Use of generics

[philipa]

The current API does not support polymorphic access to elements - it expects them all to be an E.

Using generics with containers breaks down a little due to Java's limited type model, but I suspect some methods could be relaxed to take INode<? extends E>, and provide INode<? super E>, supporting operations between trees with related but different types.

Also, it would be nice to be able to create an IWalker that is restricted to visiting nodes of type .

[mattunderscorechampion]

I agree more work is needed on the type signatures and generic parameters