiation
Moses Reply
12, 17, 22.... 25th term
Alexandra Reply
12, 17, 22.... 25th term
Akash
College algebra is really hard?
Shirleen Reply
Absolutely, for me. My problems with math started in First grade...involving a nun Sister Anastasia, bad vision, talking & getting expelled from Catholic school. When it comes to math I just can't focus and all I can hear is our family silverware banging and clanging on the pink Formica table.
Carole
I'm 13 and I understand it great
AJ
I am 1 year old but I can do it! 1+1=2 proof very hard for me though.
Atone
hi
Adu
Not really they are just easy concepts which can be understood if you have great basics. I am 14 I understood them easily.
Vedant
hi vedant can u help me with some assignments
Solomon
find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
I know this work
salma
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
Abhi
If f(x) = x-2 then, f(3) when 5f(x+1) 5((3-2)+1) 5(1+1) 5(2) 10
Augustine
how do they get the third part x = (32)5/4
kinnecy Reply
make 5/4 into a mixed number, make that a decimal, and then multiply 32 by the decimal 5/4 turns out to be
AJ
how
Sheref
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
hmm
Abhi
is it a question of log
Abhi
🤔.
Abhi
I rally confuse this number And equations too I need exactly help
salma
But this is not salma it's Faiza live in lousvile Ky I garbage this so I am going collage with JCTC that the of the collage thank you my friends
salma
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
hii
Uday
hi
salma
hi
Ayuba
Hello
opoku
hi
Ali
greetings from Iran
Ali
salut. from Algeria
Bach
hi
Nharnhar
A soccer field is a rectangle 130 meters wide and 110 meters long. The coach asks players to run from one corner to the other corner diagonally across. What is that distance, to the nearest tenths place.
Kimberly Reply
Jeannette has $5 and $10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
August Reply
What is the expressiin for seven less than four times the number of nickels
Leonardo Reply
How do i figure this problem out.
how do you translate this in Algebraic Expressions
linda Reply
why surface tension is zero at critical temperature
Shanjida
I think if critical temperature denote high temperature then a liquid stats boils that time the water stats to evaporate so some moles of h2o to up and due to high temp the bonding break they have low density so it can be a reason
s.
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
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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