Java中的sort

Posted 2020-11-30 何去何从gw

Java中对集合排序有两种方式

Comparable和Comparator

public static <T> void sort(List<T> list); 将集合中的数据按照默认规则进行排序 (我们在自己的类里面实现Comparabl接口方法compareTo)
public static <T> void sort(List<T> list, Comparator<? super T>); 将集合中的数据按照指定规则进行排序

 

 1 /**
 2  * @author gw
 3  * @date 2019/11/5 0005 下午 22:15
 4  */
 5 
 6 /*
 7  * public static<T> void sort(List<T> list); 将集合中的数据按照默认规则进行排序
 8  *
 9  * 注意:
10  *      sort使用前提:被排序的集合里面存储的元素,必须实现Comparable(接口),重写接口中的方法compareTo,定义排序规则
11  *
12  *      升序: this - 参数
13  *            return 0;就是按照原来顺序输出
14  *
15  *
16  * */
17 public class Demo02Sort {
18     public static void main(String[] args) {
19         ArrayList<Person> objects = new ArrayList<>();
20         objects.add(new Person("小明", 23));
21         objects.add(new Person("小红", 24));
22         objects.add(new Person("小绿", 22));
23 
24         System.out.println("objects = " + objects);
25         Collections.sort(objects);
26         System.out.println("objects = " + objects);
27     }
28 }
29 
30 
31 class Person implements Comparable<Person> {
32     private String name;
33     private int age;
34 
35     @Override
36     public int compareTo(Person person) {
37 //        return 0;
38         return this.getAge() - person.getAge();
39 
40     }
41 
42     @Override
43     public String toString() {
44         return "Person{" +
45                 "name=‘" + name + ‘‘‘ +
46                 ", age=" + age +
47                 ‘}‘;
48     }
49 
50     public Person() {
51     }
52 
53     public Person(String name, int age) {
54         this.name = name;
55         this.age = age;
56     }
57 
58     public String getName() {
59         return name;
60     }
61 
62     public void setName(String name) {
63         this.name = name;
64     }
65 
66     public int getAge() {
67         return age;
68     }
69 
70     public void setAge(int age) {
71         this.age = age;
72     }
73 }

Comparable

 

 1 /**
 2  * @author gw
 3  * @date 2019/11/5 0005 下午 22:40
 4  */
 5 
 6 
 7 /*
 8  * Comparator
 9  * Comparable都是接口
10  *
11  * public static <T> void sort(List<T> list, Comparator<? super T> c)
12  *
13  * Comparable: 我们的类继承Comparable接口,然后实现里面的CompareTo方法,
14  *             如何调用:Collections.sort(arrayList)
15  *
16  * Comparator: 我们的类不用继承Comparable接口,也不用继承Comparator接口
17  *             如何调用:Collections.sort(objects, new Comparator<Person1>() {  // 匿名类
18                         @Override
19                         public int compare(Person1 person1, Person1 t1) {
20                             int res = person1.getAge() - t1.getAge();
21                             // 前面减去后面,升序排列
22                             if (res == 0) {
23                                 return person1.getName().charAt(0) - t1.getName().charAt(0);
24                             }
25                             return res;
26                         }
27                     });
28  *
29  * */
30 public class Demo03SortComparator {
31     public static void main(String[] args) {
32         ArrayList<Person1> objects = new ArrayList<>();
33         objects.add(new Person1("b小明", 23));
34         objects.add(new Person1("小红", 24));
35         objects.add(new Person1("小绿", 22));
36         objects.add(new Person1("a小绿", 23));
37 
38         System.out.println("objects = " + objects);
39         Collections.sort(objects, new Comparator<Person1>() {
40             @Override
41             public int compare(Person1 person1, Person1 t1) {
42 //                return 0;
43                 int res = person1.getAge() - t1.getAge();
44 
45                 // 前面减去后面,升序排列
46                 if (res == 0) {
47                     return person1.getName().charAt(0) - t1.getName().charAt(0);
48                 }
49                 return res;
50             }
51         });
52         System.out.println("objects = " + objects);
53     }
54 }
55 
56 
57 class Person1 {
58     private String name;
59     private int age;
60 
61 
62     @Override
63     public String toString() {
64         return "Person{" +
65                 "name=‘" + name + ‘‘‘ +
66                 ", age=" + age +
67                 ‘}‘;
68     }
69 
70     public Person1() {
71     }
72 
73     public Person1(String name, int age) {
74         this.name = name;
75         this.age = age;
76     }
77 
78     public String getName() {
79         return name;
80     }
81 
82     public void setName(String name) {
83         this.name = name;
84     }
85 
86     public int getAge() {
87         return age;
88     }
89 
90     public void setAge(int age) {
91         this.age = age;
92     }
93 }

Comparator

 

 1  * Comparable: 我们的类继承Comparable接口,然后实现里面的CompareTo方法,
 2  *             如何调用:Collections.sort(arrayList)
 3  *
 4  * Comparator: 我们的类不用继承Comparable接口,也不用继承Comparator接口
 5  *             如何调用:Collections.sort(objects, new Comparator<Person1>() {  // 匿名类
 6                         @Override
 7                         public int compare(Person1 person1, Person1 t1) {
 8                             int res = person1.getAge() - t1.getAge();
 9                             // 前面减去后面,升序排列
10                             if (res == 0) {
11                                 return person1.getName().charAt(0) - t1.getName().charAt(0);
12                             }
13                             return res;
14                         }
15                     });