How to sort an arraylist of objects by a property?

Question

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?

Answer 1

Write a custom Comparator to do the job.

Answer 2

Use a generic Comparator like the Bean Comparator.

Answer 3

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

Answer 4

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;
        }

    });

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.

See also

• Java: What is the difference between implementing Comparable and Comparator?

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For completeness, I should caution that the return o1.f - o2.f comparison-by-subtraction shortcut must be used with extreme caution due to possible overflows (read: Effective Java 2nd Edition: Item 12: Consider implementing Comparable). Presumably hockey isn't a sport where a player can score goals in the amount that would cause problems =)

See also

• Java Integer: what is faster comparison or subtraction?