I'm looking at creating a mod that adds a few extra world types to the game. I've already found the WorldType class and I've been able to add extensions to it without problems. However this has all been with Minecraft running in debug mod from Eclipse. I surmise that if I were to try and run the mod from a normal instance of Minecraft with Forge installed this would not work and when I tested this was indeed the case. I get class not found exceptions galore because I'm extending a Minecraft class. I've not found any hooks in Forge for adding new world types. Am I incorrect in saying that or did I miss something big?

Hey there! Lucky for you I just added my own WorldType and I'll gladly share how I did it. It's actually a pretty long process, well not a long process more like annoying to code involving multiple files. But I used this tutorial on the minecraftforums and tweaked it just a slight bit to my liking. I'm sure you can figure it out by reading this tutorial. http://www.minecraftforum.net/topic/1261568-creating-modsmodloaderhow-to-create-a-simple-worldtypejune-1-2012/page__hl__%20worldtype

Thank you very much for the help! Extra help is very much appreciated. Some of this code from Minecraft is a bit strange. I figured out just recently that some of what I was doing I was just doing wrong. I have been able to correct some of it. I've noticed that there are a lot of strange restrictions and choices that were made in the design of the world generation system. One of the problems I encountered when making a Void world type (just to get the hang of it) was that it is very difficult to place the starter block at spawn since you don't know where spawn is yet. I can understand the reasoning since there are lots of rules for where spawn is but it makes things difficult. Which is why I'm glad you shared the link. The example of a Void world should help.