question: public void drawDomainMarker ( Graphics2D g2 , ContourPlot plot , ValueAxis domainAxis , Marker marker , Rectangle2D dataArea ) { if ( marker instanceof ValueMarker ) { ValueMarker vm = ( ValueMarker ) marker ; double value = vm . getValue ( ) ; Range range = domainAxis . getRange ( ) ; if ( ! range . contains ( value ) ) { return ; } double x = domainAxis . valueToJava2D ( value , dataArea , RectangleEdge . BOTTOM ) ; Line2D line = new Line2D . Double ( x , dataArea . getMinY ( ) , x , dataArea . getMaxY ( ) ) ; Paint paint = marker . getOutlinePaint ( ) ; Stroke stroke = marker . getOutlineStroke ( ) ; g2 . setPaint ( paint != null ? paint : Plot . DEFAULT_OUTLINE_PAINT ) ; g2 . setStroke ( stroke != null ? stroke : Plot . DEFAULT_OUTLINE_STROKE ) ; g2 . draw ( line ) ; } }
target:  Draws a vertical line on the chart to represent a 'range marker'.