mira use lo que dices y me salio el siguiente error 
Cita: Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.
Source Error:
Line 108: e.Item.ItemType = ListItemType.Item Then
Line 109: Dim hyper As HyperLink = CType(e.Item.FindControl("hyperLink1"), HyperLink)
Line 110: hyper.Attributes.Add("onclick", txtFecha.Text = "holass")
Line 111: End If
Line 112:
espero que me puedas o puedan ayudar
Nota : si alguien logro poder invocar una funcion java mediante el Hyperlink Colum seria fantastico 