Tuesday, June 08, 2010

Working with Strings in .NET using VB.NET

.NET Framework library provides classes to work with strings and these classes are common to all .NET language including C# and VB.NET. In this tutorial, I will discuss how to use these classes to work with strings using VB.NET.

Comparing Strings.

The Compare method compares two strings and returns an integer value. The return value of Compare method can be less than zero, greater than zero or equals to zero.

Value Meaning.

Less than zero When first string is less than second.
Zero When both strings are equal.
Greater than zero When first string is greater than zero.

The following code compares two strings and return results on the System console.

' Comparing two strings
Dim str1 As String = "ppp"
Dim str2 As String = "ccc"
Dim res As Int16 = String.Compare(str1, str2)
Console.WriteLine("First result:" + res.ToString())
str2 = "ttt"
res = String.Compare(str1, str2)
Console.WriteLine("Second result:" + res.ToString())
str1 = "ttt"
res = String.Compare(str1, str2)
Console.WriteLine("Third result:" + res.ToString())

The CompareTo method is an instance method. It compares a value (either a string or on object) with a string instance. Return values of this method are same as the Compare method. The following source code compares two strings.

' CompareTo Method
Dim str As String = "kkk"

Copy and Concatenating Strings.

The Concat method adds strings (or objects) and returns a new string. Using Concat method, you can add two strings, two objects and one string and one object or more combinations of these two.

The following source code concatenate two strings.

Dim str1 As String = "ppp"
Dim str2 As String = "ccc"
Dim strRes As String = String.Concat(str1, str2)

The following source code concatenates one string and one object.

Dim obj As Object = 12
strRes = String.Concat(str1, obj)

The Copy method copies contents of a string to another. The Copy method takes a string as input and returns another string with the same contents as the input string. For example, the following code copies str1 to strRes.

strRes = String.Copy(str1)
Console.WriteLine("Copy result :" + strRes)

The CopyTo method copies a specified number of characters from a specified position in this instance to a specified position in an array of characters. For example, the following example copies contents of str1 to an array of characters. You can also specify the starting character of a string and number of characters you want to copy to the array.

Dim str1 As String = "pp"
Dim chrs(2) As Char
str1.CopyTo(0, chrs, 0, 2)
Console.WriteLine(chrs(0) + chrs(1))

The Clone method returns a new copy of a string in form of object. The following code creates a clone of str1.

Dim str1 As String = "ppp"
Dim objClone As Object = str1.Clone()
Console.WriteLine("Clone :" + objClone.ToString())

The Join method is useful when you need to insert a separator (String) between each element of a string array, yielding a single concatenated string. For example, the following sample inserts a comma and space (", ") between each element of an array of strings.

Dim str1 As String = "ppp"
Dim str2 As String = "ccc"
Dim str3 As String = "kkk"
Dim allStr() As String = New String() {str1, str2, str3}
Dim strRes As String = String.Join(", ", allStr)
Console.WriteLine("Join Results: " + strRes)

Adding, Removing and Replacing Strings.

The Insert method inserts a specified string at a specified index position in an instance. For example, the following source code inserts "bbb" after second character in str1 and the result string is "pbbbpp".

Dim str1 As String = "ppp"
Dim strRes As String = str1.Insert(2, "bbb")

The Remove method deletes a specified number of characters from a specified position in a string. This method returns result as a string. For example, the following code removes three characters from index 3.

Dim s As String = "123abc000"
Console.WriteLine(s.Remove(3, 3))

The Replace method replaces all occurrences of a specified character in a string. For example, the following source code replaces all p character instances of str1 with character l and returns string "lll".

Dim str1 As String = "ppp"
Dim repStr As String = str1.Replace("p", "l")
Console.WriteLine("Replaced string:" + repStr.ToString())

The Split method separates strings by a specified set of characters and places these strings into an array of strings. For example, the following source code splits strArray based on ',' and stores all separated strings in an array.

Dim str1 As String = "ppp"
Dim str2 As String = "ccc"
Dim str3 As String = "kkk"
Dim strAll3 As String = str1 + ", " + str2 + ", " + str3
Dim strArray() As String = strAll3.Split(",")

Uppercase and Lowercase.

The ToUpper and ToLower methods convert a string in uppercase and lowercase respectively. These methods are easy to use. The following code shows how to use ToUppler and ToLower methods.

