Confused about instantiating classes

There is something confusing to me about classes. Suppose I have a form with a textbox and a button on it and I define a class as follows:

Public Class Checktext
Private Shared m_Title As String = "TextBox Error"

Public Shared Property Title() As String
Get
Return m_Title
End Get
Set(ByVal value As String)
m_Title = value
End Set
End Property
Public Shared Function IsValid(ByVal control As Control) As Boolean
If control.GetType.ToString = "System.Windows.Forms.TextBox" Then
Dim textBox As TextBox = CType(control, TextBox)
If textBox.Text = "" Then
MessageBox.Show(textBox.Name.ToString & " cannot be empty.", Title)
textBox.Select()
Return False
Else
MessageBox.Show("That's better", Title)
Return True
End If
Else
MessageBox.Show("This is not a textbox", Title)
Return False
End If
End Function

End Class

The button click method looks like this:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
If Not Checktext.IsValid(TextBox1) Then
TextBox1.Text = "Try again"
End If
End Sub

But I never make an instance of the class. That's the entire project. So why does this code work?

Shared members don't require an instance to use, more over you cannot use Shared members from an instance. e.g. the following code will cause a warning.

Code:

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    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim c As New Checktext
        If Not c.IsValid(TextBox1) Then ' this cause a warning
            TextBox1.Text = "Try again"
        End If
    End Sub

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Ah, OK, then this is like static?

Quote:

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Originally Posted by franceint

Ah, OK, then this is like static?

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It is static.

Quote:

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Originally Posted by franceint

Ah, OK, then this is like static?

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Just note that there is a Static keyword in VB but it means something different. Shared in VB is equivalent to 'static' in C# or other C-based languages and Static in VB is used to make a local variable retain its value between method calls.