What's to clarify? Yes, LinkedHashMap extends HashMap. This is stated clearly in the API. It's not stated in the book - but that doesn't mean it's not true. There are many facts that aren't stated in K&B. This is true of most book - they don't attempt to tell you every single thing about the subject; they tell you the important things. The fact that LinkedHashMap implements Map is important; the fact that it extends HashMap isn't, really. though it's fairly obvious from the name.