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。