As we all know, exception handling becomes a very handy tool for debugging an application. Rajesh will now explein how one should use Exceptions in C#.
Exception handling is an in built mechanism in .NET framework to detect and handle run time errors. The .NET framework contains lots of standard exceptions. The exceptions are anomalies that occur during the execution of a program. They can be because of user, logic or system errors. If a user (programmer) do not provide a mechanism to handle these anomalies, the .NET run time environment provide a default mechanism, which terminates the program execution.
C# provides three keywords try, catch and finally to do exception handling. The try encloses the statements that might throw an exception whereas catch handles an exception if one exists. The finally can be used for doing any clean up process.
The general form try-catch-finally in C# is shown below
try
{
// Statement which can cause an exception.
}
catch(Type x)
{
// Statements for handling the exception
}
finally
{
//Any cleanup code
}
If any exception occurs inside the try block, the control transfers to the appropriate catch block and later to the finally block.
But in C#, both catch and finally blocks are optional. The try block can exist either with one or more catch blocks or a finally block or with both catch and finally blocks.
If there is no exception occurred inside the try block, the control directly transfers to finally block. We can say that the statements inside the finally block is executed always. Note that it is an error to transfer control out of a finally block by using break, continue, return or goto.
In C#, exceptions are nothing but objects of the type Exception. The Exception is the ultimate base class for any exceptions in C#. The C# itself provides couple of standard exceptions. Or even the user can create their own exception classes, provided that this should inherit from either Exception class or one of the standard derived classes of Exception class like DivideByZeroExcpetion ot ArgumentException etc.
Uncaught Exceptions
The following program will compile but will show an error during execution. The division by zero is a runtime anomaly and program terminates with an error message. Any uncaught exceptions in the current context propagate to a higher context and looks for an appropriate catch block to handle it. If it can’t find any suitable catch blocks, the default mechanism of the .NET runtime will terminate the execution of the entire program.
//C#: Exception Handling
//Author: rajeshvs@msn.com
using System;
class MyClient
{
public static void Main()
{
int x = 0;
int div = 100/x;
Console.WriteLine(div);
}
}
The modified form of the above program with exception handling mechanism is as follows. Here we are using the object of the standard exception class DivideByZeroException to handle the exception caused by division by zero.
//C#: Exception Handling
//Author: rajeshvs@msn.com
using System;
class MyClient
{
public static void Main()
{
int x = 0;
int div = 0;
try
{
div = 100/x;
Console.WriteLine(“This line in not executed”);
}
catch(DivideByZeroException de)
{
Console.WriteLine("Exception occured");
}
Console.WriteLine("Result is {0}",div);
}
}
In the above case the program do not terminate unexpectedly. Instead the program control passes from the point where exception occurred inside the try block to the catch blocks. If it finds any suitable catch block, executes the statements inside that catch and continues with the normal execution of the program statements.
If a finally block is present, the code inside the finally block will get also be executed.
//C#: Exception Handling
//Author: rajeshvs@msn.com
using System;
class MyClient
{
public static void Main()
{
int x = 0;
int div = 0;
try
{
div = 100/x;
Console.WriteLine("Not executed line");
}
catch(DivideByZeroException de)
{
Console.WriteLine("Exception occured");
}
finally
{
Console.WriteLine("Finally Block");
}
Console.WriteLine("Result is {0}",div);
}
}
Remember that in C#, the catch block is optional. The following program is perfectly legal in C#.
//C#: Exception Handling
//Author: rajeshvs@msn.com
using System;
class MyClient
{
public static void Main()
{
int x = 0;
int div = 0;
try
{
div = 100/x;
Console.WriteLine("Not executed line");
}
finally
{
Console.WriteLine("Finally Block");
}
Console.WriteLine("Result is {0}",div);
}
}
But in this case, since there is no exception handling catch block, the execution will get terminated. But before the termination of the program statements inside the finally block will get executed. In C#, a try block must be followed by either a catch or finally block
Multiple Catch Blocks
A try block can throw multiple exceptions, which can handle by using multiple catch blocks. Remember that more specialized catch block should come before a generalized one. Otherwise the compiler will show a compilation error.
