Java，如何使用compareTo对Arraylist进行排序 [英] Java, how to use compareTo to sort an Arraylist

问题描述

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：

Im trying to figure out how to sort an ArrayList using comparable, my code looks like this:

 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;
            }

        }

我想基于Arraylist进行排序关于属性评级。我想我应该使用compareTo函数，但我不知道怎么会有人帮助我？

I want to sort the Arraylist based on the attribute rating. I suppose I should use the compareTo function but I have no idea how, can someone help me?

推荐答案

而不是使播放器实现可比较，通过实施 Comparator< Player> 类，您可以获得更大的灵活性。例如：

Instead of making Player implement Comparable, you get more flexibility by implementing Comparator<Player> classes. For example:

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，播放器有多个字段，很容易想象有时你可能想要以不同方式订购玩家。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。而不是再添加一个责任（排序），最好将该逻辑移到另一个类中。

After all, Player has multiple fields, it's easy to imagine that sometimes you might want to order players differently. A great advantage of this approach is the single responsibility principle: a Player class does only one thing, encapsulates player data. Instead of adding one more responsibility (sorting), it's better to move that logic in another class.

您可以将这些比较器与 Collections.sort一起使用，例如：

You could use these comparators with Collections.sort, for example:

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

额外提示

您的课程似乎被命名为玩家。最好重命名为播放器。

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

The getName, getRating, getPos methods should not return void and print the result, but return the field values instead.

为构造函数参数使用更好的名称，例如：

Use better names for the constructor arguments, for example:

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：

Use the right type of list to store players:

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

请正确格式化您的代码。任何IDE都可以这样做。

Please format your code properly. Any IDE can do that.

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);
    }
}

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