How to change the sample in FlatField?

<HTML><P>Hi, there, </P>
<P>According to VisAD Java Component Library Developer Guide (<A 
href="http://www.ssec.wisc.edu/~billh/guide.html#3.10";>http://www.ssec.wisc.edu/~billh/guide.html#3.10</A>),
 "Most Data classes and metadata classes (of FlatField) are immutable", does it 
mean that users cannot interactively change the sample of a FlatField? In other 
words, is the following job possible?</P>
<P>Suppose we have an isoContour,&nbsp;&nbsp;is it possible to allow the user 
to change the isoline by clicking mouse button? Since the isoContour is related 
to the sample of the FlatField, the above question is equivalent to change the 
sample of the field. Is that possible? If so, can anyone give me an instruction 
how to do it?</P>
<P>thanks,</P>
<P>Kan</P>
<P>&nbsp;</P></HTML>