Sort Sets in ArrayList by Size

Question

I thought of doing this by putting all of the sets in a list that would then be in a map, where the key is the size. I know the maximum size that a set could be(given to me), so I can just iterate between 0 and that number, get each list and then iterate through each list and put each set in an arraylist.

However, this seems horrifically clunky - is there a better way of doing this? Is there some way I can do a comparator function based on size?

Thanks

Answer 1

You can provide a Comparator for that. and use Collections.sort()

class SizeComarator implements Comparator<Set<?>> {

    @Override
    public int compare(Set<?> o1, Set<?> o2) {
        return Integer.valueOf(o1.size()).compareTo(o2.size());
    }
}

    ArrayList<Set<String>> arrayList = new ArrayList<Set<String>>();
    Set<String> set1 = new HashSet<String>();
    set1.add("A");
    set1.add("B");
    Set<String> set2 = new HashSet<String>();
    set2.add("A");
    arrayList.add(set1);
    arrayList.add(set2);
    Collections.sort(arrayList, new SizeComarator());
    System.out.println(arrayList);

Output:

 [[A], [A, B]]