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w0051977
w0051977

Reputation: 15817

Polymorphism and Enums

Say I have a class structure like this:

 Public Class Student
    Public Enum Days
        Monday
        Tuesday
        Wednesday
        Thursday
    End Enum

    Public _Day As Days

    Public Shared Function Factory(ByVal StudentType As String, ByVal day As Days) As Student
        If StudentType = "PostGraduate" Then
            Return New PostGraduate(day)
        Else
            Return New Undergraduate(day)
        End If
    End Function    
 End Class

 Public Class PostGraduate
    Inherits Student

    Public Sub New(ByVal day As Days)    
    End Sub    
 End Class

 Public Class Undergraduate
    Inherits Student

    Public Sub New(ByVal day As Days)
        _Day = day
    End Sub
 End Class

Only the undergraduate class uses the enum, however the Enum has to be declared in the superclass (Student) because the factory method requires a Day to be passed to it. Is there a way I can put the Enum in the Undergraduate class? Unfortunately you cannot inherit from enums.

Upvotes: 0

Views: 100

Answers (1)

Tallmaris
Tallmaris

Reputation: 7590

If PostGraduate does not need to use Days, then take out the constructor Days parameter but initialise Days to a default value.

This brings another very important point: use a default 0 value for your Enums, something like Unknown, NotSet or anything. Enum are just kind-of glorified ints, if you don't initialise them they start at 0, which in your case means Days.Monday... that is not what you want.

You should also make your _Day property as public get but protected set (sorry I don't remember the VB keyword, basically it can only be set by itself and derived classes).

Upvotes: 1

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