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Label[] A = new Label[2];

Elements initialized to null

This is a two-element array. When first created, it contains two elements, each having a default value of null . What this really means is that the reference values stored in each of the two elements don't initially refer toany object.

Populate the array elements

The next fragment creates two instances (objects) of the Label class and assigns those object's references to the two elements in the arrayobject. This is perfectly valid.

A[0] = new Label("O");A[1] = new Label("K");

You cannot add reference values

The problem arises in the next fragment. Rather than dealing with the object's references in an appropriate manner, this fragment attempts toaccess the text values of the two reference variables and concatenate those values.

System.out.println(A[0] + A[1]);

The compiler produces the following error message:

Ap055.java:14: error: bad operand types for binary operator '+' System.out.println(A[0]+ A[1]);^ first type: Labelsecond type: Label 1 error

This error message is simply telling us that it is not legal to add the values of reference variables.

Not peculiar to arrays

This problem is not peculiar to arrays. You would get a similar error if you attempted to add two reference variables even when they aren't stored in anarray. In this case, the code to access the values of the elements is good. The problem arises when we attempt to do something illegal with those values afterwe access them.

Usually two steps are required

Therefore, except in some special cases such as certain operations involving the wrapper classes, to use Java arrays with types other than the primitive types, whenyou access the value stored in an element of the array (a reference variable) you must perform only those operations on that reference variable that are legalfor an object of that type. That usually involves two steps. The first step accesses the reference to an object. The second step performs some operation onthe object.

Back to Question 7

Answer 6

C. 3

Explanation 6

Once you create an array object for a primitive type in Java, you can treat the elements of the array pretty much as you would treat the elements of anarray in other programming languages. In particular, a statement such the following can be used to assign a value to an indexed element in an arrayreferred to by a reference variable named A .

A[1] = 2;

Similarly, when you reference an indexed element in an expression such as the following, the value stored in the element is used to evaluate the expression.

System.out.println(A[0] + A[1]);

For all Java arrays, you must remember to create the new array object and to store the array object's reference in a reference variable of the correct type. Then you can use the reference variable to gain access to the elements inthe array.

Back to Question 6

Answer 5

B. Runtime Error

Explanation 5

Good fences make good neighbors

One of the great things about an array object in Java is that it knows how to protect its boundaries.

Unlike some other currently popular programming languages, if your program code attempts to access a Java array element outside its boundaries, anexception will be thrown. If your program doesn't catch and handle the exception, the program will be terminated.

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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