刚开始学VB 有个地方不懂，过来问下好不？

[quote]Dim toppings As String = ""
If CheckBox1.Checked = True Then
toppings &= "Cheese "
End If
If CheckBox2.Checked = True Then
toppings &= "Peppers "
End If
If CheckBox3.Checked = True Then
toppings &= "Mushrooms"
End If
If toppings <> "" Then
MsgBox("Your pizza has the following toppings: " & toppings)
End If[/quote]
这个是MSDN上关于checkbox的教材里的一个例子，问最后的[quote]If toppings <> "" Then
MsgBox("Your pizza has the following toppings: " & toppings)
End If[/quote]这几行完全看不懂啊！求大哥哥解释！