What does he mean by that? Surely the servlet can instantiate some other Java object -that does not implement any interface- to do the work of creating the "Hello World" string for it. Is that what you're asking?
pojo is just a way of separating your bussiness from your application.........so if in future if you want to change the logic you can simply go to your mvc (model view control)
.......and change the logic !!
try to refer HFJS......THAT WILL HELP YOU A LOT....its OVER COOL but fine it have all we ever wanted in a book !!!