Saturday, 14 September 2013

VB.Net Strings

In VB.Net you can use strings as array of characters, however, more common practice is to use the String keyword to declare a string variable. The string keyword is an alias for the System.String class.

Creating a String Object

You can create string object using one of the following methods:
  • By assigning a string literal to a String variable
  • By using a String class constructor
  • By using the string concatenation operator (+)
  • By retrieving a property or calling a method that returns a string
  • By calling a formatting method to convert a value or object to its string representation
The following example demonstrates this:
Module strings
   Sub Main()
      Dim fname, lname, fullname, greetings As String
      fname = "Rowan"
      lname = "Atkinson"
      fullname = fname + " " + lname
      Console.WriteLine("Full Name: {0}", fullname)

     'by using string constructor
      Dim letters As Char() = {"H", "e", "l", "l", "o"}
      greetings = New String(letters)
      Console.WriteLine("Greetings: {0}", greetings)

      'methods returning String
      Dim sarray() As String = {"Hello", "From", "Tutorials", "Point"}
      Dim message As String = String.Join(" ", sarray)
      Console.WriteLine("Message: {0}", message)

      'formatting method to convert a value 
      Dim waiting As DateTime = New DateTime(2012, 12, 12, 17, 58, 1)
      Dim chat As String = String.Format("Message sent at {0:t} on {0:D}", waiting)
      Console.WriteLine("Message: {0}", chat)
      Console.ReadLine()
   End Sub
End Module
When the above code is compiled and executed, it produces following result:
Full Name: Rowan Atkinson
Greetings: Hello
Message: Hello From Tutorials Point
Message: Message sent at 5:58 PM on Wednesday, December 12, 2012

Properties of the String Class

The String class has the following two properties:
S.NProperty Name & Description
1Chars
Gets the Char object at a specified position in the current String object.
2Length
Gets the number of characters in the current String object.

Methods of the String Class

The String class has numerous methods that help you in working with the string objects. The following table provides some of the most commonly used methods:
S.NMethod Name & Description
1Public Shared Function Compare ( strA As String, strB As String ) As Integer 
Compares two specified string objects and returns an integer that indicates their relative position in the sort order.
2Public Shared Function Compare ( strA As String, strB As String, ignoreCase As Boolean ) As Integer 
Compares two specified string objects and returns an integer that indicates their relative position in the sort order. However, it ignores case if the Boolean parameter is true.
3Public Shared Function Concat ( str0 As String, str1 As String ) As String 
Concatenates two string objects.
4Public Shared Function Concat ( str0 As String, str1 As String, str2 As String ) As String 
Concatenates three string objects.
5Public Shared Function Concat ( str0 As String, str1 As String, str2 As String, str3 As String ) As String 
Concatenates four string objects.
6Public Function Contains ( value As String ) As Boolean 
Returns a value indicating whether the specified string object occurs within this string.
7Public Shared Function Copy ( str As String ) As String 
Creates a new String object with the same value as the specified string.
8pPublic Sub CopyTo ( sourceIndex As Integer, destination As Char(), destinationIndex As Integer, count As Integer ) 
Copies a specified number of characters from a specified position of the string object to a specified position in an array of Unicode characters.
9Public Function EndsWith ( value As String ) As Boolean 
Determines whether the end of the string object matches the specified string.
10Public Function Equals ( value As String ) As Boolean 
Determines whether the current string object and the specified string object have the same value.
11Public Shared Function Equals ( a As String, b As String ) As Boolean 
Determines whether two specified string objects have the same value.
12Public Shared Function Format ( format As String, arg0 As Object ) As String 
Replaces one or more format items in a specified string with the string representation of a specified object.
13Public Function IndexOf ( value As Char ) As Integer 
Returns the zero-based index of the first occurrence of the specified Unicode character in the current string.
14Public Function IndexOf ( value As String ) As Integer 
Returns the zero-based index of the first occurrence of the specified string in this instance.
15Public Function IndexOf ( value As Char, startIndex As Integer ) As Integer 
Returns the zero-based index of the first occurrence of the specified Unicode character in this string, starting search at the specified character position.
16Public Function IndexOf ( value As String, startIndex As Integer ) As Integer 
Returns the zero-based index of the first occurrence of the specified string in this instance, starting search at the specified character position.
17Public Function IndexOfAny ( anyOf As Char() ) As Integer 
Returns the zero-based index of the first occurrence in this instance of any character in a specified array of Unicode characters.
18Public Function IndexOfAny ( anyOf As Char(), startIndex As Integer ) As Integer 
Returns the zero-based index of the first occurrence in this instance of any character in a specified array of Unicode characters, starting search at the specified character position.
19Public Function Insert ( startIndex As Integer, value As String ) As String 
Returns a new string in which a specified string is inserted at a specified index position in the current string object.
20Public Shared Function IsNullOrEmpty ( value As String ) As Boolean 
Indicates whether the specified string is null or an Empty string.
21Public Shared Function Join ( separator As String, ParamArray value As String() ) As String 
Concatenates all the elements of a string array, using the specified separator between each element.
22Public Shared Function Join ( separator As String, value As String(), startIndex As Integer, count As Integer ) As String 
Concatenates the specified elements of a string array, using the specified separator between each element.
23Public Function LastIndexOf ( value As Char ) As Integer 
Returns the zero-based index position of the last occurrence of the specified Unicode character within the current string object.
24Public Function LastIndexOf ( value As String ) As Integer 
Returns the zero-based index position of the last occurrence of a specified string within the current string object.
25Public Function Remove ( startIndex As Integer ) As String 
Removes all the characters in the current instance, beginning at a specified position and continuing through the last position, and returns the string.
26Public Function Remove ( startIndex As Integer, count As Integer ) As String 
Removes the specified number of characters in the current string beginning at a specified position and returns the string.
27Public Function Replace ( oldChar As Char, newChar As Char ) As String 
Replaces all occurrences of a specified Unicode character in the current string object with the specified Unicode character and returns the new string.
28Public Function Replace ( oldValue As String, newValue As String ) As String 
Replaces all occurrences of a specified string in the current string object with the specified string and returns the new string.
29Public Function Split ( ParamArray separator As Char() ) As String() 
Returns a string array that contains the substrings in the current string object, delimited by elements of a specified Unicode character array.
30Public Function Split ( separator As Char(), count As Integer ) As String() 
Returns a string array that contains the substrings in the current string object, delimited by elements of a specified Unicode character array. The int parameter specifies the maximum number of substrings to return.
31Public Function StartsWith ( value As String ) As Boolean 
Determines whether the beginning of this string instance matches the specified string.
32Public Function ToCharArray As Char()
Returns a Unicode character array with all the characters in the current string object.
33Public Function ToCharArray ( startIndex As Integer, length As Integer ) As Char() 
Returns a Unicode character array with all the characters in the current string object, starting from the specified index and up to the specified length.
34Public Function ToLower As String
Returns a copy of this string converted to lowercase.
35Public Function ToUpper As String
Returns a copy of this string converted to uppercase.
36Public Function Trim As String
Removes all leading and trailing white-space characters from the current String object.
The above list of methods is not exhaustive, please visit MSDN library for the complete list of methods and String class constructors.

