How to make a Collection out of a Collection?

Question

I don't want to get into the specifics of my problem since I don't think they are needed.
Anyways, Say I have a Collection of ArrayLists and I want to create a Collection of their size()'s - how would I do that? I found a way to do it but its very messy:
// Assuming lists is a Collection of ArrayLists
Iterator i = lists.iterator();
HashMap tempMap = new HashMap();
// loop through each ArrayList
while( i.hasNext() ) {
     ArrayList currentList = (ArrayList) i.next();
// Add the ArrayList as the key and the size as the value (in Integer form)
// I suppose that anything would work for the keys as long as they are unique
     tempMap.put( currentList, new Integer (currentList.size() ) );
// returns a Collection of size()'s for the ArrayLists
return tempMap.values();Hope I was clear enough - its difficult to describe my problem. I just would like an easier way to do this.
Thanks ;)

Answer 1

There isn't really an easier way. You could use
another array list rather than a hashmap in your
construction.
But at the end of the day, you have to iterate
through all your items, call get size and add them to
your list
Collection listSizes = new ArrayList();
for (Iterator it = lists.iterator; it.hasNext(); ){
Collection c = (Collection)it.next();
c.add(new Integer(c.size()));
return listSizes;
Neanderthals.
Collection<Integer> listSizes = new ArrayList<Integer>();
for (Collection c : lists)
  listSizes.add(c.size());
return listSizes;