关于Java8:StreamAPI的一点记录

关于 Stream ,Functional Interface 的一点记录

 

stream对于集合操作的便捷度提升:

 

 1 import java.util.ArrayList;
 2 import java.util.List;
 3 import java.util.Map;
 4 import java.util.stream.Collectors;
 5 
 6 public class ActiveMac {
 7     
 8     public static void main(String[] args) {
 9         List<Human> humans = new ArrayList<>();
10         humans.add(new Human("Daniel", 23, "Google"));
11         humans.add(new Human("Max", 33, "Microsoft"));
12         humans.add(new Human("Jenny", 18, "Google"));
13         humans.add(new Human("Alex", 28, "Facebook"));
14         humans.add(new Human("Charles", 34, "Twitter"));
15         humans.add(new Human("Roy", 31, "Microsoft"));
16         
17         // 对集合内符合条件的计数
18         long nums = humans.stream().filter(human -> (human.getAge() > 20)).count();
19         System.out.println("nums:" + nums);
20         
21         // 对集合内符合条件的筛选输出
22         List<Human> nameContE = humans.stream().filter(human -> human.getName().contains("e")).collect(Collectors.toList());
23         System.out.println("nameContainsE:" + nameContE.toString());
24         
25         // 对集合内元素中元素进行操作
26         List<Integer> doubleAge = humans.stream().map(human -> human.getAge() * 2).collect(Collectors.toList());
27         System.out.println("doubleAge:" + doubleAge.toString());
28         
29         // 对集合内元素分组
30         Map<String, List<Human>> group = humans.stream().collect(Collectors.groupingBy(Human::getCompany));
31         System.out.println(group.toString());
32     }
33 }
34 
35 class Human {
36     private String name;
37     private Integer age;
38     private String company;
39     
40     public Human(String name, Integer age, String company) {
41         super();
42         this.name = name;
43         this.age = age;
44         this.company = company;
45     }
46     
47     public String getName() {
48         return name;
49     }
50     
51     public void setName(String name) {
52         this.name = name;
53     }
54     
55     public Integer getAge() {
56         return age;
57     }
58     
59     public void setAge(Integer age) {
60         this.age = age;
61     }
62     
63     public String getCompany() {
64         return company;
65     }
66     
67     public void setCompany(String company) {
68         this.company = company;
69     }
70     
71     @Override
72     public String toString() {
73         return name + "-" + age + "-" + company;
74     }
75 }

 

新旧方法的对比:

        // 1.对集合内符合条件的计数
        long nums = humans.stream().filter(human -> (human.getAge() > 20)).count();
        System.out.println(nums);
        
        // 2.对集合内符合条件的筛选输出
        List<Human> nameContE = humans.stream().filter(human -> human.getName().contains("e")).collect(Collectors.toList());
        System.out.println(nameContE.toString());
        
        // 3.对集合内元素中元素进行操作
        List<Integer> doubleAge = humans.stream().map(human -> human.getAge() * 2).collect(Collectors.toList());
        System.out.println(doubleAge.toString());
        
        // 4.对集合内元素分组
        Map<String, List<Human>> group = humans.stream().collect(Collectors.groupingBy(Human::getCompany));
        System.out.println(group.toString());
        
        // 1
        int num = 0;
        for (Human h : humans) {
            if (h.getAge() > 20) {
                num++;
            }
        }
        System.out.println(num);
        
        
        
        
        
        //旧方法-循环
        // 2
        List<Human> eResult = new ArrayList<>();
        for (Human h : humans) {
            if (h.getName().contains("e")) {
                eResult.add(h);
            }
        }
        System.out.println(eResult.toString());
        
        // 3
        List<Integer> dounleA = new ArrayList<>();
        for (Human h : humans) {
            Integer newAge = h.getAge() * 2;
            dounleA.add(newAge);
        }
        System.out.println(dounleA.toString());
        
        // 4
        Map<String, List<Human>> maps = new HashMap<>();
        for (Human h : humans) {
            List<Human> hs = new ArrayList<>();
            String key = h.getCompany();
            if (maps.containsKey(key)) {
                hs = maps.get(key);
            }
            hs.add(h);
            maps.put(key, hs);
        }
        System.out.println(maps.toString());
        
    }

 

输出结果方面并不存在差异

 

新方法-stream
5 [Daniel-23-Google, Jenny-18-Google, Alex-28-Facebook, Charles-34-Twitter] [46, 66, 36, 56, 68, 62] {Google=[Daniel-23-Google, Jenny-18-Google], Twitter=[Charles-34-Twitter], Microsoft=[Max-33-Microsoft, Roy-31-Microsoft], Facebook=[Alex-28-Facebook]}

旧方法-循环
5 [Daniel-23-Google, Jenny-18-Google, Alex-28-Facebook, Charles-34-Twitter] [46, 66, 36, 56, 68, 62] {Google=[Daniel-23-Google, Jenny-18-Google], Twitter=[Charles-34-Twitter], Microsoft=[Max-33-Microsoft, Roy-31-Microsoft], Facebook=[Alex-28-Facebook]}

 

其他的下次记录

posted @ 2018-01-15 10:15  世间草木  阅读(240)  评论(0编辑  收藏  举报