Java List Collections排序

用Collections.sort方法對list排序有兩種方法
第一種是list中的對象實現Comparable接口，如下：

/**
* 根據order對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());
    }
} 測試一下：
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>();
        //此處add user2再add user1
       list.add(user2);
        list.add(user1);
        Collections.sort(list);
        for(User u : list){
            System.out.println(u.getName());
        }
    }
}

輸出結果如下
a
b

第二種方法
根據Collections.sort重載方法來實現，例如：

 //根據order對User排序

public class User { //此處無需實現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;
     }
 }
 
 主類中這樣寫即可(HastSet——>List——>sort進行排序)：
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());
        }
    }

輸出結果如下：

a
b

默認爲升序，將。return arg0.getOrder().compareTo(arg1.getOrder()); 改爲：
return arg1.getOrder().compareTo(arg0.getOrder());
就成降序的了。

轉至：https://blog.csdn.net/zxy_snow/article/details/7232035