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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

how can chip be made from sand
Eke Reply
is this allso about nanoscale material
are nano particles real
Missy Reply
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
where is the latest information on a no technology how can I find it
where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
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..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
has a lot of application modern world
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
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.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
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
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
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
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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