Usually this is not what you want to separate interfaces from implementations. For example, this: List<T> l = new ArrayList<T>(); is preferred to this:

Usually this is not what you want to separate interfaces from implementations. For example, this: List<T> l = new ArrayList<T>(); is preferred to this: ArrayList<T> l = new ArrayList<T>(); Of course, it would be nice for the compiler to assume the latter if no type is specified on the left side.