I'm following along with a tutorial and came across some code like this (item is of class Item):

ModelLoader.setCustomModelResourceLocation(item, meta, new ModelResourceLocation(item.getRegistryName(), id));

 

Wondering where getRegistryName() came from, I found it in IForgeRegistryEntry (in the class Impl). However, I don't know (even after reading up on generics) what this means:

 

 public static class Impl<T  extends IForgeRegistryEntry<T>> implements IForgeRegistryEntry<T>

 

I did see that Item itself extends IForgeRegistryEntry.Impl<T>. Does the above class state that anything calling its methods must extend IForgeRegistryEntry? 

Yeah, but it looks like IForgeRegistry is specifically looking for something that extends IForgeRegistry. Why am I allowed to call its methods using Item?