如何对对象的 Arraylist 进行排序 [英] How to sort Arraylist of objects

问题描述

我有 ArrayList，它包含足球队(班级 Team).团队有积分，我想按积分对它们进行排序.

I have ArrayList, which containst football teams (class Team). Teams have points and i want to sort them by number of points.

 public class Team {
     private int points;
     private String name;

     public Team(String n)
     {
         name = n;
     }

     public int getPoints
     {
         return points;
     }

     public void addPoints(boolean win)
 {
            if (win==true)
            {
    points = points + 3;
            }

            else if (win==false)
            {
            points = points + 1;
            }

}
 //...
 }

主类:

 List<Team> lteams = new ArrayList<Team>;

 lteams.add(new Team("FC Barcelona"));
 lteams.add(new Team("Arsenal FC"));
 lteams.add(new Team("Chelsea"));

 //then adding 3 points to Chelsea and 1 point to Arsenal

 lteams.get(2).addPoints(true);
 lteams.get(1).addPoints(false);

 //And want sort teams by points (first index with most points). 

我做了我的比较器.

 public class MyComparator implements Comparator<Team> {


    @Override
    public int compare(Team o1, Team o2) {
        if (o1.getPoints() > o2.getPoints())
         {
             return 1;
         }
        else if (o1.getPoints() < o2.getPoints())
        {
            return -1;
        }
        return 0;    
    } 

}

现在我想使用它(在主类中)

now I wanna use it (in main class)

 Colections.sort(lteams, new MyComparator());

我想看:

1. 切尔西
2. 阿森纳
3. 巴塞罗那

但它没有排序.

推荐答案

来源:这里

您可以使用 Collections.sort 带有自定义 比较器<团队>.

You can use Collections.sort with a custom Comparator<Team>.

    class Team {
        public final int points;
        // ...
    };

    List<Team> players = // ...

    Collections.sort(players, new Comparator<Team>() {
        @Override public int compare(Team p1, Team p2) {
            return p1.points- p2.points;
        }

    });

或者，您可以使团队实现可比<团队>.这定义了所有Team 对象的 自然顺序.使用 Comparator 更加灵活，因为不同的实现可以按名称、年龄等排序.

Alternatively, you can make Team implementsComparable<Team>. This defines the natural ordering for all Team objects. Using a Comparator is more flexible in that different implementations can order by name, age, etc.

• Java:实现Comparable 和 Comparator?

为了完整起见，我应该注意 return o1.f - o2.f 比较减法快捷方式必须非常谨慎，因为可能会溢出(阅读:Effective Java第二版:第 12 项:考虑实现 Comparable).大概曲棍球不是一项运动，其中球员可以进球的数量会导致问题=)

For completeness, I should caution that the return o1.f - o2.f comparison-by-subtraction shortcut must be used with extreme caution due to possible overflows (read: Effective Java 2nd Edition: Item 12: Consider implementing Comparable). Presumably hockey isn't a sport where a player can score goals in the amount that would cause problems =)

• Java 整数:什么是更快的比较或减法?

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