The desired refresh time, in seconds. After this much time from the previous update, the
refresh() method is called.
the number of seconds between the calls to refresh()
Update the contents of the cache entry. The implementation is application-dependent.
Typically it involves filling an internal hash with some values from the database. But it
can do whatever operation here, even something that doesn't involve actually caching anything,
but just to execute a periodic task (cron style).
The cached entry is most probably a hash of some sort. This is why the get() method
is specified in this interface, to provide an easy and uniform way of retrieving the
data between all the implementations.
key - some unique key
the value associated with that key, if any, or null.