+1 for the static factory method approach like the Collections static methods. These methods could go nicely in the existing CollecitonUtils class.
We already have a ProxyMap which is useful for this kind of thing; maybe we could add ProxyList and ProxySet and use those in the implementations of the factory methods? James ----- Original Message ----- From: "Jack, Paul" <[EMAIL PROTECTED]> To: "'Jakarta Commons Developers List'" <[EMAIL PROTECTED]> Sent: Thursday, April 25, 2002 5:44 PM Subject: RE: [Collections][SUBMIT] TypedList > > I agree. I think one of the benefits of the Proxy pattern is that one > > proxy can be wrapped inside another. So PredicatedList and > > TransformingList would be separate classes, since they represent two > > different responsibilities. If you want to do both, put one inside the > > other. > > I agree here too. Having them in separate classes would also allow me > to control what order things happen in: > > new PredicateList(new TransformList(transform, list), predicate) > new TransformList(new PredicateList(predicate, list), transform) > > The above could do different things. If I predicate first, I can strip > out illegal values to my transform; or, I might be using a transform > that can produce null values that I don't want stored in my list, so > I'd predicate afterwards; or both; I think this is a much more flexible > pattern. > > Having said all that, I think we should keep in mind that if we want to > be complete, we're talking about adding fourteen new classes: > > PredicateBag > PredicateCollection > PredicateList > PredicateMap > PredicateSet > PredicateSortedMap > PredicateSortedSet > TransformBag > TransformCollection > TransformList > TransformMap > TransformSet > TransformSortedMap > TransformSortedSet > > Seems like a lot to include in the public API. Instead I'd advocate doing > what java.util.Collections does; have one class (maybe WrapperUtils? Or > maybe > within CollectionUtils?) that provides static methods for returning wrapped > collections: > > public static List predicateList(List list, Predicate predicate); > // other fourteen similar methods... > > We could then hide the fourteen implementation classes either by making them > inner classes of WrapperUtils or by giving them package scope. > > Having the classes themselves exposed in the public API seems wasteful, as > they're difficult to subclass (unless we also expose the sublist, submap, > collection view and iterator classes -- dozens more) and are meant for > composition. > > -Paul > > > > -- > To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]> > For additional commands, e-mail: <mailto:[EMAIL PROTECTED]> _________________________________________________________ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com -- To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]> For additional commands, e-mail: <mailto:[EMAIL PROTECTED]>
