Exceptions - Part I - Overview

Overview
An exception is an event which occurs during the execution of code which disrupts the normal flow due to the event.  When an error (exception) occurs within a method an exception object is createdwhich contains the details of the error.  After the exception is created - the runtime tries to find something to handle it.  The process of how the runtime handles the exception involves unwiding the stack, looks for a method that can handle the exception, or if it cannot then terminate the process and display the error to the user.

Handling the Exception
The exception will get handled - if you don't handle it.  This means your user will see the message - generally highly undesireable.  You should handle the exception by using a try, catch, finally block.

try
{
}
catch
{
}
finally
{
}
 

The tey-catch-exception block will only handle exceptions thrown in the "try" area.  This means you must be careful to not throw exceptions in the "catch" or "finally" blocks.


Handling Specific Exceptions
There are many occasions in which you want to handle the specific exception.  Imaging having a file-based or zero-based exception.  You could handle it gracefully rather than let the exception bubble up to the user.  An example would be to handle some of the following mathematical exceptions:

- Divide by Zero  (DivideByZeroException)
- Overflow  (OverflowException)
- Arithmetic (ArithmeticException)
- (to name a few)

try
{
}
catch(DivideByZeroException ex)
{
       handle the exception here
}
finally
{
}
 

Handling More Than 1 Exception
You can add additional catch blocks.  Just be careful that the exception handling will be done with the first catch block that meets the exception type.

try
{
}
catch(DivideByZeroException ex1)
{       handle this exception
}
catch(Exception ex2)
{
       handle all other exceptions
}
finally
{
}

 

Finally
The finally block is always executed, even if an exception is thrown.  Use this to close any open files, close streams, or release resources. The finally block is optional.