What is the best way to filter a Java Collection?

Question

I want to filter a java.util.Collection based on a predicate.

Answer 1

I needed to filter a list depending on the values already present in the list. For example, remove all values following that is less than the current value. {2 5 3 4 7 5} -> {2 5 7}. Or for example to remove all duplicates {3 5 4 2 3 5 6} -> {3 5 4 2 6}.

public class Filter {
    public static  void List(List list, Chooser chooser) {
        List toBeRemoved = new ArrayList<>();
        leftloop:
        for (int right = 1; right < list.size(); ++right) {
            for (int left = 0; left < right; ++left) {
                if (toBeRemoved.contains(left)) {
                    continue;
                }
                Keep keep = chooser.choose(list.get(left), list.get(right));
                switch (keep) {
                    case LEFT:
                        toBeRemoved.add(right);
                        continue leftloop;
                    case RIGHT:
                        toBeRemoved.add(left);
                        break;
                    case NONE:
                        toBeRemoved.add(left);
                        toBeRemoved.add(right);
                        continue leftloop;
                }
            }
        }

        Collections.sort(toBeRemoved, new Comparator() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return o2 - o1;
            }
        });

        for (int i : toBeRemoved) {
            if (i >= 0 && i < list.size()) {
                list.remove(i);
            }
        }
    }

    public static  void List(List list, Keeper keeper) {
        Iterator iterator = list.iterator();
        while (iterator.hasNext()) {
            if (!keeper.keep(iterator.next())) {
                iterator.remove();
            }
        }
    }

    public interface Keeper {
        boolean keep(E obj);
    }

    public interface Chooser {
        Keep choose(E left, E right);
    }

    public enum Keep {
        LEFT, RIGHT, BOTH, NONE;
    }
}

This will bee used like this.

List names = new ArrayList<>();
names.add("Anders");
names.add("Stefan");
names.add("Anders");
Filter.List(names, new Filter.Chooser() {
    @Override
    public Filter.Keep choose(String left, String right) {
        return left.equals(right) ? Filter.Keep.LEFT : Filter.Keep.BOTH;
    }
});