集合(放对象)排序

//转载：http://blog.csdn.net/zxy_snow/article/details/7232035

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<User>{ 
     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<User> list = new ArrayList<User>(); 
         //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<User> Hset = new HashSet<User>(); 
        Hset.add(user2); 
        Hset.add(user1); 
 
        List<User> list = new ArrayList<User>(); 
        list.addAll(Hset); 
 
 
        Collections.sort(list,new Comparator<User>(){ 
            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。