Examples:

The following example demonstrates some of the methods mentioned above:
Comparing Strings:
#include <include.h>
Module strings
   Sub Main()
      Dim str1, str2 As String
      str1 = "This is test"
      str2 = "This is text"
      If (String.Compare(str1, str2) = 0) Then
          Console.WriteLine(str1 + " and " + str2 +
                            " are equal.")
      Else
          Console.WriteLine(str1 + " and " + str2 +
                            " are not equal.")
      End If
      Console.ReadLine()
   End Sub
End Module
When the above code is compiled and executed, it produces following result:
This is test and This is text are not equal.
String Contains String:
Module strings
   Sub Main()
      Dim str1 As String
      str1 = "This is test"
      If (str1.Contains("test")) Then
          Console.WriteLine("The sequence 'test' was found.")
      End If
      Console.ReadLine()
   End Sub
End Module
When the above code is compiled and executed, it produces following result:
The sequence 'test' was found.
Getting a Substring:
Module strings
   Sub Main()
      Dim str As String
      str = "Last night I dreamt of San Pedro"
      Console.WriteLine(str)
      Dim substr As String = str.Substring(23)
      Console.WriteLine(substr)
      Console.ReadLine()
   End Sub
End Module
When the above code is compiled and executed, it produces following result:
Last night I dreamt of San Pedro
San Pedro.
Joining Strings:
Module strings
   Sub Main()
      Dim strarray As String() = {"Down the way where the nights are gay",
                          "And the sun shines daily on the mountain top",
                           "I took a trip on a sailing ship",
                          "And when I reached Jamaica",
                          "I made a stop"}
      Dim str As String = String.Join(vbCrLf, strarray)
      Console.WriteLine(str)
      Console.ReadLine()
   End Sub
End Module
When the above code is compiled and executed, it produces following result:
Down the way where the nights are gay
And the sun shines daily on the mountain top
I took a trip on a sailing ship
And when I reached Jamaica
I made a stop
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