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:



/**
* 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:


/**

* 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。


原文链接:https://blog.csdn.net/zxy_snow/article/details/7232035

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