Java8基础知识整理----stream_01

忘是亡心i 2023-06-04 06:55 118阅读 0赞

**需求：返回低热量的菜肴  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3NjA2OTAx_size_16_color_FFFFFF_t_70]![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3NjA2OTAx_size_16_color_FFFFFF_t_70 1]对了先补上菜肴实体类Dish**

package lambdasinaction.chap4;
    import java.util.*;
    
    public class Dish { 
    
        private final String name;
        private final boolean vegetarian;
        private final int calories;
        private final Type type;
    
        public Dish(String name, boolean vegetarian, int calories, Type type) { 
            this.name = name;
            this.vegetarian = vegetarian;
            this.calories = calories;
            this.type = type;
        }
    
        public String getName() { 
            return name;
        }
    
        public boolean isVegetarian() { 
            return vegetarian;
        }
    
        public int getCalories() { 
            return calories;
        }
    
        public Type getType() { 
            return type;
        }
    
        public enum Type {  MEAT, FISH, OTHER }
    
        @Override
        public String toString() { 
            return name;
        }
    
        public static final 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));
    }

Stream的基本操作：

package lambdasinaction.chap4;
    
    import java.util.*;
    import java.util.stream.*;
    
    import static java.util.Comparator.comparing;
    import static java.util.stream.Collectors.toList;
    
    import static lambdasinaction.chap4.Dish.menu;
    
    public class StreamBasic { 
    
        public static void main(String...args){ 
            // Java 7
            getLowCaloricDishesNamesInJava7(Dish.menu).forEach(System.out::println);
    
            System.out.println("---------------------------------------------------");
    
            // Java 8
            getLowCaloricDishesNamesInJava8(Dish.menu).forEach(System.out::println);
    
        }
    
        public static List<String> getLowCaloricDishesNamesInJava7(List<Dish> dishes){ 
            List<Dish> lowCaloricDishes = new ArrayList<>();
            for(Dish d: dishes){ 
                if(d.getCalories() > 400){ 
                    lowCaloricDishes.add(d);
                }
            }
            List<String> lowCaloricDishesName = new ArrayList<>();
            Collections.sort(lowCaloricDishes, new Comparator<Dish>() { 
                public int compare(Dish d1, Dish d2){ 
                    return Integer.compare(d1.getCalories(), d2.getCalories());
                }
            });
            for(Dish d: lowCaloricDishes){ 
                lowCaloricDishesName.add(d.getName());
            }
            return lowCaloricDishesName;
        }
    
        public static List<String> getLowCaloricDishesNamesInJava8(List<Dish> dishes){ 
            return dishes.stream()
                    .filter(d -> d.getCalories() > 400)
                    .sorted(comparing(Dish::getCalories))
                    .map(Dish::getName)
                    .collect(toList());
        }
    }

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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM3NjA2OTAx_size_16_color_FFFFFF_t_70 1]: /images/20230601/e3d842dc4fe94ebd9f7a15380e571cf4.png