Exceptions are the occurrence of some condition that changes the normal flow of execution . For ex: you programme run out of memory , file does not exist in the given path , network connections are dropped etc. More specifically for better understanding , we can say it as Runtime Errors .

In .NET languages , Structured Exceptions handling is a fundamental part of Common Language Runtime .

All exceptions in the Common Language Runtime are derived from a single base class , also you can create your own custom Exception classes. You can create an Exception class that inherits from Exception class .

You can handle Exceptions using Try..Catch statement .

Try
code
exit from Try
Catch [Exception [As Type]]
code - if the exception occurred this code will execute
exit from Catch

Finally

The code in the finally block will execute even if there is no Exceptions. That means if you write a finally block , the code should execute after the execution of try block or catch block.

Try
code
exit from Try
Catch [Exception [As Type]]
code - if the exception occurred this code will execute
exit Catch
Finally
code - this code should execute , if exception occurred or not

From the following VB.NET code , you can understand how to use try..catch statements. Here we are going to divide a number by zero .

VB.NET Source Code

Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button1.Click
Try
Dim i As Integer
Dim resultValue As Integer
i = 100
resultValue = i / 0
MsgBox("The result is " & resultValue)
Catch ex As Exception
MsgBox("Exception catch here ..")
Finally
MsgBox("Finally block executed ")
End Try
End Sub
End Class

When you execute this program you will "Exception catch here .." first and then "Finally block executed " . That is when you execute this code , an exception happen and it will go to catch block and then it will go to finally block.