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

I think the solution would be more efficient if you passed a Comparator implementation to the Arrays.sort. Right now, you are looping n*2 from the looks of it, the hash map (O(1)) plus the Arrays.sort (which is another 0(n log n) or such). If you do the below, you could skip the 2 loops, and the map, you are using currently.

You can simply create a Comparator like (rough code):

class CarComparator implements Comparator {
    enum compareType; //plus setter

    public int compareTo(Car a, Car b) {
        if(compareType == COLOUR) return a.colour.compareTo(b.colour);
        if(compareType == NAME.....
    }
}

, and then simply send the array of Cars to

Arrays.sort(cars, new CarComparator(COLOUR))

, or use more specialised comparator classes, one for each attribute, and a factory to render them, and of course don't create a new Comparator() for each sort if this is happening often. :-)

Overall, this approach should make your code more efficient. }