Creating your own exception class

This lesson covers writing a custom exception class in VB.NET, with the aim of expressing kinds of error more specifically.

Inherits Exception creates a custom exception class from the standard one. Use it when you want an application-specific error — a failed input check, say — to have a name of its own.

In the sample code, a ValidationError class inherits Exception, and CheckAge raises it with Throw New ValidationError(...) when the age is below zero. Catch e As ValidationError then catches just that kind.

A common early stumble is sticking to the standard Exception and losing the ability to tell errors apart. A custom class lets the Catch side respond differently per kind of error.

In professional work, it is usual to define errors that matter to the business — validation failures, permission errors — as their own exception classes, which makes error handling far clearer.

📖 Reference code

Class ValidationError
    Inherits Exception
    Public Sub New(message As String)
        MyBase.New(message)
    End Sub
End Class

Function CheckAge(age As Integer) As Integer
    If age < 0 Then
        Throw New ValidationError("Age must be 0 or greater")
    End If
    Return age
End Function

Try
    CheckAge(-5)
Catch e As ValidationError
    Console.WriteLine("ValidationError: " & e.Message)
End Try

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run VB.NET directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).