How do i get the Iterator size without looping?

Question

How do I get the Iterator size without looping ? Is there anyway to do this ?

Iterator<String> keys = Map.keySet().iterator();

Now I want the size of Keys just forget the Map.keySet() here.

Answer 1

An Iterator just give you a method of walking over a Collection, so the "size of the Iterator" is the size of the collection it iterates over. In this case just use Set's (or any other Collection) built in size() method :

int size = Map.keySet().size();

If you are in a situation where you just have access to the Iterator but need the underlying Collection's size I think you'll need to talk to the one giving you just that iterator, and either get access to the Collection, or get the size of the Collection.

Answer 2

An iterator is an implementation of java.util.Iterator interface. This interface does not provide any method to know the size of it's implementations (In fact these implementations don't need to have a size property). If you need an Iterator with a size, and a method to get it, you should build your own implementation.

However, if what you need is the size of the collection the iterator traverses, fvu answer is correct.