void (String[] args) { List<Dish> menu = Arrays.asList( new Dish("pork", false, 800, Dish.Type.MEAT), new Dish("beef", false, 700, Dish.Type.MEAT), new Dish("chicken", false, 400, Dish.Type.MEAT), new Dish("french fries", true, 530, Dish.Type.OTHER), new Dish("rice", true, 350, Dish.Type.OTHER), new Dish("season fruit", true, 120, Dish.Type.OTHER), new Dish("pizza", true, 550, Dish.Type.OTHER), new Dish("prawns", false, 400, Dish.Type.FISH), new Dish("salmon", false, 450, Dish.Type.FISH) ); System.out.println( menu.stream().collect(reducing(0, Dish::getCalories, (Integer i, Integer j) -> i + j)) ); System.out.println( menu.stream().collect( groupingBy(Dish::getType, mapping( dish -> { if (dish.getCalories() <= 400) return CaloricLevel.DIET; else if (dish.getCalories() <= 700) return CaloricLevel.NORMAL; else return CaloricLevel.FAT; }, toSet()))) ); System.out.println( menu.stream().collect( groupingBy(Dish::getType, collectingAndThen( reducing((d1, d2) -> d1.getCalories() > d2.getCalories() ? d1 : d2), Optional::get))) ); }