如何按属性对对象的arylylist进行排序？

Question

比方说你有一个Arraylist的HockeyPlayer对象.

如果他们都有一个变量int goalsScored你怎么能排序.你怎么能按目标排序呢？

Answer 1

您可以使用Collections.sort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,你可以做HockeyPlayer implementsComparable<HockeyPlayer>.这定义了所有HockeyPlayer对象的自然顺序.使用a Comparator更灵活,因为不同的实现可以按名称,年龄等顺序排序.

也可以看看

• Java:实现Comparable和有Comparator什么区别？

为了完整起见,我应该注意,return o1.f - o2.f由于可能的溢出,必须非常谨慎地使用逐个减法的快捷方式(阅读:Effective Java 2nd Edition:Item 12:考虑实现Comparable).据推测,曲棍球并不是一项运动,其中球员可以在引起问题的数量上进球... =)

也可以看看

• Java Integer:什么是更快的比较或减法？

Answer 2

正如@ user6158055所说,它是一个班轮Java 8,如下:

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

描述相同的完整示例:

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]

Answer 3

Java 8 只需一行：

Collections.sort(players, (p1, p2) -> p1.getGoalsScored() - p2.getGoalsScored());

Answer 4

编写一个自定义比较器来完成这项工作。