如何按属性对对象的数组列表进行排序？

sorting collections java

2022-09-01 03:29:05

假设您有一个对象。ArraylistHockeyPlayer

如果他们都有一个可变的int进球得分，你怎么能排序呢？您如何按进球得分对它们进行排序？

答案 1

您可以将 Collections.sort 与自定义 Comparator<HockeyPlayer>。

    class HockeyPlayer {
        public final int goalsScored;
        // ...
    };

    List<HockeyPlayer> players = // ...

    Collections.sort(players, new Comparator<HockeyPlayer>() {
        @Override public int compare(HockeyPlayer p1, HockeyPlayer p2) {
            return p1.goalsScored - p2.goalsScored; // Ascending
        }

    });

比较部分也可以这样写：

players.sort(Comparator.comparingInt(HockeyPLayer::goalsScored));

或者，您可以制作Compeable<HockeyPlayer>。这定义了所有对象的自然排序。使用更灵活，因为不同的实现可以按名称、年龄等排序。HockeyPlayer implementsHockeyPlayerComparator

另请参见

Java：实现Compeable和Compolart有什么区别？

为了完整起见，我应该提醒一下，由于可能存在溢出，必须极其谨慎地使用逐减比较快捷方式（阅读：有效的Java第2版：第12项：考虑实现可比较）。据推测，曲棍球不是一项球员可以进球的运动，其进球数量会导致问题=）return o1.f - o2.f

另请参见

Java Integer：什么是更快的比较或减法？

答案 2

作为@user6158055 suggets，它是一个带有的衬里，如下所示：Java 8

Collections.sort(
                hockeyPlayerList,
                (player1, player2) -> player1.getGoalsScored()
                        - player2.getGoalsScored());

完整的示例来描述相同的内容：

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

public class Main {

    public static void main(String[] args) {
        List<HockeyPlayer> hockeyPlayerList = new ArrayList<>();
        hockeyPlayerList.add(new HockeyPlayer("A", 3));
        hockeyPlayerList.add(new HockeyPlayer("D", 10));
        hockeyPlayerList.add(new HockeyPlayer("B", 2));

        System.out.println("Before Sort based on goalsScored\n");

        hockeyPlayerList.forEach(System.out::println);

        System.out.println("\nAfter Sort based on goalsScored\n");

        Collections.sort(
                hockeyPlayerList,
                (player1, player2) -> player1.getGoalsScored()
                        - player2.getGoalsScored());

        hockeyPlayerList.forEach(System.out::println);
    }

    static class HockeyPlayer {

        private String name;
        private int goalsScored;

        public HockeyPlayer(final String name, final int goalsScored) {
            this.name = name;
            this.goalsScored = goalsScored;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public int getGoalsScored() {
            return goalsScored;
        }

        public void setGoalsScored(int goalsScored) {
            this.goalsScored = goalsScored;
        }

        @Override
        public String toString() {
            return "HockeyPlayer [name=" + name + ", goalsScored="
                    + goalsScored + "]";
        }

    }
}

输出：

Before Sort based on goalsScored

HockeyPlayer [name=A, goalsScored=3]
HockeyPlayer [name=D, goalsScored=10]
HockeyPlayer [name=B, goalsScored=2]

After Sort based on goalsScored

HockeyPlayer [name=B, goalsScored=2]
HockeyPlayer [name=A, goalsScored=3]
HockeyPlayer [name=D, goalsScored=10]