get information of which line is hidden/collapse in editor

hi
  how to get information of which line is hidden/collapse in editor? I use the following code to get character colour, but no information of which line is hidden

HighlightsContainer hc = HighlightingManager.getInstance(jtc).getBottomHighlights();
HighlightsSequence hq = hc.getHighlights(0, document.getLength());
while (hq.moveNext()) {
	AttributeSet as = hq.getAttributes();
	Color color=as.getAttribute(StyleConstants.Foreground);
}	

thanks
from Peter