How to change the sample in FlatField?

Hi, there,

According to VisAD Java Component Library Developer Guide (http://www.ssec.wisc.edu/~billh/guide.html#3.10), "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?

Suppose we have an isoContour,  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?

thanks,

Kan