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 . It has a number of advantages over the On Error statements provided in previous versions of Visual Basic . 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 .

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