Java，如何使用 compareTo 对 Arraylist 进行排序

Java, how to use compareTo to sort an Arraylist

提问by user3712130

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

我试图弄清楚如何使用可比较对 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;
            }

        }

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?

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？

回答by Makoto

Don't use a raw type with Comparable. Instead, use Comparable<Players>. This way, you have direct access to the object you care about without having to cast from Object.

不要将原始类型与Comparable. 相反，使用Comparable<Players>. 这样，您就可以直接访问您关心的对象，而无需从Object.

The sample compareTowould be this:

样本compareTo是这样的：

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

Then, you would actually have to...sort it, using Collections.sort().

然后，您实际上必须...对其进行排序，使用Collections.sort().

Collections.sort(list);

The reason for Comparable<Players>is that Comparableitself is defined as taking a generic type T.

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

回答by janos

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

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());
    }
}

After all, Playerhas 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 Playerclass does only one thing, encapsulates player data. Instead of adding one more responsibility (sorting), it's better to move that logic in another class.

毕竟，Player有多个字段，很容易想象有时您可能想要对玩家进行不同的排序。这种方法的一大优点是单一职责原则：一个Player类只做一件事，封装玩家数据。与其添加更多职责（排序），不如将该逻辑移到另一个类中。

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

您可以将这些比较器与 一起使用Collections.sort，例如：

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

Extra tips

额外提示

Your class seems to be named Players. It's better to rename to Player.

你的班级似乎被命名为Players。最好重命名为Player.

The getName, getRating, getPosmethods should not return voidand print the result, but return the field values instead.

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。

Use better names for the constructor arguments, for example:

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;
}

Use the right type of list to store players:

使用正确类型的列表来存储玩家：

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

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

请正确格式化您的代码。任何 IDE 都可以做到这一点。

Suggested implementation

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);
    }
}

回答by FruitDealer

Try this.

尝试这个。

public class Comparator_Test {

public static void main(String[] args) {
    ArrayList<Players> list = new ArrayList<Players>();      

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

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

    PlayerComparator comparator = new PlayerComparator();
    System.out.println(list);
    Collections.sort(list, comparator);
    System.out.println(list);
}

}

class Players {

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);
            }

     public String toString() {
         return rating + "";
     }
}

class PlayerComparator implements Comparator<Players> {

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

}