The FigureSet interface is the interface implemented by any
class that contain references to a set of figures. Some of the
operations are noted as optional -- implementors can throw
an UnsupportedOperation exception if these methods do not make
sense for them.
Test if this set contains the given figure. As a general
rule, the implementation of this method is not required to be
efficient -- O(n) in the length of the list is acceptable.
Clients should note that, in general, a much better way
of making this same test is to check if the parent of the figure
is the same object as this set.
Return an iteration of the figures in this set, in an
undefined order. Generally, an implementor will return figures
from front to back, but if there is a substantially more
efficient way of returning them, then the implementor can
Return an iteration of the figures in this set, from
back to front. This is the order in which
figures should normally be painted.
Return an iteration of the figures in this set, from back to
front. This is the order in which events should normally be