Exceptions are a way to handle errors or unexpected situations in a Visual Basic .NET program. You can throw an exception explicitly using the Throw statement. The syntax for throwing an exception is as follows:
Throw New Exception("Description of the error")
Here's an example that throws an exception when a user enters an incorrect password:
Dim password as String = "MyPassword"
Dim inputPassword as String = Console.ReadLine()
If inputPassword <> password Then
Throw New Exception("Incorrect Password. Please try again.")
EndIf
In this example, if the user enters an incorrect password, the Throw statement will be executed, and an exception with the message "Incorrect Password. Please try again" will be thrown. This exception will need to be handled by the calling code.
You may also create custom exception classes by creating a class that inherits from the Exception class.
Public Class CustomException
Inherits Exception
Public Sub New(message As String)
MyBase.New(message)
End Sub
Public Sub New(message As String, innerException As Exception)
MyBase.New(message, innerException)
End Sub
End Class
In this custom exception class, we have created two constructors that can set a message for the exception, as well as an inner exception.
To use this custom exception, we can simply create a new instance of it and throw it similar to the previous example:
Dim input as Integer = Console.ReadLine()
If input < 0 Then
Throw New CustomException("Number cannot be negative.")
EndIf
This will create a new instance of the CustomException class and throw it, with the message "Number cannot be negative".