Java，如何使用compareTo對Arraylist進行排序

Question

我試圖弄清楚如何使用可比較的方式對ArrayList進行排序，我的代碼如下所示：

 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;
            }

        }

我想根據屬性評級對Arraylist進行排序。 我想我應該使用compareTo函數，但我不知道怎么會有人幫助我？

Answer 1

通過實現Comparator<Player>類，您可以獲得更大的靈活性，而不是讓Player實現Comparable 。 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());
    }
}

畢竟， Player有多個領域，很容易想象有時你可能想要以不同的方式訂購玩家。 這種方法的一大優勢是單一責任原則 ： Player類只做一件事，封裝了玩家數據。 而不是再增加一個責任（排序），最好將該邏輯移到另一個類中。

您可以將這些比較器與Collections.sort ，例如：

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

額外提示

你的班級似乎被命名為Players 。 最好重命名為Player 。

getName ， getRating ， getPos方法不應返回void並打印結果，而是返回字段值。

為構造函數參數使用更好的名稱，例如：

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

使用正確類型的列表來存儲玩家：

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

請正確格式化您的代碼。 任何IDE都可以做到這一點。

建議實施

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

不要將原始類型與Comparable 。 相反，請使用Comparable<Players> 。 這樣，您可以直接訪問您關注的對象，而無需從Object 。

樣本compareTo將是這樣的：

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

然后，您實際上必須使用Collections.sort()對其進行排序。

Collections.sort(list);

Comparable<Players>的原因是Comparable本身被定義為采用泛型類型T

Answer 3

嘗試這個。

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;
}

}