Custom Exception Handling in VB.NET

Exception

Exceptions are the occurrence of some condition that changes the normal flow of execution .

For example:

Your program 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 .

The Concept

The whole idea of having customized Exception Handling is centered around the fact that there needs to be a generic approach of catching and throwing Exceptions.

For implementing custom Exception Handling we need to derive the class CustomException from the system base class ApplicationException. In general, for customizing Exception Handling the following components are necessary:

1. A custom exception class which would host the exception thrown and can be thrown as a new exception.
2. A message class that would host all user - friendly Application messages that need to be displayed.

 Creating Custom Exception

VB.NET define your own custom exceptions to identify the occurrence of unexpected events in your code.exceptions are implemented in VB.Net as classes and objects.

1. Create a exception kind of class and inherit it from Exception class.

2. Override the Message property and ToString() method.

For example:

Module Module1

    Class NotEnoughBalanceException

        Inherits Exception

        Public Overrides ReadOnly Property Message() As String

            Get

                Return "Sorry! Not Engouh Balance"

            End Get

        End Property

    End Class

    Class Customer

        Private name As String

        Private balance As Integer

        Public Sub New(ByVal name As String, ByVal opamt As Integer)

            Me.name = name

            Me.balance = opamt

        End Sub

        Public Sub Deposit(ByVal amount As Integer)

            balance += amount

        End Sub

        Public Sub Withdraw(ByVal amount As Integer)

            If amount > balance Then

                Throw New NotEnoughBalanceException()

            End If

            balance -= amount

        End Sub

        Public Sub ShowBalance()

            Console.WriteLine("Balance of {0} is {1}", name, balance)

        End Sub

    End Class

    Class ExpTest

        Public Shared Sub Main()

            Dim c As New Customer("Amit", 5000)

            Try

                c.Deposit(4000)

                c.ShowBalance()

                c.Withdraw(20000)

                c.ShowBalance()

            Catch ex As NotEnoughBalanceException

                Console.WriteLine(ex.Message)

            End Try

        End Sub

    End Class

 End Module

 OUTPUT:
 

Conclusion:

Hope this article would have helped you in understanding custom exception handling in VB.NET.