java List 排序 Collections.sort() 對 List 排序

//一個POJO例子

class User {
 String name;
 String age;
 
 public User(String name,String age){
  this.name=name;
  this.age=age;
 }
 public String getAge() {
  return age;
 }
 public void setAge(String age) {
  this.age = age;
 }
 public String getName() {
  return name;
 }
 public void setName(String name) {
  this.name = name;
 } 
}

//具體的比較類，實現Comparator接口

import java.util.Comparator;
import java.util.List;
import java.util.ArrayList;
import java.util.Collections;

public class ComparatorUser implements Comparator{

 public int compare(Object arg0, Object arg1) {
  User user0=(User)arg0;
  User user1=(User)arg1;

   //首先比較年齡，如果年齡相同，則比較名字

  int flag=user0.getAge().compareTo(user1.getAge());
  if(flag==0){
   return user0.getName().compareTo(user1.getName());
  }else{
   return flag;
  }  
 }
 
}

//測試類
public class SortTest {

 
 public static void main(String[] args){
  List userlist=new ArrayList();
  userlist.add(new User("dd","4"));
  userlist.add(new User("aa","1"));
  userlist.add(new User("ee","5"));
  userlist.add(new User("bb","2"));  
  userlist.add(new User("ff","5"));
  userlist.add(new User("cc","3"));
  userlist.add(new User("gg","6"));
  
  ComparatorUser comparator=new ComparatorUser();
  Collections.sort(userlist, comparator);
   
  for (int i=0;i<userlist.size();i++){
   User user_temp=(User)userlist.get(i);
      System.out.println(user_temp.getAge()+","+user_temp.getName()); 
  }
  
 }
}

 //首先年齡排序，如果年齡相同，則按名字排序

結果:
   1, aa
   2, bb
   3, cc
   4, dd
   5, ee                    //注意:同樣是5歲的人，則比較名字(ee,ff)，然后排序
   5, ff
   6, gg