java8 stream

Posted 2020-11-23 Draymond

java8的stream用户

　　数据准备：

public class Dish {
    public String name;    //菜的名称
    public Boolean vegetaian;  //是否为素
    public Integer calories;   //卡路里
    public Type type;      //类型（肉 鱼 其他）
    public Dish() {
    }
    public Dish(String name, Boolean vegetaian, Integer calories, Type type) {
        this.name = name;
        this.vegetaian = vegetaian;
        this.calories = calories;
        this.type = type;
    }
    public enum Type {MEAT, FISH, OTHER} //肉 鱼 其他
}

 

public class DishList {

    public static List<Dish> getDishList() {
        List<Dish> dishList = 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, 300, Dish.Type.FISH),
                new Dish("salmon", false, 450, Dish.Type.FISH)
        );
        return dishList;
    }
}

　　1：filter

    /**
     * filter 过滤结果为true的
     * 过滤“calories:卡路里”小于500的
     */
    @Test
    public void filter() {
        List<Dish> dishList = DishList.getDishList();
        List<Dish> collect = dishList.stream().filter(dish -> dish.getCalories() < 500).collect(Collectors.toList());
        collect.forEach(System.out::println);
    }

　　2：distinct

    /**
     * 去重:过滤元素相同的
     */
    @Test
    public void distinct() {
        List<Integer> list = Arrays.asList(1, 2, 3, 4, 1, 2);
        list.stream().distinct().forEach(System.out::println);
    }

 

　　3:   skip

  /**
     * skip 跳过前n个
     */
    @Test
    public void skip() {
        List<Dish> dishList = DishList.getDishList();
        dishList.stream().skip(5).forEach(System.out::println);
    }

　　4:    limit

    /**
     * limit 只保留前n个
     */
    @Test
    public void limit() {
        List<Dish> dishList = DishList.getDishList();
        dishList.stream().limit(5).forEach(System.out::println);
    }

　　5:　map

   /**
     * map 映射
     */
    @Test
    public void map() {
        List<Dish> dishList = DishList.getDishList();
        Function<Dish, String> function1 = dish -> dish.getName() + ",";    //转换的结果可以为任意类型与形式
        Function<Dish, String> function2 = Dish::getName;
        List<String> collect = dishList.stream().map(function1).collect(Collectors.toList());
        collect.forEach(System.out::println);
    }

　　6:　flatMap

 

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