`Replace`

This VB.NET function changes the contents of a String. It makes all instances of one substring become another substring.

It is important to know some of this Function's details. Replace() cannot handle patterns or regular expressions. It can cause performance problems.

First example

Here we call Replace. Its parameters can be literal strings or dynamic ones determined at runtime. We replace the first parameter with the second parameter.

Argument 1 The first argument we pass to the Replace Function is the substring we want to change to something else.

Argument 2 This is the string we want to have in the result—the replacement value. This may be found in the result of Replace.

Module Module1
    Sub Main()

        ' Replace substring with another substring.
        Dim value1 As String = "abcdef"
        Dim value2 As String = value1.Replace("abc", "hi")
        Console.WriteLine(value1)
        Console.WriteLine(value2)

    End Sub
End Moduleabcdef
hidef

Every instance

Replace() will internally loop through the entire source string. It replaces all occurrences of the substring you want to replace.

Tip This behavior is useful when dealing with common string replacements in programs.

But If you do not understand this behavior you may end up writing inefficient code that has unneeded loops.

Here The string containing the characters "Net" is replaced with the characters "Bottle." These substrings are case-sensitive.

Module Module1
    Sub Main()
        ' Assign string to literal constant.
        Dim value1 As String = "Dot Net Perls is about Dot Net."
        Console.WriteLine(value1)

        ' Replace every instance of the string.
        Dim value2 As String = value1.Replace("Net", "Bottle")
        Console.WriteLine(value2)
    End Sub
End ModuleDot Net Perls is about Dot Net.
Dot Bottle Perls is about Dot Bottle.

`Remove` all substrings

We can use Replace() to remove all substrings from a string. A new copy of the string, with all matching substrings removed, is returned.

Important A zero-length string (the empty string literal) is still a string, so we can replace substrings with it.

Detail We can use an empty string literal or the Nothing literal to indicate an empty string.

Module Module1

    Sub Main()
        Dim value As String = "cat Remove dog Remove bird"
        ' We can use Replace to remove all instances of a substring.
        Dim result As String = value.Replace("Remove", "")
        Console.WriteLine("BEFORE: " + value)
        Console.WriteLine("AFTER: " + result)
    End Sub

End ModuleBEFORE: cat Remove dog Remove bird
AFTER: cat  dog  bird

`StringBuilder`

This class has a Replace() that functions the same way as the String method. It has parameters that indicate the before and after substrings.

However The StringBuilder class implements optimizations that can improve memory usage and speed when doing many replacements.

Imports System.Text

Module Module1
    Sub Main()
        ' Create new StringBuilder and initialize it.
        Dim builder As New StringBuilder("This is an example.")
        Console.WriteLine(builder)

        ' Replace string in StringBuilder.
        builder.Replace("This", "Here")
        Console.WriteLine(builder)

        ' Insert into StringBuilder.
        builder.Insert(0, "Sentence: ")
        Console.WriteLine(builder)
    End Sub
End ModuleThis is an example.
Here is an example.
Sentence: Here is an example.

The Replace function on String will allocate an entire new string. It will replace all instances of the first parameter with the second parameter.

Replace

First example

Every instance

Remove all substrings

StringBuilder

`Replace`

`Remove` all substrings

`StringBuilder`