For fun I'm messing around with Cocoa programming using the book Learning Cocoa (actually the 2001 first edition that I bought cheap from Half Price Books) and writing the examples in Java. At the moment I've got to the chapter on Cocoa's Multiple-Document Architecture and I spend a frustrating couple of hours trying to get the simple RTF example to work.

Whenever I started the application I would get a popup saying "No document could be created." and the Run Log window would show "The DocumentType type doesn't map to any NSDocumentClass.". I'd moved the NSDocument subclass into a package so I expected that when I set up the Document Class entry in the Document Types configuration I would enter com.zanthan.apple.MyDocument. Not so, the correct way to do this is to enter com/zanthan/apple/MyDocument. This information I found from this cocoadev post.