如何对 Arraylist 进行排序，使其集合按值列表排序

Question

我有一个 Arraylist，其中包含食谱，每个食谱都包含一个成分列表。食谱显示在 Android 应用的 UI 列表中，用户希望根据他们最喜欢的成分对列表进行排序。

例如这是他们最喜欢的成分列表

1 - Cheese
2 - Potato
3 - Tuna
4 - Chicken

因此，食谱列表应首先显示包含奶酪的所有成分，然后是土豆等。 如何使用 java stream() 存档？

这是我的模型类目前的样子

public class Recipe {

    String[] ingredients;
    private String description;
    private String title;


    public String[] getIngredients() {
        return ingredients;
    }

    public void setIngredients(String[] ingredients) {
        this.ingredients = ingredients;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }
}

.

public class Ingredient {

    String title;

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }
}

Answer 1

您的 Recipe 类没有使用您的 Recipe 类，因此可以修改您的模型以使用成分类。

public class Recipe {
    List<Ingredient> ingredients;
    ...
}

您可以创建自己的比较器来排序食谱是否包含某些成分。

public class ContainsIngredientComparator implements Comparator<Recipe> {

    private Ingredient ingredient;

    public ContainsIngredientComparator(Ingredient ingredient) {
        this.ingredient = ingredient;
    }   

    @Override
    public int compare(Recipe r1, Recipe r2) {
        if (r1.getIngredients().contains(ingredient)) {
            if (r2.getIngredients().contains(ingredient)) {
                return 0;
            } else {
                return -1;
            }
        } else if (r2.getIngredients().contains(ingredient)) {
            return 1;
        } else {
            return 0;
        }
    }
}

现在，您可以为每种成分创建一个比较器并将所有比较器链接起来。您可以使用 Stream API 将收藏夹成分映射到比较器，并使用 thenComparing 链接比较器：

Optional<ContainsIngredientComparator> favoritesComparator = favorites.stream()
        .map(ContainsIngredientComparator::new)
        .reduce((c1, c2) -> (ContainsIngredientComparator) c1.thenComparing(c2));

您可以使用结果比较器对列表进行排序：

List<Recipe> recipeList = // ... get the recipeList
if (favoritesComparator.isPresent()) {
    recipeList.sort(favoritesComparator.get());
}

Answer 2

您可以创建comparatorPotato 和comparatorCheese，然后根据它们进行排序

  static class Recipie {
        List<String> list;

        public Recipie(List<String> list) {
            this.list = list;
        }

        @Override
        public String toString() {
            return list.toString();
        }
    }

    public static void main(String[] args) {
               List<Recipie> recipies = new ArrayList<>();
        recipies.add(new Recipie(Arrays.asList("Cheese", "Potato", "Onions")));
        recipies.add(new Recipie(Arrays.asList("Tuna", "Potato", "Chicken")));
        recipies.add(new Recipie(Arrays.asList("Potato", "Cheese")));
        recipies.add(new Recipie(Arrays.asList("Chicken")));
        recipies.add(new Recipie(Arrays.asList("Chicken", "Potato")));
        recipies.add(new Recipie(Arrays.asList("Cheese", "Tomato")));

        List<Recipie> result = recipies.stream().sorted(Comparator.comparing(r -> !r.list.contains("Potato")))
                .sorted(Comparator.comparing(r -> !r.list.contains("Cheese"))).collect(Collectors.toList());

        System.out.println(result);
    }

，输出

[[Cheese, Potato, Onions], [Potato, Cheese], [Cheese, Tomato], [Tuna, Potato, Chicken], [Chicken, Potato], [Chicken]]