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Back to Question 6

Answer 5

B. Runtime Error

Explanation 5

ClassCastException

There are some situations involving casting where the compiler cannot identify an erroneous condition that is later identified by the runtime system.This is one of those cases.

This program begins with an array of type double []. Thereference to that array is converted to type Object . Then it is cast to type String []. All of these operations are allowed bythe compiler.

However, at runtime, the runtime system expects to find references to objects of type String in the elements of the array. What it finds instead is values of type double stored in the elements of the array.

As a result, a ClassCastException is thrown. Since it isn't caught and handled by the program, the program terminateswith the following error message showing on the screen.

java.lang.ClassCastException: [D at Worker.doArrays(Ap068.java:17)at Ap068.main(Ap068.java:6)

Back to Question 5

Answer 4

C. 1.0 2.0

Explanation 4

Finally, we got it right

Finally, we managed to get it all together. The program compiles and executes correctly. This program illustrates the assignment of an array object'sreference to a reference variable of type Object , and the casting of that reference of type Object back to the correct array type in order to gain access to the elements in the array.

But don't go away, there is a lot more that you need to know about arrays in Java. We will look at some of those things in the questions that follow.

Back to Question 4

Answer 3

A. Compiler Error

Explanation 3

Must use the correct cast syntax

While it is possible to store an array object's reference in a reference variable of type Object , and later cast it back to an array type to gain access to the elements in the array, you must use the correctsyntax in performing the cast. This is not the correct syntax for performing that cast. It is missing the empty square brackets required to indicate a reference to an array object.

A portion of the compiler error produced by JDK 1.3 is shown below:

Ap066.java:17: inconvertible types found : java.lang.Objectrequired: double double C = (double)B;

Back to Question 3

Answer 2

A. Compiler Error

Explanation 2

Must cast back to an array type

This program illustrates another very important point. Although you can assign an array object's reference to a reference variable of type Object , you cannot gain access to the elements in the array while treating it as type Object . Instead, you must cast it back to an array type before you can gain access to the elements in the array object.

A portion of the compiler error produced by JDK 1.3 is shown below:

Ap065.java:18: array required, but java.lang.Object found B[0]+ " " + B[1]);

Back to Question 2

Answer 1

C. I'm OK

Explanation 1

Assigning array reference to type Object

This program illustrates a very important point. You can assign an array object's reference to an ordinary reference variable of type Object . Note that I didn't say Object[] . The empty square brackets are not required when the type is Object .

Standard containers or collections

Later on, when we study the various containers in the Java class libraries (see the Java Collections Framework) , we will see that they store references to all objects, including array objects, as type Object . Thus, if it were not possible to store a reference to an array object in a reference variable of type Object , it would not be possible to use the standard containers to store references to array objects.

Because it is possible to assign an array object's reference to a variable of type Object , it is also possible to store array object references in containers of type Object .

Back to Question 1

-end-

Questions & Answers

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
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
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?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
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
yes
Asali
I'm not good at math so would you help me
Samantha
what is the problem that i will help you to self with?
Asali
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
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
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
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
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
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
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
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
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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