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deferred execution code。 The advantage of deferred execution is that the code can contain
a state whenever it is executed。
Some Things for You to Do
The following are some things for you to do to start applying your budding knowledge of soft
ware engineering to improving the code base。
1。 Collection classes before Visual Basic 2005 allowed you to mix types。 With Visual Basic
2005 and later； the generics classes do not allow you to mix types。 Provide a
solution where you could mix types with Visual Basic 2005 and later collections。
2。 Create a list that contains the numbers 1 to 20。 Remove the numbers； 15； 10； and 3 to 7。
3。 Create a list with an object that is defined as follows：
Class MyType
Public Value as String
End Class
4。 Add ten elements to the list； and then sort the list alphabetically from A to Z。 Hint： look
at the method Sort（） and implement a custom Iparer（Of ）。 As part of this exercise；
you need to investigate and figure out how to use Iparer（Of ）。 My suggestion is to
search the MSDN and Code Project web sites。
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C H A P T E R 1 0
■ ■ ■
Learning About Persistence
Your programs will probably need to read and/or write data to some type of storage device。
That storage device might be a hard disk； USB drive； or even the network。 The key concept is
that you are taking information from memory and transferring it to some other location。 Later；
you will retrieve that information and use it to execute some task。
Taking data from memory and transferring it to another place is referred to as persistence。
Most examples of persistence involve creating an object； and then saving that object via a file
to the hard disk。 However； reading and writing an object is not just saving data to the hard disk；
even though that is often the result。 Reading and writing data to the hard disk is about reading
and writing to data streams。 This chapter focuses on the process of reading and writing data
to streams。
This chapter’s example is a set of applications for a lottery…prediction system。 You’ll see
how streams are generic concepts that can apply to files； the console； or even the network。
Throughout this book； the examples use console applications to test some code； and this
chapter’s example also includes console applications。 Although Visual Basic is typically used as
a GUI development tool； the point of using the console is to help you understand the Visual
Basic programming language。 One of the biggest criticisms of Visual Basic developers has been
that they can’t develop like real developers。 This book is intended for real developers who happen
to use Visual Basic。
Organizing the Lottery…Prediction System
Let’s say we want to predict the next set of lottery numbers。 We have a program that saves the
numbers drawn； and each week； we run a program that retrieves the drawn numbers and predicts
the next set of numbers。 Many will argue that lottery numbers are random and thus cannot be
predicted。 But that doesn’t mean that we can’t write a program to generate the probabilities；
and that usually entails knowing which numbers have been drawn previously。
The lottery…prediction example involves three applications： TextProcessor； which is used
to read a messed…up lottery number file that will be cleaned up； Binary2Text； which converts a
binary stream into text； and Text2Binary； which converts a text stream into binary。 Five projects
are defined for these applications：
o Binary2Text： A console program that is used to convert a binary lottery ticket stream into
a text stream。
o LottoLibrary： A class library that contains the definition of the Ticket type that repre
sents a lottery ticket in memory。
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250 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
o ReaderWriter： A class library that contains the infrastructure code for processing streams
and mand…line arguments。
o Text2Binary： A console program that is used to convert a text lottery ticket stream into a
binary stream。
o TextProcessor： A console application that will read and write a text file。 This application
will bee a prototype example of how to write a console…based application。 It
contains a reference to the ReaderWriter class library。
Piping Data Using a Console
Console applications are not very interactive； for the most part； they are keyboard…based appli
cations。 The main advantage of console applications is their ability to dynamically string data
stream manipulations together； a process called piping。
For the lottery…prediction example； TextProcessor is a console application that will be fed
data by a pipe and generate data using a pipe； as illustrated Figure 10…1。 A file feeds a pipe； which
feeds the console application that manipulates the data； which then feeds an outgoing pipe
that could be used to feed another console application。
Figure 10…1。 Pipeline approach to processing
TextProcessor will read a file of lottery numbers； clean them up （for example； by removing
empty lines of text）； and remove any duplicates。 The console program wil