The KeyedCollection
Use KeyedCollection if you want a List that is continously sorted
Can either have seperate key objects for each member (Map) or treat the members as keys (Set)
Important: You must provide the key object yourself
A key object knows how to respond to a
method call. It then retrieves
the value in obj and responds
with {-1,0,1} depending on
if it is <, equal to, > than obj