//C#: Exception Handling: Multiple catch
//Author: rajeshvs@msn.com
using System;
class MyClient
{
public static void Main()
{
int x = 0;
int div = 0;
try
{
div = 100/x;
Console.WriteLine("Not executed line");
}
catch(DivideByZeroException de)
{
Console.WriteLine("DivideByZeroException" );
}
catch(Exception ee)
{
Console.WriteLine("Exception" );
}
finally
{
Console.WriteLine("Finally Block");
}
Console.WriteLine("Result is {0}",div);
}
}
Catching all Exceptions
By providing a catch block without a brackets or arguments, we can catch all exceptions occurred inside a try block. Even we can use a catch block with an Exception type parameter to catch all exceptions happened inside the try block since in C#, all exceptions are directly or indirectly inherited from the Exception class.
//C#: Exception Handling: Handling all exceptions
//Author: rajeshvs@msn.com
using System;
class MyClient
{
public static void Main()
{
int x = 0;
int div = 0;
try
{
div = 100/x;
Console.WriteLine("Not executed line");
}
catch
{
Console.WriteLine("oException" );
}
Console.WriteLine("Result is {0}",div);
}
}
The following program handles all exception with Exception object.
//C#: Exception Handling: Handling all exceptions
//Author: rajeshvs@msn.com
using System;
class MyClient
{
public static void Main()
{
int x = 0;
int div = 0;
try
{
div = 100/x;
Console.WriteLine("Not executed line");
}
catch(Exception e)
{
Console.WriteLine("oException" );
}
Console.WriteLine("Result is {0}",div);
}
}
Throwing an Exception
In C#, it is possible to throw an exception programmatically. The ‘throw’ keyword is used for this purpose. The general form of throwing an exception is as follows.
throw exception_obj;
For example the following statement throw an ArgumentException explicitly.
throw new ArgumentException(“Exception”);
//C#: Exception Handling:
//Author: rajeshvs@msn.com
using System;
class MyClient
{
public static void Main()
{
try
{
throw new DivideByZeroException("Invalid Division");
}
catch(DivideByZeroException e)
{
Console.WriteLine("Exception" );
}
Console.WriteLine("LAST STATEMENT");
}
}
Re-throwing an Exception
The exceptions, which we caught inside a catch block, can re-throw to a higher context by using the keyword throw inside the catch block. The following program shows how to do this.
//C#: Exception Handling: Handling all exceptions
//Author: rajeshvs@msn.com
using System;
class MyClass
{
public void Method()
{
try
{
int x = 0;
int sum = 100/x;
}
catch(DivideByZeroException e)
{
throw;
}
}
}
class MyClient
{
public static void Main()
{
MyClass mc = new MyClass();
try
{
mc.Method();
}
catch(Exception e)
{
Console.WriteLine("Exception caught here" );
}
Console.WriteLine("LAST STATEMENT");
}
}
Standard Exceptions
There are two types of exceptions: exceptions generated by an executing program and exceptions generated by the common language runtime. System.Exception is the base class for all exceptions in C#. Several exception classes inherit from this class including ApplicationException and SystemException. These two classes form the basis for most other runtime exceptions. Other exceptions that derive directly from System.Exception include IOException, WebException etc.
The common language runtime throws SystemException. The ApplicationException is thrown by a user program rather than the runtime. The SystemException includes the ExecutionEngineException, StaclOverFlowException etc. It is not recommended that we catch SystemExceptions nor is it good programming practice to throw SystemExceptions in our applications.
System.OutOfMemoryException
System.NullReferenceException
System.InvalidCastException
System.ArrayTypeMismatchException
System.IndexOutOfRangeException
System.ArithmeticException
System.DevideByZeroException
System.OverFlowException
User-defined Exceptions
In C#, it is possible to create our own exception class. But Exception must be the ultimate base class for all exceptions in C#. So the user-defined exception classes must inherit from either Exception class or one of its standard derived classes.
//C#: Exception Handling: User defined exceptions
//Author: rajeshvs@msn.com
using System;
class MyException : Exception
{
public MyException(string str)
{
Console.WriteLine("User defined exception");
}
}
class MyClient
{
public static void Main()
{
try
{
throw new MyException("RAJESH");
}
catch(Exception e)
{
Console.WriteLine("Exception caught here" + e.ToString());
}
Console.WriteLine("LAST STATEMENT");
}
}
Design Guidelines
Exceptions should be used to communicate exceptional conditions. Don’t use them to communicate events that are expected, such as reaching the end of a file. If there’s a good predefined exception in the System namespace that describes the exception condition-one that will make sense to the users of the class-use that one rather than defining a new exception class, and put specific information in the message.
