Gets the top index.
<p>
The top index is the index of the fully visible line that is currently
at the top of the widget or the topmost partially visible line if no line is fully visible.
The top index changes when the widget is scrolled. Indexing is zero based.
</p>
@return the index of the top line
@exception SWTException <ul>
<li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
<li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
</ul>
Gets the top index. <p> The top index is the index of the fully visible line that is currently at the top of the widget or the topmost partially visible line if no line is fully visible. The top index changes when the widget is scrolled. Indexing is zero based. </p>
@return the index of the top line @exception SWTException <ul> <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li> <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li> </ul>