欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页  >  IT编程

180217_JAVA学习_TreeSet中存放含多个String的类并设置排序规则

程序员文章站 2022-09-28 20:33:53
有Person类如下: 有main如下: 由于TreeSet为可排序集合,所以要为存放对象(Person)指定排序规则。 排序规则:ASC(升序),age > address > name故重写Person的compareTo(): 注:若要DESC排序: 1、age比较中交换1/-1; 2、add ......

有Person类如下:

1 class Person {
2   String name;
3   int age;
4   String address;
5 }

有main如下:

 1 import java.util.TreeSet;
 2 
 3 public class Test{
 4   public static void main(String[] args){
 5     Person p1 = new Person("AA",18,"CN");
 6     Person p2 = new Person("BB",18,"JP");
 7     Person p3 = new Person("CC",18,"CN");
 8 
 9     TreeSet<Person> persons = new TreeSet<>();
10     persons.add(p1);
11     persons.add(p2);
12     persons.add(p3);
13     for (Object person : persons) {
14       System.out.println(person);
15     }
16   }
17 }

由于TreeSet为可排序集合,所以要为存放对象(Person)指定排序规则。

排序规则:ASC(升序),age > address > name
故重写Person的compareTo():

 1 public int compareTo(Person o) {
 2     if(this.age > o.age){
 3         return 1;
 4     }else if(this.age < o.age) {
 5         return -1;
 6     }
 7     //判断age谁大,若相等,则判断address
 8     int x = this.address.compareTo(o.address);
 9     if(x != 0){
10         return x;
11     }
12     //判断address谁大,若相等,则判断name
13     return this.name.compareTo(o.name);
14 }

注:若要DESC排序:

  1、age比较中交换1/-1;
  2、address比较中return相反数值;
  3、name比较中return相反数值;

上述代码的逻辑顺序:
  传入比较对象o与自身进行对比;
    若this.age > o.age,返回“1”;
    若this.age < o.age,返回“-1”;
    若相等,比较address;
  令x = this.address.compareTo(o.address);
    若x != 0,即不相等,x即为要返回的值(1/-1);
    若x == 0,即相等,比较name;
  this.name.compareTo(o.name)的值即为要返回的值:
    若值为 1,即大于,
    若值为-1,即为小于,
    若值为 0,即三处均相等,则完全相等,不应存入。

 

完整代码:

 1 package toBKY;
 2 
 3 import java.util.TreeSet;
 4 
 5 public class Test{
 6     public static void main(String[] args){
 7         Person p1 = new Person("AA",18,"CN");
 8         Person p2 = new Person("BB",18,"JP");
 9         Person p3 = new Person("CC",18,"CN");
10 
11         TreeSet<Person> persons = new TreeSet<>();
12         persons.add(p1);
13         persons.add(p2);
14         persons.add(p3);
15 
16         for (Object person : persons) {
17             System.out.println(person);
18         }
19         //使用for each 比Iterator代码量少
20 
21     }
22 }
23 
24 class Person implements Comparable<Person>{
25     String name;
26     int age;
27     String address;
28 
29     public Person(String name, int age, String address) {
30         this.name = name;
31         this.age = age;
32         this.address = address;
33     }
34 
35     @Override
36     public String toString() {
37         return "Person{" +
38             "name='" + name + '\'' +
39             ", age=" + age +
40             ", address='" + address + '\'' +
41          '}';
42   }
43 
44   @Override
45   public int compareTo(Person o) {
46     if(this.age > o.age){
47       return 1;
48     }else if(this.age < o.age) {
49       return -1;
50     }
51     //判断age谁大,若相等,则判断address
52     int x = this.address.compareTo(o.address);
53     if(x != 0){
54       return x;
55     }
56     //判断address谁大,若相等,则判断name
57     return this.name.compareTo(o.name);
58   }
59 }