在父类型变量中使用子实例的Vb.net

Class Animal
    Public Overridable Sub MakeSound()
        Console.WriteLine("The animal makes a sound.")
    End Sub
End Class

Class Dog
    Inherits Animal
    Public Overrides Sub MakeSound()
        Console.WriteLine("The dog barks.")
    End Sub
End Class

Class Cat
    Inherits Animal
    Public Overrides Sub MakeSound()
        Console.WriteLine("The cat meows.")
    End Sub
End Class

Sub Main()
    Dim animal As Animal

    animal = New Dog()
    animal.MakeSound() ' 输出：The dog barks.

    animal = New Cat()
    animal.MakeSound() ' 输出：The cat meows.
End Sub