How to VB.NET String Null

In VB.NET, a string is an array of characters declared using the "string" keyword. String objects are immutable, signifying that their contents cannot be altered once they have been instantiated. This immutability ensures that string values remain consistent and prevents accidental modifications, providing stability and reliability in string manipulations and operations within VB.NET applications..

What is VB.NET null ?

A null value represents the absence of an object reference. In VB.NET, strings are reference types and can hold the null value, just like other reference types. In VB.NET, the keyword "Nothing" is used to denote null values. When declaring a string within a class, it is recommended not to initialize it to null. Instead, it is considered best practice to initialize it to the constant "String.Empty", which represents an empty string. This ensures clarity and consistency in handling string values, avoiding potential null reference errors and promoting code readability.

What is an Empty Strings ?

An empty string, represented by an instance of the System.String object, is a string that does not contain any characters. It is frequently utilized in programming to denote a blank or empty text field. In VB.NET, empty strings are initialized using double quotation marks with no characters between them, like "" or String.Empty. This allows for the explicit representation of an absence of textual content and aids in distinguishing between an empty string and a null value in string operations and comparisons.

Dim str As String = ""

What is a Null Strings ?

A null string does not point to a valid instance of the System.String object, and any attempt to invoke a method on a null string will result in a NullReferenceException.

Dim str As String = Nothing Dim i As Integer = str.Length

When run the above code it will throw NullReferenceException.

How to check null String in ?

VB.NET uses the keyword Nothing for null values.

Dim str As String = Nothing If str = Nothing Then MsgBox("String is Null") End If

In the above code we created a string Object and assigned Nothing and next we check the string is null or not.

IsNullOrEmpty method

The method IsNullOrEmpty is a convenient way to check whether a String is either Nothing or Empty. It is equivalent to the following code:

result = s Is Nothing OrElse s = String.Empty

Dim str As String = Nothing If String.IsNullOrEmpty(str) Then MsgBox("String is null") End If
Full Source VB.NET
Public Class Form1 Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim str As String = Nothing If str = Nothing Then MsgBox("String is null") Else MsgBox("String is not null") End If str = "notempty" If String.IsNullOrEmpty(str) Then MsgBox("String is null or empty") Else MsgBox("String is not null or empty") End If End Sub End Class


A string can be null by assigning the value "Nothing" to it, and to check if a string is null or empty, you can use the "IsNullOrEmpty" method.