Section 7.1. The System Namespace

7.1. The System Namespace

The System namespace contains classes for such wide-ranging features as:

• Data types

• Data-type conversions

• Events and event handlers

• Mathematics

• Program invocation

• Application-environment management

It is also the root for almost every other significant Microsoft-supplied .NET class and namespace.

7.1.1. The System.Convert Class

The System namespace defines a class called Convert, which implements various data conversion methods. One such method is ToBoolean, which includes the following usage variations:

     Overloads Public Shared Function ToBoolean(Boolean) As Boolean     Overloads Public Shared Function ToBoolean(Byte) As Boolean     Overloads Public Shared Function ToBoolean(Char) As Boolean     Overloads Public Shared Function ToBoolean(DateTime) As Boolean     Overloads Public Shared Function ToBoolean(Decimal) As Boolean     Overloads Public Shared Function ToBoolean(Double) As Boolean     Overloads Public Shared Function ToBoolean(Integer) As Boolean     Overloads Public Shared Function ToBoolean(Long) As Boolean     Overloads Public Shared Function ToBoolean(Object) As Boolean     Overloads Public Shared Function ToBoolean(SByte) As Boolean     Overloads Public Shared Function ToBoolean(Short) As Boolean     Overloads Public Shared Function ToBoolean(Single) As Boolean     Overloads Public Shared Function ToBoolean(String) As Boolean     Overloads Public Shared Function ToBoolean(UInt16) As Boolean     Overloads Public Shared Function ToBoolean(UInt32) As Boolean     Overloads Public Shared Function ToBoolean(UInt64) As Boolean 

As you can see, there are many ToBoolean functionseach one overloaded with a different argument signatureto take care of converting various data types to a Boolean.

Now, just for exercise, consider this block of code:

     Dim textVersion As String     Dim trueVersion As Boolean     textVersion = "false"     trueVersion = System.Convert.ToBoolean(textVersion)     MsgBox(trueVersion)   ' Displays "False" 

Because the System namespace is always available (or if we are programming outside of Visual Studio, we can import it using the Imports statement), we can omit the System qualifier and write:

     trueVersion = Convert.ToBoolean(textVersion) 

The built-in VB function CBool also performs this conversion.

The Convert class contains methods for converting data to the standard Visual Basic data types, as well as to other data types supported by the .NET Framework but not wrapped by Visual Basic. (New in 2005. Beginning in the 2005 release, Visual Basic now includes native implementations of all core .NET data types.) The most important of these methods are shown in Table 7-1.

Table 7-1. Members of the System.Convert class

Method	VB equivalent	Description
ToBoolean	CBool	Converts a value to Boolean
ToByte	CByte	Converts a value to an unsigned 8-bit integer Byte
ToChar	CChar	Converts a value to a single character Char
ToDateTime	CDate	Converts a value to date or time value DateTime (Date in Visual Basic)
ToDecimal	CDec	Converts a value to a floating point Decimal
ToDouble	CDbl	Converts a value to a floating point Double
ToInt16	CShort	Converts a value to a signed 16-bit integer Int16 (Short in Visual Basic)
ToInt32	CInt	Converts a value to a signed 32-bit integer Int32 (Integer in Visual Basic)
ToInt64	CLng	Converts a value to a signed 64-bit integer Int64 (Long in Visual Basic)
ToSByte	New in 2005: CSByte	Converts a value to a signed 8-bit integer SByte (New in 2005: SByte in Visual Basic)
ToSingle	CSng	Converts a value to a floating point Single
ToString	CStr	Converts a value to a character String
ToUInt16	New in 2005: CUShort	Converts a value to an unsigned 16-bit integer UInt16 (New in 2005: UShort in Visual Basic)
ToUInt32	New in 2005: CUInt	Converts a value to an unsigned 32-bit integer UInt32 (New in 2005: UInteger in Visual Basic)
ToUInt64	New in 2005: CULng	Converts a value to an unsigned 64-bit integer UInt64 (New in 2005: ULong in Visual Basic)

7.1.2. The System.Array Class

The System.Array class contains useful methods for dealing with arrays. For instance, it has a Sort method that sorts the elements of an array. The following block of code uses Array.Sort to order a list of Integer values.

     Public Sub SortArray(  )        ' ----- Simple array sorting example.        Dim counter As Integer        Dim dataToFix(  ) As Integer = {9, 8, 12, 4, 5}        ' ----- First, show the world the mixed-up mess.        Console.WriteLine("Unsorted:")        For counter = 0 To 4           Console.WriteLine(CStr(dataToFix(counter)))        Next counter        ' ----- Yeah! I don't have to Bubble sort by myself.        Array.Sort(dataToFix)        ' ----- Display the correct results.        Console.WriteLine("Sorted:")        For counter = 0 To 4           Console.WriteLine(dataToFix(counter))        Next counter     End Sub 

The output is:

     Unsorted:     9     8     12     4     5     Sorted:     4     5     8     9     12 

Some of the more important methods of the Array class are shown in Table 7-2.

