CollectionUtils.java

public class CollectionUtils {
    @Nullable
    public static <C> C highestNumberObject(List<C> list, Class<? extends C> clazz, Function<C, Number> refMethod) {
        C highest = list
                .stream().filter(v -> v.getClass().equals(clazz))
                .max((a,b) -> Integer.max(refMethod.apply((C) a).intValue(), refMethod.apply((C) b).intValue())).orElse(null);

        return highest;
    }

    @Nullable
    public static <N, C> Multiset.Entry<N> mostCommonAttributeEntry(List<C> list, Class<? extends C> clazz, Function<C, N> refMethod) {
        Multiset<N> commons = HashMultiset.create();
        list.stream().filter(action -> action.getClass().equals(clazz)).forEach(action -> commons.add(refMethod.apply((C) action)));

        return commons.entrySet()
                .stream()
                .max(Comparator.comparing(Multiset.Entry::getCount)).orElse(null);
    }

    @Nullable
    public static <C> Number highestNumber(List<C> list, Class<? extends C> clazz, Function<C, Number> refMethod) {
        C highest = highestNumberObject(list, clazz, refMethod);

        if (highest != null)
            return refMethod.apply(highest);

        return null;
    }

    @Nullable
    public static <N, C> N mostCommonAttribute(List<C> list, Class<? extends C> clazz, Function<C, N> refMethod) {
        return Optional.ofNullable(mostCommonAttributeEntry(list, clazz, refMethod)).map(Multiset.Entry::getElement).orElse(null);
    }

    @Nullable
    @SuppressWarnings("unchecked")
    public static <A, B> List<A> allOfType(List<B> list, Class<? extends A> clazz) {
        return (List<A>) list.stream().filter(action -> action.getClass().equals(clazz)).collect(Collectors.toList());
    }
    
    // Stuff from other class I pasted here cus relation
    
    @Nullable
    public <N, C extends Action> N mostCommonAttribute(Class<? extends C> actionClass, Function<C, N> refMethod) {
        Multiset<N> commons = HashMultiset.create();
        this.getPlayerLifetimes().values().stream()
                .flatMap(listContainer -> listContainer.getActions().stream())
                .collect(Collectors.toList())
                .stream().filter(act -> act.getClass().equals(actionClass)).forEach(action -> commons.add(refMethod.apply((C) action)));

        return commons.entrySet()
                .stream()
                .max(Comparator.comparing(Multiset.Entry::getCount)).map(Multiset.Entry::getElement).orElse(null);
    }

    @Nullable
    public <N, C extends Action> N mostCommonAttribute(UUID actor, Class<? extends C> actionClass, Function<C, N> refMethod) {
        Multiset<N> commons = HashMultiset.create();
        this.getPlayerLifetimes().get(actor).stream()
                .flatMap(listContainer -> listContainer.getActions().stream())
                .collect(Collectors.toList())
                .stream().filter(act -> act.getClass().equals(actionClass)).forEach(action -> commons.add(refMethod.apply((C) action)));

        return commons.entrySet()
                .stream()
                .max(Comparator.comparing(Multiset.Entry::getCount)).map(Multiset.Entry::getElement).orElse(null);
    }
}