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式对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,但我不知道怎么会有人帮助我？

Answer 1

而不是使的Player实现Comparable,你会得到通过实现更大的灵活性Comparator<Player>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有多个领域,很容易想象有时你可能想要以不同的方式订购玩家.这种方法的一个很大的优点是单一责任原则:一个Player类只做一件事,封装了玩家数据.而不是再增加一个责任(排序),最好将该逻辑移到另一个类中.

您可以使用这些比较器Collections.sort,例如:

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

额外提示

你的班级似乎被命名了Players.重命名为最好Player.

的getName,getRating,getPos方法不应返回void打印出结果,但返回的字段值来代替.

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.

建议实施

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);
    }
}

Answer 2

不要使用原始类型Comparable.相反,使用Comparable<Players>.这样,您可以直接访问您关心的对象,而无需进行强制转换Object.

样本compareTo是这样的:

public int compareTo(Player other) {
    return rating - other.getRating();
}

那么,你实际上必须......使用它来排序Collections.sort().

Collections.sort(list);

原因Comparable<Players>是它Comparable本身被定义为采用泛型类型T.