class ListingCache extends CacheObserver

The rest of the code is Ruby but this isn't. Guessing this code wasn't copied and pasted but written on the fly by someone who's been doing some Java recently? :-)

...Guilty.

Edit: fixed.

I spent a week porting a Java game to JRuby and I must admit.. I wouldn't actually mind a mixed syntax like this, but it did make do a double take ;-)

Heh. Yeah, I always find myself using the non-existent keyword now in Ruby and blowing things up by accident. It's the one place where Ruby is surprisingly unnatural.

Thanks for the catch. :)

    "There are only two hard problems in Computer Science:
    cache invalidation and naming things."
    
    -- Phil Karlton

Always helpful to see how someone else is solving the problem at scale.

Do you plan on open sourcing this?