How can I change policy permissions at RUNTIME?

How can I change policy permissions at runtime?For example giving write permission for a file to a subject and some time latter removing this permission, all at the same runtime?
[206 byte] By [Alisa] at [2007-11-27 3:07:39]
# 1
I think you'll have to implement your own Policy class, or find one somewhere that supports dynamic permission collections.
ejpa at 2007-7-12 3:54:59 > top of Java-index,Security,Other Security APIs, Tools, and Issues...