Filtering immutable/unmodifiable collections

Question

Hi,
I need a general purpose collection filter:
Given a collection, return another collection that excludes certain members of the first collection. Additionally I'd prefer that the new collection retains other attributes of the original (e.g. Comparator if SortedSet etc).
I considered cloning the given collection and then removing undesired elements. Is there a clean way to do this?
In jakarta commons I notice something that comes close (http://cvs.apache.org/viewcvs.cgi/*checkout*/jakarta-commons/collections/src/java/org/apache/commons/collections/CollectionUtils.java), however it modifies the original collection.
     * Filter the collection by applying a Predicate to each element. If the
     * predicate returns false, remove the element.
     * <p>
     * If the input collection or predicate is null, there is no change made.
     * @param collection  the collection to get the input from, may be null
     * @param predicate  the predicate to use as a filter, may be null
    public static void filter(Collection collection, Predicate predicate) {
        if (collection != null && predicate != null) {
            for (Iterator it = collection.iterator(); it.hasNext();) {
                if (predicate.evaluate(it.next()) == false) {
                    it.remove();

Answer 1

copy constructors. I can't remember the last time I
made a class I wrote cloneable.Me neither :) However, I frequently use existing clone() methods in the collections framework (e.g. Vector.clone() etc.)
Is there a reason you need a completely generic
method
to do this? (other than the appeal of writing
beautiful code).I'm writing a utility. I don't want to build in restrictions if I can help it.
Do you actually have an application that requires
this
functionality where you actually use every collection
type?Not sure I get your drift ... The client application currently uses Vector(legacy), ArrayList, HashSet, TreeSet and LinkedHashSet (no LinkedList yet). So there aren't too many implmentations at all. However, I'd like the filter method to be general (see above).
And .clone() won't work for some reason?Can I clone/copy without code like:
if(collection instanceof <particular-collection-implementation>) {
}which I'm trying to avoid (for reasons above) ?