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.
Let me put in simple words.
this operator returns the object of current class. Here in this case Farmer.this will return an object of the class Farmer and you are trying to access class member variable age with the help of that object.
There are only 10 types of people in the world: those who understand ternary, those who don't, and those who mistake it for binary.