java sort list of objects by specifiable attribute

Question

I want to sort a List of objects by a specified attribute of those objects and I want to choose which attribute should be used for sorting. Example:

class          


        

Answer 1

TL;DR: There's already a wheel for that.

I would say the easiest way to do this is to create a comparator:

final Comparator byName = Comparator.comparing(Car::name);
final Comparator byColour = Comparator.comparing(Car::colour);

Then just use the appropriate method on Arrays to sort by a comparator:

Arrays.sort(carArray, byName);

Now you want to do it with an enum? Just have the enum implements Comparator:

enum SortBy implements Comparator {
    NAME(Comparator.comparing(Car::name)),
    COLOUR(Comparator.comparing(Car::colour));

    private final Comparator delegate;

    private SortBy(Comparator delegate) {
        this.delegate = delegate;
    }

    @Override
    public int compare(final Car o1, final Car o2) {
        return delegate.compare(o1, o2);
    }               
}

Want to sort by name then by colour? Easy:

final Comparator byName = SortBy.NAME.thenComparing(SortBy.COLOUR);

Want to sort by name in reverse order? Easy:

final Comparator byName = SortBy.NAME.reversed();