This probably isn't 1.9 specific but I'm coding for 1.9. Let's say I have this code:

 

NBTTagCompound tag1 = new NBTTagCompound();
tag1.setString("alpha-string", "Alex");
tag1.setString("bravo-string", "John");

FMLLog.info(tag1.toString());

NBTTagCompound tag2 = new NBTTagCompound();
tag2.setString("charlie-string", "Chris");
tag2.setString("delta-string", "Bob");

NBTTagList tag3 = new NBTTagList();
tag3.appendTag(new NBTTagInt(3));
tag3.appendTag(new NBTTagInt(2));
tag3.appendTag(new NBTTagInt(1));

tag2.setTag("echo-tag-list", tag3);

FMLLog.info(tag2.toString());

 

Which prints this:

 

{alpha-string:"Alex",bravo-string:"John"}
{charlie-string:"Chris",echo-tag-list:[0:3,1:2,2:1],delta-string:"Bob"}

 

For the first compound tag the result makes sense, alpha-string was added before bravo-string and thus appears first. But for the second compound tag the result doesn't follow suit. echo-tag-list appears before delta-string despite being added after. Why is this?

I'm pretty sure that internally it get treated like a hashmap of <String, NBTBase> and hashmaps do not guarantee an order.

Ahh okay thanks guys.