I recently implemented this very pattern in a web application, in which I wanted to represent the current state (in the sense of REST) in such a way that I could say {code} state.getNextPage().getRest() {code} to get the URL which represents "the next page of results". In order to permit construction of arbitrary, unknown future subclasses, I use the factory method. {code} // pseudo-code class StateWithPage implements State { public State getNextPage() { return createState(this.page + 1); } protected State createState(final int page) { return new StateWithPage(page); } } class StateWithPageAndColor extends StateWithPage { protected State createState(final int page) { return new StateWithPageAndColor(page, this.color); } } {code} Jonathan Feinberg Jonathan Feinberg Jonathan Feinberg 2006-02-22 16:10:38.172 2006-02-22 16:10:38.044