How to sort an arraylist of objects by a property?

问题

Lets say you have an Arraylist of HockeyPlayer objects.

How could you sort that if they all have a variable int goalsScored. How could you sort them by goalsScored?

回答1:

You can use Collections.sort with a custom 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
        }

    });

The comparision part can also be written this way :

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

Alternatively, you can make HockeyPlayer implementsComparable<HockeyPlayer>. This defines the natural ordering for all HockeyPlayer objects. Using a Comparator is more flexible in that different implementations can order by name, age, etc.

回答2:

As @user6158055 suggets, it's one liner with Java 8, as follows:

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

Complete example to depict the same:

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 + "]";
        }

    }
}

Output:

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]

回答3:

Write a custom Comparator to do the job.

回答4:

Just one line with Java 8 :

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

回答5:

Use a generic Comparator like the Bean Comparator.

回答6:

Java has a set of sort() methods for this sort of thing. See Collections.sort (and Comparable) for details.

回答7:

With Java 8 this is simple

Collections.sort(playList, Comparator.comparingInt(HockeyPLayer::goalsScored))

来源：https://stackoverflow.com/questions/2535124/how-to-sort-an-arraylist-of-objects-by-a-property

标签

java

sorting

collections