Java: Get first item from a collection
If I have a collection, such as Collection<String> strs, how can I get the first item out? I could just call an Iterator, take its first next(), then throw the Iterator away. Is there a less wasteful way to do it?
Answer
Looks like that is the best way to do it:
String first = strs.iterator().next();
Great question... At first, it seems like an oversight for the Collection interface.
Note that "first" won't always return the first thing you put in the collection, and may only make sense for ordered collections. Maybe that is why there isn't a get(item) call, since the order isn't necessarily preserved.
While it might seem a bit wasteful, it might not be as bad as you think. The Iterator really just contains indexing information into the collection, not a usually a copy of the entire collection. Invoking this method does instantiate the Iterator object, but that is really the only overhead (not like copying all the elements).
For example, looking at the type returned by the ArrayList<String>.iterator() method, we see that it is ArrayList::Itr. This is an internal class that just accesses the elements of the list directly, rather than copying them.
Just be sure you check the return of iterator() since it may be empty or null depending on the implementation.