Table 7-2. Some members of the System.Array class

Method	Description
BinarySearch	Searches a sorted one-dimensional array for a value
IndexOf	Returns the location of the first occurrence of a particular value in a one-dimensional array
LastIndexOf	Returns the location of the last occurrence of a particular value in a one-dimensional array
Reverse	Reverses the order of the elements in a one-dimensional array or a portion of a one-dimensional array
Sort	Sorts a one-dimensional array

New in 2005. Beginning with the 2.0 release of the .NET Framework, System.Array now includes features that support the new generics functionality, including a wrapper for read-only, type-specific arrays. For information on using generics, see Chapter 10.

7.1.3. The System.Math Class

The System.Math class includes a number of mathematical methods (such as trigonometric functions), as well as some more useful general numeric methods, such as Max and Min. For instance, to determine the maximum of two values, use:

     MsgBox("The maximum of 4 and 7 is " & Math.Max(4, 7)) 

Table 7-3 shows the members of the Math class.

Table 7-3. The members of the System.Math class

Topic	Description
Abs Method	Absolute value
Acos Method	Arccosine
Asin Method	Arcsine
Atan Method	Arctangent; returns the angle with the tangent that is a specified number
Atan2 Method	Arctangent; returns the angle with the tangent that is the quotient of two specified numbers
BigMul Method	Multiplies two large 32-bit integers, returning a 64-bit integer
Ceiling Method	Returns the smallest integer greater than or equal to the argument
Cos Method	Cosine
Cosh Method	Hyperbolic cosine
DivRem Method	Returns the modulus, that is, the remainder of a division operation
E Field	The natural number e
Exp Method	The natural number e raised to a power
Floor Method	Returns the largest integer less than or equal to the argument
IEEERemainder Method	Returns the remainder of a division operation using an IEEE-defined standard function
Log Method	Natural (base e) logarithm
Log10 Method	Common (base 10) logarithm
Max Method	Maximum of two values
Min Method	Minimum of two values
Pi Field	p, the ratio of the circumference of a circle to its diameter
Pow Method	Exponentiation function
Round Method	Rounds a given number to a specified number of decimal places
Sign Method	Determines the sign of a number
Sin Method	Sine
Sinh Method	Hyperbolic sine
Sqrt Method	Square root of a value
Tan Method	Tangent
Tanh Method	Hyperbolic tangent
Truncate Method	Returns the integral portion of a number

7.1.4. The System.String Class

The System.String class implements a set of string manipulation features, including methods for substring isolation, concatenation, replacement, padding, trimming, and so on.

The VB String data type is equivalent to the System.String class, so the methods of System.String apply directly to VB strings, as with the Insert method:

     Dim famousQuote As String = "To be to be"     MsgBox(famousQuote.Insert(6, "or not ")) 

This displays the message, "To be or not to be."

In .NET, strings are immutable. That is, they cannot be modified once they are created. All methods of the String class that make changes to strings actually create a new instance of a string that contains the changes.

Table 7-4 shows some significant members of the System.String class.

Table 7-4. Some members of the System.String class

Member	Description
Chars Property	Returns the character at a specific position
Compare Method	Compares two string objects
CompareTo Method	Compares a string with a designated object
Concat Method	Concatenates one or more strings
Contains Method	Indicates whether a string contains a certain substring
Copy Method	Creates a new copy of an existing string
CopyTo Method	Copies characters from a string into a character array
Empty Field	A read-only field that represents an empty string
EndsWith Method	Indicates whether the end of a string matches a specified string
Equals Method	Determines whether a string is equal to another string
Format Method	Returns a new string built from a patterned format of one or more data objects
IndexOf Method	Returns the position of the first occurrence of a substring within a string
IndexOfAny Method	Returns the position within a string of the first occurrence of any character from a given set of characters
Insert Method	Inserts a substring into a string
Join Method	Concatenates each element of a string array with a specific delimiter between each original string, and returns a new string with the result
LastIndexOf Method	Returns the position of the last occurrence of a substring within a string
LastIndexOfAny Method	Returns the position within a string of the last occurrence of any character from a given set of characters
Length Property	Returns the number of characters in a string
PadLeft Method	Right-aligns the characters in a string
PadRight Method	Left-aligns the characters in a string
Remove Method	Deletes a specified number of characters from a string starting at a specific position
Replace Method	Replaces all occurrences of a substring in a string with another substring
Split Method	Splits a delimited string into an array of strings
StartsWith Method	Indicates whether the beginning of a string matches a particular substring
Substring Method	Extracts a substring from a string by position
ToCharArray Method	Copies the characters of a string to a character array
ToLower Method	Converts a string to lowercase
ToUpper Method	Converts a string to uppercase
Trim Method	Removes all occurrences of a set of characters (usually whitespace characters) from the beginning and end of a string
TrimEnd Method	Removes all occurrences of a set of characters (usually whitespace characters) from the end of a string
TrimStart Method	Removes all occurrences of a set of characters (usually whitespace characters) from the beginning of a string