| AbstractReaper | Abstract base class all reapers have to extend. |
| NotifyingReaper | Does the obvious: Calls a handleExpiredObject method for each object in the
container. |
| NullReaper | The simplest of all possible expiration handlers. |
| RefreshingReaper | Calls a refresh method on each object in the container; it reinserts any
returned object to the front of the expiration system. |
| ReinsertingReaper | A hybrid of the notifying and refreshing reaper; like the notifying reaper,
this calls handleExpiredObject for the object; like the refreshing reaper, it
then reinserts it in the front of the expiration system. |