How do I print out an ArrayList<Integer> from a HashSet<ArrayList<Integer>>?

Question

I have a HashSet<ArrayList<Integer>> . Its printed format is:

[ [1, 2], [11, 22], [111, 222] ]

Now, if I just want to print out the last Array<Integer> which is [111, 222] , how do I do that? Is there any similar method to indexOf() for a HashSet ?

Answer 1

You can't as there is no order inside a Set, and therefore no index. So your "last" element is not always the same. If you need them to be in order you could use a LinkedHashSet .

Or you iterate over all elements of the Set and find the one you want to print like that.

Answer 2

Elements in a HashSet aren't stored in any defined order. So asking fo the "last" element of a HashSet doesn't make sense.

If you need an ordered set, then use a LinkedHashSet.

If you need a sorted set, then use a TreeSet.

Answer 3

HashSet does not maintain order, so you will not be able to use API such as indexOf() with HashSet . You need to use List in place of Set to get the indexOf() last element.

    List<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();
    // Add elements in the list

    list .indexOf(list.size()-1); // This will fetch you the last element

Answer 4

No, but you can iterate to the last element and print it:

Iterator i = set.iterator();
List last = null;
while(i.hasNext()) 
   last = i.next();
...

Or you can transform the set into a list and get the last element:

List list = new ArrayList(set);
List last = list.get(list.size() - 1);
...

Answer 5

You can iterate till the last element and print only the last one.

Best way would be if you use TreeSet instead of HashSet.