如何在VB.NET的派生类中禁止基类的属性或方法？

Question

Supose a base class

Public Class airplane

Private var_num_seats As Integer
Private var_num_engines As Integer

Protected Property num_seats As Integer
    Get
        Return var_num_seats
    End Get
    Set(ByVal param_num_seats As Integer)
        var_num_seats = param_num_seats
    End Set
End Property

Protected Friend Property num_engines As Integer
    Get
        Return var_num_engines

    End Get
    Set(ByVal param_num_engines As Integer)
        var_num_engines = param_num_engines
    End Set
End Property

Protected Friend Sub take_off()
    'Do take off tasks
End Sub

Protected Friend Sub start_engines()
    'start each engine
End Sub

End Class

And a child class

Public Class glider
Inherits airplane

Private var_towed As Boolean
Private var_glide_rate As Double

Public ReadOnly Property towed As Boolean
    Get
        Return var_towed
    End Get
End Property

Public ReadOnly Property glide_rate As Double
    Get
        Return var_glide_rate
    End Get
End Property

Public Sub to_glide()
    'do gliding
End Sub

End Class

Obviously, I don't wish that the class Glider has the method "start_engines" neither the property "num_engines". Otherwise, other child classes may have. How can I supress these property and method in child class, not just ignoring (if I can)?

Thanks!

Answer 1

You Cant!

Reason: Breaks object orientedness!!!!

Suppose you have:

public void ThisIsAMethod(Airplane plane)
{
    plane.start_engines();
}

Now you use it as such:

Airplane aPlane = new Glider();
ThisIsAMethod(aPlane);

Oh no, aPlane is really a glider, and hence you shouldn't be able to call it. However, it is an airplane and thus has the method.

Solution:

1. Form a true inheritence. A glider is not an airplane. Maybe you can have a base class for "FlyingMachine" or "WingedFlier" or something which they both extend.

2. Hackmode! In Glider:

   Protected Friend Sub start_engines() throw new NotSupportedException() End Sub

Answer 2

I suspect you're looking to use an interface.

http://msdn.microsoft.com/en-us/library/h9xt0sdd.aspx