A comment on Using exceptions when designing an API:
When designing an API I use the "get vs find rule." The API's user needs to know how to handle the absence of a result. A get is expected to always return a result while a find is not. And so when coding "getX()" it returns the result or throws an exception -- such as IllegalStateException -- if there is not one. Where as, when coding "findX()" it returns a result if available or a null, or an empty collection, if there not one.