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is and how you can figure out what a string can do。
Investigating the String Type
String is a class type； and thus a reference type。 String is a type that has methods and proper
ties。 Value types like Double and Integer have methods and properties； but String is the first
type you are encountering that is a class in its own right （Double and Integer are not actually
classes）。
To investigate a type； you can read the documentation； or you can use IntelliSense。 Reading
the documentation is not a bad idea； but it is the slowest and most cumbersome。 IntelliSense
is an IDE approach； in which a defined type’s methods and properties are presented to you in
an easy…to…prehend manner。
The first time you use IntelliSense； it can be nerve…racking； because it seems like the IDE
has a life of its own。 There is a convention on how to use IntelliSense； as illustrated in Figure 3…2。
I suggest that you take a few moments to experiment with it。 I also remend that you keep
IntelliSense active in Visual Basic Express。
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56 CH AP T E R 3 ■ L E A R N IN G AB OU T ST R I N G M A N I P U L AT IO N S
Figure 3…2。 Using IntelliSense on a String typed variable
IntelliSense works on only identified variables that have types。 In Figure 3…2； IntelliSense
worked because the IDE parsed the code and had the ability to read the metadata associated
with the type。 Metadata is data that describes your source code。 Whenever you define a class；
methods and properties are associated with it。 The method and property descriptions are
pieces of metadata that is displayed by IntelliSense。 One of the strengths of is that all
types have metadata。
The Basis of All Types： Object
By default； everything in is an object with a few basic properties and methods。 Four basic
methods are associated with every object：
o Equals（）： Verifies the equality of two objects （see Figure 3…3）。
o GetHashCode（）： Retrieves a unique number describing the object （see Figure 3…4）。 Two
objects with the same contents will return the same hash code。
o GetType（）： Retrieves the metadata associated with an object （see Figure 3…5）。 Allows the
program to play “Are you a 。 。 。 ？” to dynamically determine which methods and proper
ties a type has。 It is used by IntelliSense to display a list box。
o ToString（）： Converts the contents of the type into a string （see Figure 3…6）。 Note that the
default CLR ToString（） implementations work only for value types。
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CH AP T E R 3 ■ L E AR N IN G AB O U T ST R I N G M A N I PU L A TI O N S 57
Calling Equals（） asks if variable
a has a value of 2
Dim a As Integer = 2
If a。Equals（2） Then
Console。WriteLine（〃2 equals 2； as it should be〃）
End If
This code will always be
called because 2 equals 2
Figure 3…3。 Equals（） is used to verify the equality of two objects。
Don’t think of a； b； and c as values associated
with a variable。 Think of a； b； and c as having
contents associated with the variables。 The
contents of a and b match； the contents of c do
not match the contents of a and b。
Dim a As Integer = 2 The contents of a and b are
Dim b As Integer = 2 identical； thus； GetHashCode（）
Dim c As Integer = 3
returns the same number
If a。GetHashCode（） = b。GetHashCode（） Then
Console。WriteLine（〃2 equals 2； as it should be〃）
End If
If c。GetHashCode（） b。GetHashCode（） Then
Console。WriteLine（〃3 does not equal 2； as it should be〃）
End If
The contents of c and b are not
equal； so GetHashCode（） will
return two different numbers
Figure 3…4。 GetHashCode（） retrieves a number describing the object。
The four basic methods can be called on every variable that you declare。 You will use
ToString（） when debugging or inspecting the state of an object instance during runtime。
ToString（） returns a human…readable string that contains the state of the object instance。
You might use the GetType（） method occasionally； but your IDE and other tools will use
it all the time。 Using GetType（）； you have the ability to figure out the capabilities of a variable
during the execution of a program。 In technical terms； GetType（） returns the formal metadata
description of the type。
From reading the description of Equals（） and GetHashCode（）； you would get the impression
that these two functions serve the same purpose。 However； this is not the case。
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58 CH AP T E R 3 ■ L E A R N IN G AB OU T ST R I N G M A N I P U L AT IO N S
You know that a is a value type
（as explained in Chapter 1）。
However； a program does not By calling GetType（） and
know that it is a value type。 then IsValueType； the
program is dynamically
Dim a As Integer = 1 asking if a is a value type
If a。GetType（）。IsValueType = True Then
Console。WriteLine（〃a is a value type〃）
End If
This code will always be called
because a is always a value type
Figure 3…5。 GetType（） retrieves the metadata associated with an object。
Variable a contains the value
3 as a binary value Calling ToString（） will convert the
binary…based value into a
character…based value
Dim a As Integer = 3
Dim aAsAString As String = a。ToString（）
If aAsAString = 〃3〃 Then
Console。WriteLine（〃3 has been converted into a string〃）
End If
The = sign is another way “3” always equals “3”
to test if “3” equals “3” so this code runs
Figure 3…6。 ToString（） converts the contents of the type into a string。
Let’s say you’re moving and you’ve packed two boxes containing kitchen items。 Both boxes
contain five red dishes； three silver forks； two copper knives； and two wineglasses。 If you pare
the boxes； both Equals（） and GetHashCode（） will return equality； indicating the boxes contain
the same number and color of items。 It is important to understand that even though the two
boxes are unique instances containing unique articles； their contents are identical。 When you
pare object instances using Equals（） or GetHashCode（）； you are paring the metadata
and value attributes； not the unique instances。
Now imagine the situation where one of the boxes has wineglasses from IKEA and the other
has wineglasses from Pier 1。 If you use the Equals（） method to pare the boxes； it will return
False； because the box content details ar