Sometimes errors or exceptional conditions prohibit a program from continuing its current activity. A classic example is division by zero:
Dim x As Integer = 0 Dim y As Integer = 1 \ x
When the process hits the line containing the integer division, an exception occurs. An exception is any occurrence that is not considered part of normal, expected program flow. The runtime detects, or catches, this exception and takes appropriate action, generally resulting in termination of the offending program. Figure 2-3 shows the message box that is displayed when this code is run within the Visual Studio .NET IDE.
Figure 2-3. A divide-by-zero exception
Visual Basic .NET programs can and should be written to catch
exceptions themselves. This is done by wrapping potentially dangerous
Example 2-9 shows how to catch the divide-by-zero
Example 2-9. Catching an exception
Try Dim x As Integer = 0 Dim y As Integer = 1 \ x Catch e As Exception Console.WriteLine(e.Message) End Try
When the program attempts the division by zero, an exception occurs,
and program execution jumps to the first statement in the
Catch block. The
statement declares a variable of type Exception that receives
information about the exception that occurred. This information can
then be used within the
Catch block to record or report the exception, or to take corrective action. ...