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This module provides a very brief treatment of exception handling. The topic is discussed in detail in the module titled Java OOP: Exception Handling by Richard Baldwin

Revised: Tue Mar 29 09:51:41 CDT 2016

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This module provides a very brief treatment of exception handling. The topic is discussed in detail in the module titled Java OOP: Exception Handling . The topic is included in this Programming Fundamentals section simply to introduce you to the concept.

Viewing tip

I recommend that you open another copy of this module in a separate browser window and use the following link to easily find and view the listing while you are reading aboutit.



What is an exception?

According to The Java Tutorials , "An exception is an event that occurs during the execution of a program that disrupts the normal flow of instructions."

A very common example of an exception given in textbooks is code that attempts to divide by zero (this is easy to demonstrate) .

Throwing an exception

Common terminology states that when this happens, the system throws an exception . If a thrown exception is not caught , a runtime error may occur.

Purpose of exception handling

The purpose of exception handling is to make it possible for the program to either attempt to recover from the problem, or at worst shut down the program ina graceful manner, whenever an exception occurs.

Java supports exception handling

Java, C++, and some other programming languages support exception handling in similar ways.

In Java, the exception can be thrown either by the system or by code created by the programmer. Thereis a fairly long list of exceptions that will be thrown automatically by the Java runtime system.

Checked exceptions cannot be ignored

Included in that long list of automatic exceptions is a subset known as "checked" exceptions. Checked exceptions cannot be ignored by the programmer. A method must eitherspecify (declare) or catch all "checked" exceptions that can be thrown in order for the program to compile.

An example of specifying an exception

I explain the difference between specifying and catching an exception in Java OOP: Exception Handling . For now, suffice it to say that the code that begins with theword "throws" in Listing 1 specifies (declares) an exception that can be thrown by the code inside the main method.

If this specification is not made, the program will not compile.

Listing 1 . The program named simple1.
/*File simple1.java Copyright 1997, R.G.Baldwin **********************************************************/class simple1 { //define the controlling class public static void main(String[]args) throws java.io.IOException {int ch1, ch2 = '0'; System.out.println("Enter some text, terminate with #"); //Get and save individual byteswhile( (ch1 = System.in.read() ) != '#') ch2 = ch1; //Display the character immediately before the #System.out.println("The char before the # was " + (char)ch2);}//end main }//End simple1 class.

The program in Listing 1 does not throw any exceptions directly nor does it attempt to catch any exceptions. However, it can throw exceptions indirectly through itscall to System.in.read .

Because IOException is a checked exception, the main method must either specify it or catch it . Otherwise the program won't compile.In this case, the main method specifies the exception as opposed to catching it.

Very brief treatment

As mentioned earlier, this is a very brief treatment of a fairly complex topic that is discussed in much more detail in the module titled Java OOP: Exception Handling . The topic was included at this point simply to introduce you to the concept ofexceptions.

Run the program

II encourage you to copy the code from Listing 1 . Compile the code and execute it. Experiment with the code,making changes, and observing the results of your changes. Make certain that you can explain why your changes behave as they do.

Looking ahead

As you approach the end of this group of Programming Fundamentals modules, you should be preparing yourself for the more challenging ITSE 2321 OOPtracks identified below:


This section contains a variety of miscellaneous information.

Housekeeping material
  • Module name: Jb0250: Java OOP: Brief Introduction to Exceptions
  • File: Jb0250.htm
  • Originally published: 1997
  • Published at cnx.org: 11/26/12

Financial : Although the Connexions site makes it possible for you to download a PDF file for thismodule at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should beaware that some of the HTML elements in this module may not translate well into PDF.

I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.

In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. Ineither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please beaware that it is a copy of a module that is freely available on cnx.org and that it was made and published withoutmy prior knowledge.

Affiliation :: I am a professor of Computer Information Technology at Austin Community College in Austin, TX.


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
On having this app for quite a bit time, Haven't realised there's a chat room in it.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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