This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
why not try it with a noddy program to see? You could put String representations of integer numbers into a hashtable indexed by the same integer number as an Integer object. Should be easy enough to knock up with a for loop (but make sure you have a LOT of memory first). Wouldn't a persistent data store be a better option in the long run?