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If the boolean value obtained in the above fragment is true, the code instantiates a new object of the IllegalStateException class , and uses the throw keyword to throw an exception of this type.

Program aborts

The program was not designed to gracefully handle such an exception. Therefore the program aborts, displaying the error message shown earlier.

Don't throw an exception

The code in the next fragment shows that if the boolean value tested above is false, the program will display the text OK and run successfully to completion.

}else{ System.out.println("OK");}//end else }//end doIt()

You may need to run the program several times to see both possibilities.

Back to Question 3

Answer 2

The answer is both of the following:

  • D. OK
  • B. Runtime Error

Explanation 2

One cast is allowable ...

It is allowable, but not necessary, to cast the type of an object's reference toward the root of the inheritance hierarchy.

It is also allowable to cast the type of an object's reference along the inheritance hierarchy toward the actual class from which the object wasinstantiated.

Another cast is not allowable ...

However, (excluding interface type casts) , it is not allowable to cast the type of an object's reference in ways that are not related in asubclass-superclass inheritance sense. For example, you cannot cast the type of an object's reference to the type of a sibling of that object.

Two sibling classes

The code in the following fragment defines two simple classes named MyClassA and MyClassB . By default, each of these classes extends the class named Object . Therefore, neither is a superclass of the other. Rather, they are siblings.

class MyClassA{ public String toString(){return "OK "; }//end test()}//end class MyClassA class MyClassB{public String toString(){ return "OK ";}//end test() }//end class MyClassB

Instantiate one object from each sibling class

The code in the next fragment instantiates one object from each of the above classes, and stores references to those objects in reference variables of typeObject.

Then the code causes the overridden toString method of one of the objects to be called by passing that object's reference to the print method.

void doIt(){ Object ref1 = new MyClassA();Object ref2 = new MyClassB(); System.out.print(ref1);

The code in the above fragment causes the text OK to appear on the screen.

Try to cast to a sibling class type

At this point, the reference variable named ref1 holds a reference to an object of type MyClassA . The reference is being held as type Object .

The statement in the next fragment attempts to cast that reference to type MyClassB , which is a sibling of the class named MyClassA .

MyClassB ref3 = (MyClassB)ref1;

A ClassCastException

The above statement causes a ClassCastException to be thrown, which in turn causes the program to abort. The screen output is shown below:

OK java.lang.ClassCastException:MyClassA at Worker.doIt(Ap152.java:24)at Ap152.main(Ap152.java:14)

(Note that the text OK appeared on the screen before the program aborted and displayed diagnostic information on the screen.)

Questions & Answers

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
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
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