<< Chapter < Page Chapter >> Page >
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

what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
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
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
how can I make nanorobot?
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

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
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Object-oriented programming (oop) with java' conversation and receive update notifications?