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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 .


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

anyone know any internet site where one can find nanotechnology papers?
Damian Reply
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
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
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.
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.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
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.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
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