RE: nullable pointers

The example was simply to show that you don't need all pointers to be nullable to have linked lists. The advantages for this case are minimal, since linked lists specifically depend on the 'next' pointer being nullable. However, linked lists are a hardly representative of pointers in general, particularly in a language like Java where all objects are accessed via pointers. The benefit of making pointers non-nullable by default is in the majority of cases where nulls are nothing but a source of runtime exceptions.

The advantages tend to be more pronounced in languages like Haskell, however, which have more advanced type systems which handle this sort of subtyping without any need for runtime casts. As you point out, in Java you would need to explicitly cast from List<T> to ListNil<T> or ListCons<T>, an operation which can fail in much the same manner as dereferencing a null pointer.

> Sure, but you still have a specialised nil type. Whether you use a null reference on a List type to denote the end of the list or a special EmptyList class, it still means your code has to take to check what exactly the reference is pointing to before going through it to avoid a runtime exception.
How many times do you want me to repeat this? The fact that you need a way to represent the empty list does not mean that you need nullable pointers _everywhere_, even where they _don't_ have any purpose (unlike the list case).