180217_JAVA _ TreeSet stores classes containing multiple strings and sets sorting rules,

180217_JAVA _ TreeSet stores classes containing multiple strings and sets sorting rules,

The Person class is as follows:

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

The main is as follows:

 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 }

Because TreeSet is a sortedset, you must specify a sorting rule for the stored object (Person.

Sorting rules: ASC (ascending), age> address> name
Therefore, rewrite the compareTo () of Person ():

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 // determine the age. If the age is equal, the address 8 int x = this. address. compareTo (o. address); 9 if (x! = 0) {10 return x; 11} 12 // determines who the address is. If it is equal, determine name13 return this. name. compareTo (o. name); 14}

Note: To sort by DESC:

1. Switch 1/-1 in age comparison;
2. return inverse value in address comparison;
3. return inverse value in name comparison;

The logic sequence of the above Code:
Comparison between input comparison object o and itself;
If this. age> o. age, "1" is returned ";
If this. age <o. age, "-1" is returned ";
If equal, compare address;
Make x = this. address. compareTo (o. address );
If x! = 0, that is, not equal, x is the value to be returned (1/-1 );
If x = 0, that is, equal, compare name;
The value of this. name. compareTo (o. name) is the value to be returned:
If the value is 1, that is, greater,
If the value is-1, it is smaller,
If the value is 0, that is, all three are equal, they are completely equal and should not be saved.

 

Complete code:

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 // use for each less than Iterator Code 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 @ Override36 public String toString () {37 return "Person {" + 38 "name = '" + name +' \ ''+ 39 ", age = "+ age + 40", address = '"+ addr Ess + '\ ''+ 41'}'; 42} 43 44 @ Override45 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 // determines who is the age. If the age is equal, the address52 int x = this. address. compareTo (o. address); 53 if (x! = 0) {54 return x; 55} 56 // determines who the address is. If it is equal, determine name57 return this. name. compareTo (o. name); 58} 59}