Java Streams在reduce之后对值进行排序

Question

我只是试着理解Java中的流,并且我坚持排序阶段.我的目的是用一条流来获得最昂贵的蔬菜披萨.在这一点上,我得到披萨价格,但我无法对它进行排序.谁能告诉我应该怎么做呢？

我尝试这个:

pizzas.stream()
    .flatMap(pizza -> Stream.of(pizza.getIngredients())
        .filter(list -> list.stream().noneMatch(Ingredient::isMeat))
            .map(list -> list.stream().map(Ingredient::getPrice).reduce(0,(a, b) -> a + b))
            .sorted((o1, o2) -> o1.intValue() - o2.intValue())
            )
    .forEach(System.out::println);

此代码返回未分类的比萨饼值.

Answer 1

import java.util.Collection;
import java.util.Comparator;

interface Pizza {
    interface Ingredient {
        boolean isMeat();

        int getPrice();
    }

    Collection<Ingredient> getIngredients();

    static boolean isVegetarian(Pizza pizza) {
        return pizza.getIngredients().stream().noneMatch(Ingredient::isMeat);
    }

    static int price(Pizza pizza) {
        return pizza.getIngredients().stream().mapToInt(Ingredient::getPrice).sum();
    }

    static Pizza mostExpensiveVegetarianPizza(Collection<Pizza> pizzas) {
        return pizzas.stream()
                     .filter(Pizza::isVegetarian)
                     .max(Comparator.comparingInt(Pizza::price))
                     .orElseThrow(() -> new IllegalArgumentException("no veggie pizzas"));
    }
}

如果你想Ingredient.getPrice()返回a double,你会使用Stream.mapToDouble()in Pizza.price()和Comparator.comparingDouble()in Pizza.mostExpensiveVegetarianPizza().