Why LinkedHashMap is ordered?

Question

Why is LinkedHashMap is ordered? If it implements the Map interface and extends AbstractMap and HashMap, Which of them provides the ordering feature?

Answer 1

From the documentation of LinkedHashMap

Hash table and linked list implementation of the Map interface, with predictable iteration order. This implementation differs from HashMap in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is normally the order in which keys were inserted into the map (insertion-order).

So the ordering comes from the implementation of LinkedHashMap and not from extending java.util.AbstractMap<K,V> or java.util.HashMap<K,V>

Answer 2

LinkedHashMap is ordered because that is part of its contract. See http://docs.oracle.com/javase/7/docs/api/java/util/LinkedHashMap.html, for example "Hash table and linked list implementation of the Map interface, with predictable iteration order.".

It also states how it is different from HashMap: "This implementation differs from HashMap in that it maintains a doubly-linked list running through all of its entries."