Java8_Chapter04

 1 import static java.util.Comparator.comparing;
 2 import static java.util.stream.Collectors.toList;
 3 
 4 import java.util.ArrayList;
 5 import java.util.Collections;
 6 import java.util.Comparator;
 7 import java.util.List;
 8 
 9 /**
10  * 在这里编写类的功能描述
11  *
12  * @author shangjinyu
13  * @created 2017/10/4
14  */
15 public class Notes {
16     //和迭代器类似,流只能遍历一次
17 
18     public static List<String> getLowCaloricDishesNamesInJava7(List<Dish> dishes){
19         List<Dish> lowCaloricDishes = new ArrayList<>();
20         for(Dish d: dishes){
21             if(d.getCalories() > 400){
22                 lowCaloricDishes.add(d);
23             }
24         }
25         List<String> lowCaloricDishesName = new ArrayList<>();
26         Collections.sort(lowCaloricDishes, new Comparator<Dish>() {
27             public int compare(Dish d1, Dish d2){
28                 return Integer.compare(d1.getCalories(), d2.getCalories());
29             }
30         });
31         for(Dish d: lowCaloricDishes){
32             lowCaloricDishesName.add(d.getName());
33         }
34         return lowCaloricDishesName;
35     }
36 
37     public static List<String> getLowCaloricDishesNamesInJava8(List<Dish> dishes){
38         return dishes.stream()
39                 .filter(d -> d.getCalories() > 400)
40                 .sorted(comparing(Dish::getCalories))
41                 .map(Dish::getName)
42                 .collect(toList());
43     }
44     public static List<String> getLowCaloricDishesNamesInJava8withLambda1(List<Dish> dishes){
45         return dishes.stream()
46                 .filter(d -> d.getCalories() > 400)
47                 .sorted(Comparator.comparing(Dish::getCalories))
48                 .map(a -> a.getName())
49                 .collect(toList());
50     }
51     public static List<String> getLowCaloricDishesNamesInJava8withLambda2(List<Dish> dishes){
52         return dishes.stream()
53                 .filter(d -> d.getCalories() > 400)
54                 .sorted((a,b) -> Integer.compare(a.getCalories(), b.getCalories()))
55                 .map(a -> a.getName())
56                 .collect(toList());
57     }
58     public static List<String> names = Dish.menu.stream()
59             .filter(d -> {
60                 System.out.println("filtering " + d.getName());
61                 return d.getCalories() > 300;
62             }).map(d -> {
63                 System.out.println("mapping " + d.getName());
64                 return d.getName();
65             }).limit(3)
66             .collect(toList());
67     /**
68      * System.out.println(names);
69      * filtering pork
70      * mapping pork
71      * filtering beef
72      * mapping beef
73      * filtering chicken
74      * mapping chicken
75      * [pork, beef, chicken]
76      */
77     public static void main(String...args){
78         System.out.println("---");
79         // Java 7
80         getLowCaloricDishesNamesInJava7(Dish.menu).forEach(System.out::println);
81         System.out.println("---");
82         // Java 8
83         getLowCaloricDishesNamesInJava8(Dish.menu).forEach(System.out::println);
84         System.out.println(names);
85     }
86 }