Assume Map interface has 10 public methods. Hashmap class implemented Map interface and some extra methods, total 20 public methods. Map map = new Hashmap() From this map object how many methods can I access. Can I access 10 or 20?
You can only access the 10 methods of Map through the reference map. You would, in your example, have to cast the reference map to a HashMap reference if you wanted to access all of HashMap's methods. For instance: ((HashMap)map).someMethodSpecificToHashMap()