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Java8：使用Lambda表达式增强版Comparator排序

news 来源：原创 2024/4/19 23:58:01

学习路上的自我记录-------路好长，就问你慌不慌，大声港，不慌。----jstarseven。

实体类：

 1 package com.server.model;
 2 
 3 /**
 4  * Created by jstarseven on 2016/3/21.
 5  */
 6 public class Human {
 7 
 8     private String name;
 9     private int age;
10 
11     @Override
12     public String toString() {
13         return "Human{" +
14                 "name='" + name + '\'' +
15                 ", age=" + age +
16                 '}';
17     }
18 
19     public Human() {
20         super();
21     }
22 
23     public Human(final String name, final int age) {
24         super();
25         this.name = name;
26         this.age = age;
27     }
28 
29     public String getName() {
30         return name;
31     }
32 
33     public void setName(String name) {
34         this.name = name;
35     }
36 
37     public int getAge() {
38         return age;
39     }
40 
41     public void setAge(int age) {
42         this.age = age;
43     }
44 
45     public static int compareByNameThenAge(Human lhs, Human rhs) {
46         if (lhs.getName().equals(rhs.getName())) {
47             return lhs.getAge() - rhs.getAge();
48         } else {
49             return lhs.getName().compareTo(rhs.getName());
50         }
51     }
52 
53 
54 }

View Code

测试类：

  1 package com.server.lambda;
  2 
  3 import com.server.model.Human;
  4 import org.junit.Test;
  5 
  6 import java.util.ArrayList;
  7 import java.util.Collections;
  8 import java.util.Comparator;
  9 import java.util.List;
 10 
 11 /**
 12  * Created by jstarseven on 2016/3/21.
 13  */
 14 public class TestLambda {
 15 
 16     //    不使用Lambda表达式的基本排序
 17     @Test
 18     public void givenPreLambda_whenSortingEntitiesByName_thenCorrectlySorted() {
 19 
 20         List<Human> humans = new ArrayList();
 21         humans.add(new Human("A", 10));
 22         humans.add(new Human("C", 14));
 23         humans.add(new Human("C", 12));
 24         humans.add(new Human("B", 12));
 25         Collections.sort(humans, new Comparator<Human>() {
 26             public int compare(Human o1, Human o2) {
 27                 return o1.getName().compareTo(o2.getName());
 28             }
 29         });
 30         for (Human bean : humans) {
 31             System.out.println(bean.toString());
 32         }
 33     }
 34 
 35 
 36     //    使用Lambda表达式的基本排序
 37     @Test
 38     public void whenSortingEntitiesByName_thenCorrectlySorted() {
 39         List<Human> humans = new ArrayList();
 40         humans.add(new Human("A", 10));
 41         humans.add(new Human("C", 14));
 42         humans.add(new Human("C", 12));
 43         humans.add(new Human("B", 12));
 44         humans.sort((Human h1, Human h2) -> h1.getName().compareTo(h2.getName()));
 45         for (Human bean : humans) {
 46             System.out.println(bean.toString());
 47         }
 48     }
 49 
 50 
 51     //    没有类型定义（ Type Definitions）的基本排序
 52     @Test
 53     public void givenLambdaShortForm_whenSortingEntitiesByName_thenCorrectlySorted() {
 54         List<Human> humans = new ArrayList();
 55         humans.add(new Human("A", 10));
 56         humans.add(new Human("C", 14));
 57         humans.add(new Human("C", 12));
 58         humans.add(new Human("B", 12));
 59         humans.sort((h1, h2) -> h1.getName().compareTo(h2.getName()));
 60         for (Human bean : humans) {
 61             System.out.println(bean.toString());
 62         }
 63     }
 64 
 65     //    使用静态方法的引用来排序
 66     @Test
 67     public void givenMethodDefinition_whenSortingEntitiesByNameThenAge_thenCorrectlySorted() {
 68         List<Human> humans = new ArrayList();
 69         humans.add(new Human("A", 10));
 70         humans.add(new Human("C", 14));
 71         humans.add(new Human("C", 12));
 72         humans.add(new Human("B", 12));
 73         humans.sort(Human::compareByNameThenAge);
 74         for (Human bean : humans) {
 75             System.out.println(bean.toString());
 76         }
 77     }
 78 
 79     //    提取Comparator进行排序
 80     @Test
 81     public void givenInstanceMethod_whenSortingEntitiesByNameThenAge_thenCorrectlySorted() {
 82         List<Human> humans = new ArrayList();
 83         humans.add(new Human("A", 10));
 84         humans.add(new Human("C", 14));
 85         humans.add(new Human("C", 12));
 86         humans.add(new Human("B", 12));
 87         Collections.sort(humans, Comparator.comparing(Human::getName));
 88         for (Human bean : humans) {
 89             System.out.println(bean.toString());
 90         }
 91     }
 92 
 93     //    反转排序
 94     @Test
 95     public void whenSortingEntitiesByNameReversed_thenCorrectlySorted() {
 96         List<Human> humans = new ArrayList();
 97         humans.add(new Human("A", 10));
 98         humans.add(new Human("C", 14));
 99         humans.add(new Human("C", 12));
100         humans.add(new Human("B", 12));
101         Comparator<Human> comparator = (h1, h2) -> h1.getName().compareTo(h2.getName());
102 
103         humans.sort(comparator.reversed());
104         for (Human bean : humans) {
105             System.out.println(bean.toString());
106         }
107     }
108 
109     //    多条件排序
110     @Test
111     public void whenSortingEntitiesByNameThenAge_thenCorrectlySorted() {
112         List<Human> humans = new ArrayList();
113         humans.add(new Human("A", 10));
114         humans.add(new Human("C", 14));
115         humans.add(new Human("C", 12));
116         humans.add(new Human("B", 12));
117         humans.sort((lhs, rhs) -> {
118             if (lhs.getName().equals(rhs.getName())) {
119                 return lhs.getAge() - rhs.getAge();
120             } else {
121                 return lhs.getName().compareTo(rhs.getName());
122             }
123         });
124         for (Human bean : humans) {
125             System.out.println(bean.toString());
126         }
127     }
128 
129     //    多条件组合排序
130     @Test
131     public void givenComposition_whenSortingEntitiesByNameThenAge_thenCorrectlySorted() {
132         List<Human> humans = new ArrayList();
133         humans.add(new Human("A", 10));
134         humans.add(new Human("C", 14));
135         humans.add(new Human("C", 12));
136         humans.add(new Human("B", 12));
137         humans.sort(Comparator.comparing(Human::getName).thenComparing(Human::getAge));
138         for (Human bean : humans) {
139             System.out.println(bean.toString());
140         }
141     }
142 }