Answer Posted / knowledge_finder

1. HashMap allows null values for key and value whereas
Hashtable doesnt allow.
2. HashMap does not guarantee that the order of the map will
remain constant over time. 3. HashMap is non synchronized
where as Hashtable is synchronized.
4. HashTable is an Old java class but Hashmap is a new java
class in java 2.
5. In HashTable you can change the iteration but in the case
of HashMap you can change the iteration but you will get a
java.util.ConcurrentModificationException.

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