Difference between HashMap and Hashtable in Java

HashMap:

1. HashMap object is not synchronized by default.
2. In case of a single thread , using HashMap is faster than the Hashtable.
3. HashMap allows null keys and null values to be stored.
4. Iterator in the HashMap is fail-fast . This means iterator will produce exception if concurrent
updates are made to the HashMap.
5. We can make HashMap object synchronied using synchronizedMap() method as:

Collections.synchronizedMap(new HashMap())

Hashtable:

1. Hashtable object is synchronized by default.
2.In case fo multiple threads , using Hashtable is advisable. With a single thread, Hashtable
becomes slow.
3.Hashtable does not allow null keys or values.
4.Enumeration for the Hashtable is not fail-fast. This means even if concurrent updations
are done to to Hashtable, there will not be any incorrect results produced by the Enumeration.