一段代码，关于compareable接口的使用，不太理解,该怎么处理

import java.util.Set ;import java.util.TreeSet ;class Person implements Comparable<Person>{    private String name ;    private int age ;    public Person(String name,int age){        this.name = name ;        this.age = age ;    }    public String toString(){        return "姓名：" + this.name + "；年龄：" + this.age ;    }    public int compareTo(Person per){        if(this.age>per.age){            return 1 ;        }else if(this.age<per.age){            return -1 ;        }else{            return this.name.compareTo(per.name) ;        }    }};public class test01{    public static void main(String args[]){        Set<Person> allSet = new TreeSet<Person>() ;        allSet.add(new Person("张三",30)) ;        allSet.add(new Person("李四",31)) ;        allSet.add(new Person("王五",32)) ;        allSet.add(new Person("王五",32)) ;        allSet.add(new Person("王五",32)) ;        allSet.add(new Person("赵六",33)) ;        allSet.add(new Person("孙七",33)) ;        System.out.println(allSet) ;    }};

public int compareTo(Person per){        if(this.age>per.age){            return 1 ;        }else if(this.age<per.age){            return -1 ;        }else{            return this.name.compareTo(per.name) ;        }