public void line(double value,Paint color,float width,boolean stack){
  SourcedPlotElement parent=stack ? findParent() : null;
  plotElements.add(new ConstantLine(value,color,new BasicStroke(width),parent));
}

public void line ( double value , Paint color , float width , boolean stack ) { SourcedPlotElement parent = stack ? findParent ( ) : null ; plotElements . add ( new ConstantLine ( value , color , new BasicStroke ( width ) , parent ) ) ; }
define a line like any other but with constant value , it can be stacked
