Returns the y-coordinate (in Java2D space) of the center of the pie
chart. For the
PiePlot3D class, we derive this from the top of
the pie.
The y-coordinate (in Java2D space).
Sets the y-coordinate of the center of the pie chart. This method is
used by the plot and typically is not called directly by applications.
Parameters: y - the y-coordinate (in Java2D space).