List 中对象属性排序

有几个方法可以实现：让 Student 实现Comparable接口，或是实例化一

个比较器，

现在用 Comparator 比较器实例来做一个：ComparableTest.java

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 s1.age-s2.age;
    }
    else{
     //年龄相同则按姓名排序
     if(!s1.name.equals(s2.name)){
      return s1.name.compareTo(s2.name);
     }
     else{
      //姓名也相同则按学号排序
      return s1.id-s2.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;
}