import java.util.ArrayList;

import java.util.Collections; import java.util.Comparator;

public class ComparableTest {  public static void main(String[] args) {     Comparator<Student> comparator = new Comparator<Student>(){      public int compare(Student s1, Student s2) {       //先排年龄       if(s1.age!=s2.age){        return s2.age-s1.age;       }       else{        //年龄相同则按姓名排序        if(!s1.name.equals(s2.name)){         return s2.name.compareTo(s1.name);        }        else{         //姓名也相同则按学号排序         return s2.id-s1.id;        }       }      }     };     Student stu1 = new Student (1,"zhangsan","male",28,"cs");     Student stu2 = new Student (2,"lisi","female",19,"cs");     Student stu3 = new Student (3,"wangwu","male",22,"cs");     Student stu4 = new Student (4,"zhaoliu","female",17,"cs");     Student stu5 = new Student (5,"jiaoming","male",22,"cs");

    ArrayList<Student> List = new ArrayList<Student>();

    List.add(stu1);     List.add(stu2);     List.add(stu3);     List.add(stu4);     List.add(stu5);      //这里就会自动根据规则进行排序     Collections.sort(List,comparator);     display(List);    }        static void display(ArrayList<Student> lst){     for(Student s:lst)      System.out.println(s);    }   }

  class Student{

   int age;    int id;    String gender;    String name;    String cs;    Student(int id,String name,String gender,int age,String cs){     this.age=age;     this.name=name;     this.gender=gender;     this.id=id;     this.cs=cs;    }    public String toString(){     return id+"  "+name+"  "+gender+"  "+age+"  "+cs;    }   }

2.添加 Comparable 接口，重写 compareTo 方法。然后你可以用 TreeSet 结构进行排序。它会自动排序。