Strategy in VB.NET

   1:      ' Strategy Design Pattern.

   2:      ' See description in //www.vb-net.com/ProgramTheory/Strategy.htm

   3:      Class MainApp

   4:          ' Entry point into console application.

   5:          Public Shared Sub Main()

   6:              Dim context As Context

   7:              ' Three contexts following different strategies

   8:              context = New Context(New ConcreteStrategyA())

   9:              context.ContextInterface()

  10:              context = New Context(New ConcreteStrategyB())

  11:              context.ContextInterface()

  12:              context = New Context(New ConcreteStrategyC())

  13:              context.ContextInterface()

  14:              ' Wait for user

  15:              Console.ReadKey()

  16:          End Sub

  17:      End Class

  18:   

  19:      ' The 'Strategy' abstract class

  20:      MustInherit Class Strategy

  21:          Public MustOverride Sub AlgorithmInterface()

  22:      End Class

  23:   

  24:      ' A 'ConcreteStrategy' class

  25:      Class ConcreteStrategyA

  26:          Inherits Strategy

  27:          Public Overrides Sub AlgorithmInterface()

  28:              Console.WriteLine("Called ConcreteStrategyA.AlgorithmInterface()")

  29:          End Sub

  30:      End Class

  31:   

  32:      ' A 'ConcreteStrategy' class

  33:      Class ConcreteStrategyB

  34:          Inherits Strategy

  35:          Public Overrides Sub AlgorithmInterface()

  36:              Console.WriteLine("Called ConcreteStrategyB.AlgorithmInterface()")

  37:          End Sub

  38:      End Class

  39:   

  40:      ' A 'ConcreteStrategy' class

  41:      Class ConcreteStrategyC

  42:          Inherits Strategy

  43:          Public Overrides Sub AlgorithmInterface()

  44:              Console.WriteLine("Called ConcreteStrategyC.AlgorithmInterface()")

  45:          End Sub

  46:      End Class

  47:   

  48:      ' The 'Context' class

  49:      Class Context

  50:          Private _strategy As Strategy

  51:          ' Constructor

  52:          Public Sub New(strategy As Strategy)

  53:              Me._strategy = strategy

  54:          End Sub

  55:          Public Sub ContextInterface()

  56:              _strategy.AlgorithmInterface()

  57:          End Sub

  58:      End Class