【转】java List 排序 Collections.sort

java List 排序 Collections.sort

 

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： 

代码:

/**
* 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());
     }
}



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());
         }
     }
}

<span style="">/**
* 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());
    }
}

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());
        }
    }
}

</span>

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： 

代码:

/**
* 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;
     }
}




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>();
        list.add(user2);
        list.add(user1);
        Collections.sort(list,new Comparator<User>(){
           public int compare(User arg0, User arg1) {
               return arg0.getOrder().compareTo(arg1.getOrder());
            }
        });
       for(User u : list){
           System.out.println(u.getName());
        }
     }
}

最简单的就是上面红色的字。。。。。。。。。。。

默认为升序，将。return arg0.getOrder().compareTo(arg1.getOrder());    改为：

return arg1.getOrder().compareTo(arg0.getOrder());   

就成倒序的了。。