集合(放对象)排序

用collections.sort方法对list排序有两种方法 
第一种是list中的对象实现comparable接口，如下： 
[java] view plain copy 
/** 
* 根据order对user排序 
*/  
public class user implements comparable{  
     private string name;  
     private integer order;  
     public string getname() {  
         return name;  
     }  
     public void setname(string name) {  
         this.name = name;  
     }  
     public integer getorder() {  
         return order;  
     }  
     public void setorder(integer order) {  
         this.order = order;  
     }  
     public int compareto(user arg0) {  
         return this.getorder().compareto(arg0.getorder());  
     }  
} 测试一下：  
public class test{  
  
     public static void main(string[] args) {  
         user user1 = new user();  
         user1.setname("a");  
         user1.setorder(1);  
         user user2 = new user();  
         user2.setname("b");  
         user2.setorder(2);  
         list list = new arraylist();  
         //此处add user2再add user1  
         list.add(user2);  
         list.add(user1);  
         collections.sort(list);  
         for(user u : list){  
             system.out.println(u.getname());  
         }  
     }  
}   



输出结果如下 
a 
b 
第二种方法是根据collections.sort重载方法来实现，例如： 
[java] view plain copy 
/** 
* 根据order对user排序 
*/  
public class user { //此处无需实现comparable接口  
    private string name;  
     private integer order;  
     public string getname() {  
         return name;  
     }  
     public void setname(string name) {  
         this.name = name;  
     }  
     public integer getorder() {  
         return order;  
     }  
     public void setorder(integer order) {  
         this.order = order;  
     }  
}  
  
主类中这样写即可(hastset——>list——>sort进行排序)：  
public class test {  
    public static void main(string[] args) {  
        user user1 = new user();  
        user1.setname("a");  
        user1.setprice(11);  
        user user2 = new user();  
        user2.setname("b");  
        user2.setprice(2);  
  
        set hset = new hashset();  
        hset.add(user2);  
        hset.add(user1);  
  
        list list = new arraylist();  
        list.addall(hset);  
  
  
        collections.sort(list,new comparator(){  
            public int compare(user arg0, user arg1) {  
                return arg0.getprice().compareto(arg1.getprice());  
            }  
        });  
        for(user u : list){  
            system.out.println(u.getname());  
        }  
    }  


输出结果如下： 
a 
b 

默认为升序，将。return arg0.getorder().compareto(arg1.getorder());    改为： 
return arg1.getorder().compareto(arg0.getorder());   
就成降序的了。