java List 排序 Collections.sort() 对 List 排序

关于Collections.sort(List list,Comparator comparator) 的说明

Comparator是个接口，主要比的是两个对象,比较规则是你自己写的
，可以重写他的compare（）和equals（）这两个方法，也就是说比较的方法，如果是null的话，就是使用元素的自然顺序，如1，2，4，5，9，8，7，就是1，2，4，5，7，8，9这样，字母也可以



compare（a,b）方法:根据第一个参数小于、等于或大于第二个参数分别返回负整数、零或正整数



例：            
            
import java.util.Comparator;            
import java.util.List;            
import java.util.ArrayList;            
import java.util.Collections;            
            
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;            
}             
}            
            
class ComparatorUser implements Comparator{            
            
public int compare(Object arg0, Object arg1) {            
  User user0=(User)arg0;            
  User user1=(User)arg1;            
  //首先比较年龄，如果年龄相同，则比较名字            
  int flag=user0.getAge().compareTo(user1.getAge());            
  if(flag==0){            
   return user0.getName().compareTo(user1.getName());            
  }else{            
   return flag;            
  }              
}            
            
}            
            
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());             
  }            
              
}            
}            
            
//首先比较年龄，如果年龄相同，则比较名字            
            
结果:            
   1, aa            
   2, bb            
   3, cc            
   4, dd            
   5, ee            
   5, ff            
   6, gg