Strain.java

import java.util.ArrayList;
import java.util.List;
import java.util.function.Predicate;

public class Strain {

	public static <T> List<T> keep(List<T> collection, Predicate<T> predicate) {
		return filter(collection, predicate);
	}

	public static <T> List<T> discard(List<T> collection, Predicate<T> predicate) {
		return filter(collection, predicate.negate());
	}

	public static <T> List<T> filter(List<T> collection, Predicate<T> predicate) {
		List<T> filteredCollection = new ArrayList<>();

		for (T item : collection) {
			if (predicate.test(item)) {
				filteredCollection.add(item);
			}
		}

		return filteredCollection;
	}
}