Suppose you have a collection, and you need to perform an action on each element. That's not hard to do in any mainstream programming language. What if you need to know the index of each element as you process it? Not hard, but depending on your datastructures, possibly not as straightforward as it first sounds.

When Eclipse Juno came out last year, I was excited to see some support for `@Nullable` annotations. I didn't get very far with them at the time, though, as the implementation was quite strict. With the release of Kepler though, it's much easer to make productive use of `@Nullable` to help avoid errors.