Abstraction (VB.Net and Access VBA Cross Reference Guide)

General Info: Abstract Class / Abstract Member

An abstract class member is a member that is specified in a class but not implemented. Classes that inherit from the class will have to implement the abstract member. Abstract members are a technique for ensuring a common interface with descendant classes. An abstract class is a class you cannot instantiate. A pure abstract class is a class with only abstract members.

Languages Focus

Abstraction is supported at various levels with each language. A language could enforce abstraction at the class level (either enforcing a no-instantiation rule or a only abstract members rule), and with class members (member methods and/or properties).

VB.Net:   MustInherit, MustOverride, Overrides VB.Net supports abstract class members and abstract classes using the MustInherit and MustOverride modifiers. An abstract class is indicated with a MustInherit modifier and is a class with one or more abstract members and you cannot instantiate an abstract class. However, you can have additional implemented methods and properties. An abstract member is either a method (implicitly virtual), property, indexer, or event in an abstract class. You can add abstract members ONLY to abstract classes using the MustOverride keyword. Then you override it in a descendant class with Overrides. Syntax Example: Public MustInherit Class Cyborg   Public MustOverride Sub Speak(ByVal pMessage As String) End Class Public Class Series600   Inherits Cyborg   Public Overrides Sub Speak(ByVal pMessage As String)     MessageBox.Show(pMessage)   End Sub End Class  VB.Net Abstraction (MustInherit, MustOverride, Overrides)

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