[rules-users] property change listener for collections

hello, when I have a bean and I want to use a property change listener for collection members, how can I tell the listener the old state of the collection? This is the code for simple fields from the docs: public void setState(final String newState) { String oldState = this.state; this.state = newState; this.changes.firePropertyChange( "state", oldState, newState ); } and now I want to hook in the firePropertyChange for the following method which adds some elements to a set: protected Set<Var> knownVariables = new HashSet<Var>(); public void addKnownVariable(String var) { this.knownVariables.add(var); changes.firePropertyChange("knownVariables", OLDSTATE??!, knownVariables); } Will I have to copy the whole collection, switch the complete field collection object that I can supply the "old state"? thanks, Andy