Finally, if code catches an exception that it isn’t going to handle, consider whether it should wrap that exception with additional information before re-throwing it.
| DISCLAIMER: The content provided in this article is not warranted or guaranteed by Developer Shed, Inc. The content provided is intended for entertainment and/or educational purposes in order to introduce to the reader key ideas, concepts, and/or product reviews. As such it is incumbent upon the reader to employ real-world tactics for security and implementation of best practices. We are not liable for any negative consequences that may result from implementing any information covered in our articles or tutorials. If this is a hardware review, it is not recommended to open and/or modify your hardware. |
More C# Articles
More By Rajesh V S
 developerWorks - FREE Tools!
|
Hold your calendar on January 30, 2008 for this free webcast on the new i5/OS. Rational's Enterprise Modernization products will be discussed at this webcast as they help to drive the application development environment for this new System i OS. <br />And learn how i5/OS will take you to the next step of efficient, resilient business processing. You will hear about the new i5/OS capabilities as it will be the most significant i5/OS release in years. If you cannot join the webcast on 1/30/08 you can still use this link to listen to the replay.<br />
FREE! Go There Now!
|
|
|
|
Download the IBM WebSphere Portal V6.1 beta code and learn more about the rich features and enhancements in IBM WebSphere Portal V6.1. WebSphere Portal provides a composite application or business mashup framework and the advanced tooling needed to build flexible, SOA-based solutions, and scalability to meet the needs of any size organization.
FREE! Go There Now!
|
|
|
|
Download a free trial version of IBM Rational Software Analyzer Developer Edition V7.0 to identify bug defects earlier in the software development cycle. Rational Software Analyzer is an extensible software development solution that reduces the expense of bug-fixes by enabling static analysis code reviews and bug identification very early in the development cycle.
FREE! Go There Now!
|
|
|
|
Visit IBM developerWorks to download a free trial version of WebSphere Extended Deployment Compute Grid, which lets you schedule, execute, and monitor batch jobs. Because online transaction processing and batch jobs execute simultaneously on the same server resources, you can avoid costly duplication of resources. Compute Grid supports job types of Java transactional batch, compute-intensive and a new type called "native execution", which enables non-Java workloads to run on distributed end points.
FREE! Go There Now!
|
|
|
|
This tutorial shows new users of IBM WebSphere Business Monitor Version 6.0.2 how to perform the "Hello World" equivalent for monitoring business process applications. It is intended to help you get familiar with the capabilities of the product.
FREE! Go There Now!
|
|
|
|
XML has become a common way of storing business data as flat files and many data server vendors including IBM have provided ways to store this data within relational database systems. Increasingly collections of XML files are accessed like databases using an xQuery and other XML standard mechanisms. Businesses find the need to combine the traditional tabular structured data with XML formatted data. In this webcast, you’ll learn about IBM’s WebSphere Federation Server technology, which provides users with the ability to integrate these two data formats.
FREE! Go There Now!
|
|
|
|
This whitepaper provides areas to consider when evaluating any software configuration management solution. It addresses how the IBM solutions (Rational ClearCase and Rational ClearQuest) meet the needs and requirements of both project leaders and developers to provide successful Software Change and Configuration Management.
FREE! Go There Now!
|
|
|
|
Whether you are creating new applications or modifying existing ones, managing integration of new components with traditional z/OS elements is a critical part of building and deploying modern applications. Listen to this webcast to see how IBM can help you optimize your development process using an IDE like Rational Developer for System z that integrates with management tools, such as ClearCase to manage your application development on mainframes.
FREE! Go There Now!
|
|
|
|
WebSphere Process Server delivers a unique integration framework that simplifies existing IT resources. Often, as IT assets grow to support business demand, so too does their complexity and manageability. In this webcast, we’ll discuss how WebSphere Process Server helps deliver an SOA infrastructure that provides a common model to orchestrate, mediate, connect, map, and execute the underlying IT functions. Discover how WebSphere Process Server simplifies integration of business processes by leveraging existing IT assets as reusable services without the complexities of traditional integration methodologies.
FREE! Go There Now!
|
|
|
|
Viper 2 brings a great value to developer communities including SQL, XML, PHP, Ruby, .NET and Java. You probably already know that DB2 Express-C is free for developers to develop, deploy and distribute. Viper 2 provides a variety of means that help move your application from the development stage to deployment more rapidly. This webcast shows how to best utilize the latest tools available for developing DB2 applications.
FREE! Go There Now!
|
|
|
|
All FREE IBM® developerWorks Tools!
|
/ 19 
