This develops up in Java 5 and later if you're doing collections without type specifiers (e.g., Arraylist() rather of ArrayList<String>()). It implies that the compiler can't check that you're using the collection in a type-safe way, using generics.
To get rid of the signal, just be particular about what type of objects you're storing in the collection. So, rather of
List myList = new ArrayList();
List<String> myList = new ArrayList<String>();
In Java 7 you can reduce generic instantiation by applying Type Inference.
List<String> myList = new ArrayList<>();