The types are there.. but you don't know which one it is that your program is dealing with. You could have dozens of implementations for any given abstract interface. One gets picked up at run time.
That's the theory. Works great when there are no bugs and everything's been designed just right. In that world you could wipe implementations from memory because you won't ever need to dive in..
Very often I'm looking at code and "how to use the interface" is not a question I'm looking to find answers for.
