filter and sort list using google collections

Question

Suppose I have a list (or Set):

List testList = Lists.newArrayList(\"assocX\",\"srcT\",\"destA\",\"srcX\", \"don\'t care Y\", \"garbage\", \"sr         


        

Answer 1

As long as those three prefixes are the only things you care about, I'd suggest something like this:

    Predicate filter = new Predicate() {
        @Override
        public boolean apply(String input) {
            return input.startsWith("src") || input.startsWith("assoc") || input.startsWith("dest");
        }
    };

    Function assignWeights = new Function() {
        @Override
        public Integer apply(String from) {
            if (from.startsWith("src")) {
                return 0;
            } else if (from.startsWith("assoc")) {
                return 1;
            } else if (from.startsWith("dest")) {
                return 2;
            } else {
                /* Shouldn't be possible but have to do something */
                throw new IllegalArgrumentException(from + " is not a valid argument");
            }
        }
    };

    ImmutableList sortedFiltered = ImmutableList.copyOf(
            Ordering.natural().onResultOf(assignWeights).sortedCopy(
                    Iterables.filter(testList, filter)
            )
    );

This solution definitely wouldn't scale out incredibly well if you start adding more prefixes to filter out or sort by, since you'd have to continually update both the filter and the weight of each prefix.