What is the difference between vbNullString, String.Empty and ""?

Question

All of these

• txtUsername.Text <> vbNullString
• txtUsername.Text <> String.Empty
• txtUsername.Text <> ""

seem to return the same result. So, what's the difference between vbNullString, String.Empty and ""?

Answer 1

vbNullString is a constant, more likely out of VB6, String.Empty and "" are the same, some say that there is a performance difference, but that is not true, it is your choice what you use.

To check whether a string is empty you can use If String.IsNullOrEmpty(String). The advantage is that it will also check for null, because string is a class and because of this a reference type.