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Explanation 10

This is an upgrade to the program from Question 9 .

Success at last

The code in the following fragment resolves the compilation problem from Question 8 and the runtime problem from Question 9 .

void doIt(){ char[]ref = {'J','o','e'}; System.out.print(ref);System.out.print(" "); ref[0]= 'T'; ref[1]= 'o'; ref[2]= 'm'; System.out.println(ref);}//end doIt()

Simply initializing the local reference variable named ref satisfies the compiler, making it possible to compile the program.

Initializing the local reference variable named ref with a reference to a valid array object eliminates the NullPointerException that was experienced in Question 9 .

Printing the contents of the array object

The print statement passes the reference variable to the print method. The print method finds that the reference variable refers to a valid object (instead of containing null as was the case in Question 9 ) and behaves accordingly.

The print statement causes the initialized contents of the array object to be displayed. Then those contents are replaced with a new set of characters. The println statement causes the new characters to be displayed.

Back to Question 10

Answer 9

B. Runtime Error

Explanation 9

Purposely initializing a local variable

This is an update to the program from Question 8 . The code in the following fragment solves the compilation problem identified in Question 8 .

void doIt(){ char[]ref = null;

In particular, initializing the value of the reference variable named ref satisfies the compiler and makes it possible to compile the program.

A NullPointerException

However, there is still a problem, and that problem causes a runtime error.

The following statement attempts to use the reference variable named ref to print something on the screen. This results, among other things, in an attemptto call the toString method on the reference. However, the reference doesn't refer to an object. Rather, it contains the value null .

System.out.print(ref);

The result is a runtime error with the following infamous NullPointerException message appearing on the screen:

java.lang.NullPointerException at java.io.Writer.write(Writer.java:107)at java.io.PrintStream.write(PrintStream.java:245) at java.io.PrintStream.print(PrintStream.java:396)at Worker.doIt(Ap159.java:22) at Ap159.main(Ap159.java:15)

Back to Question 9

Answer 8

A. Compiler Error

Explanation 8

Garbage in, garbage out

Earlier programming languages, notably C and C++ allowed you to inadvertently write programs that process the garbage left in memory by previous programsrunning there. This happens when the C or C++ programmer fails to properly initialize variables, allowing them to contain left-over garbage from memory.

Member variables are automatically initialized to default values

That is not possible in Java. All member variables in a Java object are automatically initialized to a default value if you don't write the code toinitialize them to some other value.

Local variables are not automatically initialized

Local variables are not automatically initialized. However, your program will not compile if you write code that attempts to fetch and use a value in a localvariable that hasn't been initialized or had a value assigned to it.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
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
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
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
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
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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