Java，如何使用 compareTo 对 Arraylist 进行排序

Question

我试图弄清楚如何使用可比较的方法对 ArrayList 进行排序，我的代码如下所示:

 public class playerComparsion{

        public static void main(String[] args){ 


    ArrayList<Object> list = new ArrayList<Object>();      

        Player p1 = new Players(1,92,Zlatan);
    Player p2 = new Players(2,92,Hazard);
    Player p3 = new Players(1,82,Klose);

    list.add(p1);
    list.add(p2);
    list.add(p3);
        }
    } 
        class Players implements Comparable{

        int position;
             String name;
            int rating;

            public Players(int i, int j, String string)  {

                this.position=i;
                this.rating=j;
                this.name=string;
            }

             public void getRating() {
                    System.out.println(this.rating);
                    }
             public void getPos() {
                    System.out.println(this.position);
                    }
             public void getName() {
                    System.out.println(this.name);
                    }

            @Override
            public int compareTo(Object o) {
                // TODO Auto-generated method stub
                return 0;
            }

        }

我想根据属性评级对 Arraylist 进行排序。我想我应该使用 compareTo 函数，但我不知道如何使用，有人可以帮助我吗？

Answer 1

而不是制作 Player实现 Comparable ，您可以通过实现 Comparator<Player> 获得更大的灵 active 类。例如:

class PlayerComparatorByRating implements Comparator<Player> {
    @Override
    public int compare(Player o1, Player o2) {
        return o1.getRating() - o2.getRating();
    }
}

class PlayerComparatorByName implements Comparator<Player> {
    @Override
    public int compare(Player o1, Player o2) {
        return o1.getName().compareTo(o2.getName());
    }
}

毕竟，Player有多个字段，很容易想象有时您可能想要以不同的方式对玩家进行排序。这种方法的一大优势是单一职责原则:Player类只做一件事，封装播放器数据。与其再增加一个职责(排序)，不如将该逻辑移到另一个类中。

您可以将这些比较器与 Collections.sort 一起使用，例如:

Collections.sort(list, new PlayerComparatorByRating());
System.out.println(list);
Collections.sort(list, new PlayerComparatorByName());
System.out.println(list);

额外提示

你的类(class)好像叫Players .最好重命名为Player .

getName , getRating , getPos方法不应返回 void并打印结果，但返回字段值。

为构造函数参数使用更好的名称，例如:

Player(int position, int rating, String name) {
    this.position = position;
    this.rating = rating;
    this.name = name;
}

使用正确类型的列表来存储玩家:

List<Player> list = new ArrayList<Player>();

请正确格式化您的代码。任何 IDE 都可以做到这一点。

建议实现

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

class Player {
    private int position;
    private int rating;
    private final String name;

    Player(int position, int rating, String name) {
        this.position = position;
        this.rating = rating;
        this.name = name;
    }

    public int getRating() {
        return rating;
    }

    public int getPos() {
        return position;
    }

    public String getName() {
        return name;
    }

    @Override
    public String toString() {
        return String.format("%s:%d:%d", name, position, rating);
    }
}

class PlayerComparatorByRating implements Comparator<Player> {
    @Override
    public int compare(Player o1, Player o2) {
        return o1.getRating() - o2.getRating();
    }
}

class PlayerComparatorByName implements Comparator<Player> {
    @Override
    public int compare(Player o1, Player o2) {
        return o1.getName().compareTo(o2.getName());
    }
}

public class PlayerComparatorDemo {
    public static void main(String[] args){
        List<Player> list = new ArrayList<Player>();

        Player p1 = new Player(1, 92, "Zlatan");
        Player p2 = new Player(2, 92, "Hazard");
        Player p3 = new Player(1, 82, "Klose");

        list.add(p1);
        list.add(p2);
        list.add(p3);

        Collections.sort(list, new PlayerComparatorByRating());
        System.out.println(list);
        Collections.sort(list, new PlayerComparatorByName());
        System.out.println(list);
    }
}