Dim aStr As String = "adgas"
Dim bStr As String = "ABNMDWER"
Dim strRes As String = aStr.ToUpper()
Console.WriteLine("Uppercase:" + strRes.ToString())
strRes = bStr.ToLower()
Console.WriteLine("Lowercase:" + strRes.ToString())

Formatting Strings.

You can use the Format method to create formatted strings and concatenate multiple strings representing multiple objects. The Format method automatically converts any passed object into a string.

For example, the following code uses integer, floating number and string values and format them into a string using the Format method.

Listing 1. Using Format method to format a string.

Dim val As Int16 = 7
Dim name As String = "Mr. John"
Dim num As Double = 45.06F
Dim str As String = String.Format("Days Left : {0}. Current DataTime: {1:u}. \n String: {2}, Float: {3}", val, DateTime.Now, name, num)

Trimming and Removing Characters from Strings.

The String class provides Trim, TrimStart and TrimEnd methods to trim strings. The Trim method removes white spaces from the beginning and end of a string. The TrimEnd method removes characters specified in an array of characters from the end of a string and TrimStart method removes characters specified in an array of characaters from the beginning of a string.

You can also use the Remove method to remove characters from a string. The Listing 2 code shows how to use these methods.

Dim str As String = " C# "
Console.WriteLine("Hello{0}World!", str)
Dim trStr As String = str.Trim()
Console.WriteLine("Hello{0}World!", trStr)
str = "Hello World!"
Dim chArr() As Char = {"e", "H", "l", "o", " "}
trStr = str.TrimStart(chArr)
str = "Hello World!"
Dim chArr1() As Char = {"e", "H", "l", "o", " "}
trStr = str.TrimEnd(chArr1)
Dim MyString As String = "Hello Delta World!"
Console.WriteLine(MyString.Remove(5, 10))

Padding Strings.

The PadLeft and PadRight methods can be used to pad strings. The PadLeft method right-aligns and pads a string so that its rightmost character is the specified distance from the beginning of the string. The PadRight method left-aligns and pads a string so that its rightmost character is a specified distance from the end of the string. These methods return new String objects that can either be padded with empty spaces or with custom characters. Listign 3 shows how to use these methods.

Listing 3. Using padding methods.

Dim str1 As String = "My String"
Console.WriteLine(str1.PadLeft(20, "-"))
Dim str2 As String = "My String"
Console.WriteLine(str2.PadRight(20, "-"))

The output of Listing 3 is shown in Number 2


----------My String
My String----------

Using StringBuilder Class.

The StringBuilder class represents a mutable string of characters. It's called mutable because it can be modified once it has been created by using Append, Insert, Remove, and Replace methods.

Note: When there are multiple concatenation operations are involved with strings, for performance reasons it is recommended to use StringBuilder instead of String.

The StringBuilder class is defined in the System.Text namespace. Before you use the StringBuilder class make sure you add the following line in your application:

imports System.Text

Table 2 describes the StringBuilder class properties.

Property Description
Capacity Represents the maximum number of characters that can be contained in the memory allocated by the current instance.
Chars Represens the character at the specified position.
Length Represents the number of characters.
MaxCapacity Returns the maximum capacity.

Table 2. The StringBuilder class properties.

Table 3 describes the StringBuilder class methods.

Method Description
Append Appends a string at the end of this string.
AppendFormat Appends a formatted string.
EnsureCapaciry Ensures that the capacity of string is as specified value.
Inserts Inserts string at the specified position.
Remove Removes a range of characters from the string.
Replace Replaces all occurrences of a character from the string.

Table 3. The StringBuilder class methods.

Using StringBuilder properties and methods is pretty simple. Listing 4 uses StringBuilder class to append, insert, remove and replace characters of a string.

Listing 4. Using StringBuilder class to append, add, replace and remove characters.

Dim builder As StringBuilder = New StringBuilder("Hello C# World!", 20)
Dim cap As Int16 = builder.EnsureCapacity(55)
builder.Append(". This is a class test.")
builder.Insert(26, " String Builder")
builder.Remove(5, 9)
builder.Replace("!", "?")
Console.WriteLine("Length of string is:" + builder.Length.ToString())
Console.WriteLine("Capacity of string is:" + builder.Capacity.ToString())

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