Associate an iterator to the collection and get the first and the last elements in the collection..
U may need to typecast the object when retrieving the element
Joined: Jan 09, 2003
I have got iterator but it would iterate one by one. I do not want to write a while loop and break statement for 1st element and for last element to iterate the whole collection through iterator has next.
Is there any other way, as Collectio have size() but do not have any get method to retrieve the element. Any other way around other than this.
Joined: Jan 29, 2003
The loop is one choice, toArray might be another. I wouldn't worry much about the efficiency of the loop unless you have bazillions of entries. Collection doesn't have item(n) or elementAt(n). Some of the implementing classes do, but if you have to work with Collection you can only use Collection methods.
If you have to write this against a Collection rather than List, you have no choice but to iterate (toArray will iterate and allocate an array, so it's possibly more expensive [ArrayList has an array already, so it can use System.arraycopy(), so it won't iterate, but I digress]).
The reason is that Collection is the lowest common denominator of a "thing that holds other objects," and it has no concept of ordering. List provides indexed access, allowing you to call list.get(0) and list.get(list.size()-1).
Note that this implies that Collection itself doesn't have any idea of "first" and "last" elements. In fact, it's conceivable (though unlikely in practice) that getting the first and last elements from a generic Collection could return different elements on subsequent calls.
For example, if I'm holding five coins in my hand, which one is the first one? And after I shake them around in my hand? The collection of coins hasn't changed since they are unordered.