TreeSets Sets Within Set

Question

I have started implementing a TreeSet in java. i wish to knows, is it possible to create a set within a set.

For example i need to create a set that gives output

{{1,2,3,4,5,6,7,8},(1,{1,2,3,4,5,6,7,8})}

The problem is that i can't get add to my sets to give the desired output. I have even tried putting my treeset within an arraylist.

ArrayList<TreeSet<Integer>> SET = new ArrayList<TreeSet<Integer>>();

this still doesn't give me my desired result, and makes my code really complicated.

as you can see, the output has 2 sets that are basically elements of a larger set.

Please can anyone help?

I AM NOT ASKING FOR CODE ONLY ADVICE!!!

Answer 1

TreeSet<T> needs a comparator on T in order to arrange the elements inside it. You can cerate a TreeSet with a custom comparator that "understands" how to compare TreeSets. This will let the outer tree set decide on the order of the tree sets that you put inside it:

TreeSet<TreeSet<Integer>> outer = new TreeSet<TreeSet<Integer>>(
    new Comparator<TreeSet<Integer>>() {
        public int compare(TreeSet<Integer> lhs, TreeSet<Integer> rhs) {
            Iterator<Integer> li = lhs.Iterator();
            Iterator<Integer> ri = rhs.Iterator();
            while (li.hasNext() && ri.hasNext()) {
                int res = li.next().compareTo(ri.next());
                if (res != 0) return res;
            }
            if (li.hasNext()) return 1;
            if (ri.hasNext()) return -1;
            return 0;
        }
    }
);

Answer 2

Your use of Generics is confusing you.

This: ArrayList<TreeSet<Integer>> SET = new ArrayList<TreeSet<Integer>>();

Doesn't put a list in a list.

To do that you need to do this:

TreeSet s = new TreeSet();
TreeSet subset = new TreeSet();
s.add(subset);