Can a Locked Door Stop an Elf?

[kiricat2001]

No: HPFGUIDX 85966

In reading the Chapter Six summary, it is mentioned that Ron locks 
the door of the bedroom he shares with Harry because he doesn't want 
Kreacher to be able to wander in in the middle of the night.  

Why would a locked door stop Kreacher, if he really wanted to get in?

We've seen Dobby apparate (or whatever that mode of transport is 
called for elves) into and out of Privet Drive, into and out of the 
Hospital in CoS.  So it seems that elves have that ability.  Fred and 
George apparate into the bedroom in Chapter six, so the house does 
not have anti-apparition wards on the inside.  

Yet, Ron thinks locking the door will keep Kreacher out.  Is Ron 
merely exhibiting ignorance of elf powers? Is Kreacher only able to 
enter rooms by walking into them?  Maybe so - IIRC we always see him 
come into a room by shuffling in through the doorway. Is this a tiny 
flint?  Would I be better off spending my time basting the turkey???

Marianne