<< Chapter < Page Chapter >> Page >

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

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
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
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
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
hi
Loga
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
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?

Ask