The API is vast； but you will not need to use all of the API all the time。 What you need to be aware of are the general classes of the API。 What part of the API is used to read and write streams？ What part of the API is used to create GUI elements？ This means you are not ever going to be an expert on all parts of the API； although you might be an expert Visual Basic programmer and understand the general concepts。 When I understand a domain quite well； I develop using a bottom…up approach。 This works because I know which interface and implementation need to talk to which other interface and implementation。 When I don’t understand a domain fully； I develop using a top…down approach。 Using a top…down approach； I can figure out what the pieces are in a simplified manner。 I create my echo program； which gives a plete round…trip without getting bogged down in the details of the API。 Think of a bunch of guys putting together a barbecue grill。 They might look at the instructions； but more likely； they will look at the parts and try to mentally fit the pieces together。 They might even put a couple of pieces together to get an idea of what each piece does and how the overall grill should appear。 Once they bee confident of their prototype； they build the real thing； which hopefully resembles a barbecue grill。 When you use this approach； what you are doing is building a mockup； proof of concept； or prototype。 Maybe two or three team members might help develop this prototype； but the fact that your code needs to be declared as a prototype is extremely important。 …………………………………………………………Page 279…………………………………………………………… CH A PT E R 1 0 ■ L E A R N I N G A B O U T P E R S IS T E N CE 257 Visual Basic Express and the Visual Studio products help you in that they allow you to embed task markers。 Go back to the source code example where LottoTicketProcessor was illustrated and look at the ment： " TODO： Finish implementing the class Notice TODO is in all capital letters。 That type of ment is special。 It is called a task and is tracked by Visual Basic Express in the Task List window。 To open ments in the Task List window； select View Other Windows Task List； and then select ments from the drop…down list at the top of the window。 This allows a team of developers to add markers throughout the entire code base； indicating what is done and not done。 That way； you will not forget to do certain tasks。 Some other identifiers that you can use are HACK to identify some code that is not correct； but hacked in so that it works； and UNDONE。 If you happen to be using a Visual Studio edition other than Express； you can define your own ment identifiers。 For more information； see the MSDN article “Visual Studio How to： Create Custom ment Tokens” （http：//msdn2。microsoft。/en…US/library/ekwz6akh（VS。80）。aspx）。 Implementing Stream Reading and Writing Finishing the stream reading and writing means looking at the possible arguments that can be given； and then implementing the code to process the arguments。 Here is the plete source code for ReaderWriter。Bootstrap： #Const DEBUG_OUTPUT = True Imports System。IO Public Module Bootstrap Public Sub DisplayHelp（） Console。WriteLine（〃You need help？ Right now？〃） End Sub Public Sub Start（ByVal args As String（）； ByVal processor As IProcessor） #If DEBUG_OUTPUT Then Console。WriteLine（〃Argument count（〃 & args。Length & 〃）〃） For Each argument As String In args Console。WriteLine（〃Argument （〃 & argument & 〃）〃） Next #End If Dim reader As TextReader = Nothing Dim writer As TextWriter = Nothing If args。Length = 0 Then reader = Console。In writer = Console。Out ElseIf args。Length = 1 Then If args（0） = 〃…help〃 Then Bootstrap。DisplayHelp（） Return End If …………………………………………………………Page 280…………………………………………………………… 258 CH AP T E R 1 0 ■ L E A R N I N G A B OU T P E R S IS TE N CE reader = File。OpenText（args（0）） writer = Console。Out ElseIf args。Length = 2 Then If args（0） 〃…out〃 Then Bootstrap。DisplayHelp（） Return End If reader = Console。In writer = File。CreateText（args（1）） ElseIf args。Length = 3 Then If args（0） 〃…out〃 Then Bootstrap。DisplayHelp（） Return End If reader = File。OpenText（args（2）） writer = File。CreateText（args（1）） Else Bootstrap。DisplayHelp（） Return End If writer。Write（processor。Process（reader。ReadToEnd）） End Sub End Module In the code； before the first If block； the variables reader and writer are assigned to the value Nothing； indicating that there is a reader and there is writer； but we don’t know whether they will reference streams or files。 Then the If blocks go through the different binations and variations of the mand…line arguments （see Table 10…1）。 The code follows a truth table app