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Calling the noarg constructor

The code in the makeObj method of the Worker class attempted to instantiate a new object using the following code:

NewClass obj = new NewClass();

Since the class definition didn't contain a definition for a noarg constructor, the following compiler error was produced by JDK 1.3.

Ap093.java:18: cannot resolve symbol symbol : constructor NewClass() location: class NewClassNewClass obj = new NewClass();

Back to Question 4

Answer 3

C. An Object

Explanation 3

We finally got it right!

Did you identify the errors in the previous two programs before looking at the answers?

This program declares the class named NewClass correctly and uses the new operator correctly in conjunction with the default noarg constructor for the NewClass class to create a new instance of the class (an object) .

Making the class public

One of the things that I could do differently would be to make the declaration for the NewClass class public (as shown in the following code fragment) .

public class NewClass{ public String toString(){return "An Object"; }//end toString()}//end NewClass

I am a little lazy

The reason that I didn't declare this class public (and haven't done so throughout this series of modules) is because the source code for all public classes and interfaces must be in separate files. While that is probably a good requirement for large programming projects, it isoverkill for simple little programs like I am presenting in this group of self-assessment modules.

Dealing with multiple files

Therefore, in order to avoid the hassle of having to deal with multiple source code files for every program, I have been using package-private access for class definitions other than the controlling class (the controlling class is declared public) . Although I won't get into the details at this point, when a class is not declared public, it is common to saythat it has package-private access instead of public access.

Back to Question 3

Answer 2

A. Compiler Error

Explanation 2

Java is a case-sensitive language

Java keywords must be written exactly as specified. The keyword class cannot be written as Class , which is the problem with this program.

The inappropriate use of the upper-case C in the word Class caused the following compiler error.

Ap091.java:25: 'class' or 'interface' expected Class NewClass{

The solution to the problem

This problem can be resolved by causing the first character in the keyword class to be a lower-case character as shown in the following code fragment.

class NewClass{ public String toString(){return "An Object"; }//end toString()}//end NewClass

Back to Question 2

Answer 1

A. Compiler Error

Explanation 1

Instantiating an object

There are several ways to instantiate an object in Java:

  • Use the newInstance method of the class named Class .
  • Reconstruct a serialized object using an I/O readObject method.
  • Create an initialized array object such as {1,2,3}.
  • Create a String object from a literal string such as "A String".
  • Use the new operator.

Of all of these, the last two are by far the most common.

What you cannot do!

You cannot instantiate a new object using code like the following code fragment that was extracted from this program.

NewClass obj = NewClass();

This program produces the following compiler error:

Ap090.java:18: cannot resolve symbol symbol : method NewClass ()location: class Worker NewClass obj = NewClass();

The solution to the problem

This problem can be solved by inserting the new operator to the left of the constructor as shown in the following code fragment.

NewClass obj = new NewClass();

Back to Question 1

-end-

Questions & Answers

what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
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
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
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Maciej
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Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
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what's the easiest and fastest way to the synthesize AgNP?
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Cied
types of nano material
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I start with an easy one. carbon nanotubes woven into a long filament like a string
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many many of nanotubes
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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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