集合-TreeSet-Comparable

Posted 2020-09-18

Student类：name、age属性 
1 package com.bjpowernode.test01_set2_Comparable;
 2 /*
 3  * T: type
 4  */
 5 public class Student implements Comparable<Student> {
 6     private String name;
 7     private int age;
 8     public String getName() {
 9         return name;
10     }
11     public void setName(String name) {
12         this.name = name;
13     }
14     public int getAge() {
15         return age;
16     }
17     public void setAge(int age) {
18         this.age = age;
19     }
20     public Student(String name, int age) {
21         super();
22         this.name = name;
23         this.age = age;
24     }
25     public Student() {
26         super();
27         // TODO Auto-generated constructor stub
28     }
29     /*@Override
30     public int hashCode() {
31         final int prime = 31;
32         int result = 1;
33         result = prime * result + age;
34         result = prime * result + ((name == null) ? 0 : name.hashCode());
35         return result;
36     }
37     @Override
38     public boolean equals(Object obj) {
39         if (this == obj)
40             return true;
41         if (obj == null)
42             return false;
43         if (getClass() != obj.getClass())//判断两个“对象”的类型是否相同。
44             return false;
45         Student other = (Student) obj; //向下转型 
46         if (age != other.age)
47             return false;
48         if (name == null) {  //避免出现NullPointerException异常
49             if (other.name != null)
50                 return false;
51         } else if (!name.equals(other.name))
52             return false;
53         return true;
54     }*/
55     /*
56      * 当前对象与参数对象相同时返回 ： 0
57      * 当前对象 大于参数对象 时： 1  正数
58      *  当前对象 小于参数对象 时： -1 负数
59      */
60     @Override
61     public int compareTo(Student s) {
62         //按年龄排序，如果年龄相同，按姓名排序
63         if(this.age == s.age){
64             //按姓名排序， 调用字符串的compareTo
65             return this.name.compareTo(s.name);
66         }
67         return this.age -s.age;
68     }
69     
70 }

 TreeSet存储，遍历，排序输出
 1 package com.bjpowernode.test01_set2_Comparable;
 2 
 3 import java.util.TreeSet;
 4 /*
 5  * TreeSet中存放元素，默认按自然排序的方式去除重复项，并进行排序的
 6  * String和8种包装类中都指定自然排序方法：实现java.lang.Comparable接口，重写compareTo方法
 7  * 自定义的类放入TreeSet时，也实现实现java.lang.Comparable接口，重写compareTo方法
 8  */
 9 public class StudentTreeSetTest {
10     public static void main(String[] args) {
11         TreeSet<Student> tree = new TreeSet<>();
12         Student s = new Student("Mike", 18);
13         Student s1 = new Student("Join", 28);
14         Student s3 = new Student("Join", 18);
15         Student s4 = new Student("Smith", 18);
16         tree.add(s);
17         tree.add(s1);
18         tree.add(s3);
19         tree.add(s4);
20         System.out.println(tree.size());
21         System.out.println("姓名\t年龄");
22         for (Student stu : tree) {
23             System.out.println(stu.getName()+"\t"+stu.getAge());
24         }
25     }
26 }