VB'NET Inheritance and Interfaces

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VB.NET Inheritance and Interfaces

• Richard Vantrease

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Introduction

• Inheritance a class can based on an existing
  class, inheriting its interface and functionality
  from the base class.
• Interface the public methods, properties,
  events and fields

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Diagramming Inheritance
Diagram created with Poseidon for UML Community
Edition
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Base and Sub Classes

• A base class is a class that another class
  inherits its methods, properties, attributes and
  events from.
• A sub class is a class that inherits methods,
  properties, attributes and events from.

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Multi-Level Inheritance

• Inheritance is able to go multiple levels.
• Sometimes referred to as an inheritance chain.
• Person
• Employee
• Exempt
• Non-Exempt
• Customer

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Reference Keywords

• Me current object instance
• MyBase Immediate parent or base class. There
  is no built in way to navigate beyond immediate
  parent class.
• MyClass Object reference to current class.

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Overload

• Different method signature, different
  functionality.
• Base Class
• Sub Class
• Uses overloads keyword
• Public Overloads Property FName

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Override

• Same method signature, different functionality.
• Base Class
• Uses overridable keyword
• Public Overridable Property FName
• Sub Class
• Uses overrides keyword
• Public Overrides Property FName

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Virtual Methods Reference
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Shadow

• Allows methods in the base class that were not
  declared as overridable to be replaced in the sub
  class.

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Abstract Base Class

• A class that can only act as a base class.
• Provides no implementation, only interface
  definitions.
• Class uses the MustInherit keyword.
• Public MustInherit Class Person
• Method uses the MustOverride keyword
• Public MustOverride Sub Method1()

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Interfaces

• Default Interface
• Secondary Interfaces
• Implementation Re-Use

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Default Interface

• Used when class is used as the type in both the
  declaration and instantiation statements.
• Dim MyObject as Class1
• MyObject New Class1

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Secondary Interface

• Interface is created much like a class.
• Public Interface ISecInterface
• ReadOnly Property Count () As Integer
• Sub DoSomething ()
• End Interface
• Implemented with the implements keyword.
• Subs and Properties must use the implements
  keyword (i.e. Implements ISecInterface.Count)