自己定义需要比较的东西

 1 public class Bokeyuan {
 2     public static class Student{
 3         public String name;
 4         public int id;
 5         public int age;
 6     
 7     public Student (String name,int id,int age) {
 8         this.name=name;
 9         this.id=id;
10         this.age=age;
11     }
12     }
13     
14     public static class IdAscendingComparator implements Comparator<Student>{//1.Id...自己定义的比较器；2.Comparator  继承接口，接口内放置自己定义的想要比较的东西；3.把定义好的类放到main函数的调用类上
15 
16         @Override
17         public int compare(Student arg0, Student arg1) {
18             // TODO 自动生成的方法存根
19             return arg0.id-arg1.id;//怎么比较？？？1.当返回的数值为负数，前面的数值更小；2.返回的为正数，后面的参数更小，3.返回的为0，相等
20         }        
21     }
22     public static class IdDescendingComparator implements Comparator<Student>{
23 
24         @Override
25         public int compare(Student arg0, Student arg1) {
26             // TODO 自动生成的方法存根
27             return arg1.id-arg0.id;//降序
28         }    
29     }
30     public static class AgeScendingComparator implements Comparator<Student>{
31 
32         @Override
33         public int compare(Student arg0, Student arg1) {
34             // TODO 自动生成的方法存根
35             return arg0.age-arg1.age;//升序
36         }        
37     }
38     public static class AgeDescendingComparator implements Comparator<Student>{
39 
40         @Override
41         public int compare(Student arg0, Student arg1) {
42             // TODO 自动生成的方法存根
43             return arg1.age-arg0.age;//降序
44         }        
45     }
46     public static void printStudent (Student[] students) {
47         for(Student student:students) {//输出函数
48             System.out.println("Name: "+student.name+",Id: "+student.id+",Age:"+student.age);
49             System.out.println("=====================================");
50         }    
51     }
52 
53     public static void main (String[] args) {
54         Student student1 =new Student("A",1,25);
55         Student student2 =new Student("B",2,23);
56         Student student3 =new Student("C",3,24);
57         //建立数组，把学生1，2，3放进去
58         Student[] students =new Student[] {
59             student3,student2,student1
60         };
61         //Arrays.sort调用系统函数   有意义的情况：1.数组2.写入自己定义的比较器，不写的话，是单纯调用sort（students）按照内存地址排序毫无意义。例如，基础类型按照数值大小排序，从小到大。
62         printStudent(students);
63         Arrays.sort(students,new IdAscendingComparator());
64         
65         printStudent(students);
66         Arrays.sort(students,new IdDescendingComparator());
67         
68         printStudent(students);
69         Arrays.sort(students,new    AgeDescendingComparator());
70         
71         printStudent(students);
72         Arrays.sort(students,new AgeScendingComparator());
73         
74             }
75     }