hashmap class is not syncronized but hasTable is syncronized
. both stores key and value. hashtable is part of legasy
class we can use enumerator interface of this hashtable class.

Hashtable will not allow null key nor values,where as 
Hashmap allows null key and values

---HashTable is synchronised BUT hashmap is not synchronised
---HashTable not allow null keys and null values BUT 
HashMap allow only one null key and multiple null values
---HashTable not allow Duplicate keys and Douplicate values 
are allowed.

Hashmap is not Synchronized where as Hashtable  is 
Synchronized.

Hashmap allows null values as keys.
Hashtable doesn't allows null values as keys.