Java8

Posted 2020-10-09 咸鱼

 1 import java.util.ArrayList;
 2 import java.util.Arrays;
 3 import java.util.List;
 4 import java.util.function.Predicate;
 5 import java.util.stream.Collectors;
 6 
 7 /**
 8  * java8实战第一章笔记
 9  *
10  * @author shangjinyu
11  * @created 2017/9/29
12  */
13 public class Notes {
14 
15     //构造一个待筛选的list
16     List<Apple> inventory = Arrays.asList(new Apple(80, "green"),
17             new Apple(155, "green"),
18             new Apple(120, "red"));
19 
20     //找出list中的所有的绿色苹果
21     //写法一
22     public List<Apple> filterGreenApples(List<Apple> inventory) {
23         List<Apple> result = new ArrayList<>();
24         for (Apple apple : inventory) {
25             if (apple.getColor().equals("green")) {
26                 result.add(apple);
27             }
28         }
29         return result;
30     }
31 
32     //写法二
33     /*public interface Predicate<T>{
34         boolean test(T t);
35     }
36     一个java8中的函数FunctionInterface接口
37     */
38     public boolean isGreenApple(Apple apple) {
39         return apple.getColor().equals("green");
40     }
41 
42     public List<Apple> filterGreenApples(List<Apple> inventory, Predicate<Apple> p) {
43         List<Apple> result = new ArrayList<>();
44         for (Apple apple : inventory) {
45             if (p.test(apple)) {
46                 result.add(apple);
47             }
48         }
49         return result;
50     }
51 
52     //用法
53     List<Apple> greenApples1 = filterGreenApples(inventory, this::isGreenApple);
54     //lambdasin写法
55     List<Apple> greenApples2 = filterGreenApples(inventory, (Apple apple) -> apple.getColor().equals("green"));
56     List<Apple> greenApples3 = filterGreenApples(inventory, item -> item.getColor().equals("green"));
57     //流
58     //顺序处理
59     List<Apple> greenApples4 = inventory.stream().filter(apple -> apple.getColor().equals("green")).collect(Collectors.toList());
60     //并行处理
61     List<Apple> greenApples5 = inventory.parallelStream().filter(apple -> apple.getColor().equals("green")).collect(Collectors.toList());
62 
63     //一个实体类
64     public class Apple {
65         private int weight = 0;
66         private String color = "";
67 
68         public Apple(int weight, String color) {
69             this.weight = weight;
70             this.color = color;
71         }
72 
73         public Integer getWeight() {
74             return weight;
75         }
76 
77         public void setWeight(Integer weight) {
78             this.weight = weight;
79         }
80 
81         public String getColor() {
82             return color;
83         }
84 
85         public void setColor(String color) {
86             this.color = color;
87         }
88 
89         public String toString() {
90             return "Apple{" +
91                     "color=‘" + color + ‘\‘‘ +
92                     ", weight=" + weight +
93                     ‘}‘;
94         }
95     }
96 }