Xcode Installation: how to prevent automatic upgrade of Xcode

I have been using Xcode 6.4. I have downloaded 7.0 beta 6 from the developer.apple.com service, and had both versions happily cohabited for weeks. Somehow, Xcode 6.4 was replaced automagically by 7.0, probably from the App Store.

I want to prevent automatic Xcode update from happening in the future, and manually update Xcode when I want or need to. It appears that:

You will be notified when the updates are ready to be installed

and

Install app updates

are mutually exclusive, and opting for app updates voids the notification.

Where to check the Download newly available app updates but do not Download OS X updates box, if such a feature exists? Is it possible to get notified prior every installation?

Under your Mac's System Preferences there should be a item called App Store where you can turn off automatic updates from App Store (which turns off all app updates, not only Xcode).

The You will be notified when the updates are ready to be installed only applies to the downloading of the data and if you check this box it will therefore download without your explicit approval. It will not install unless you check the Install app updates.