Hi mobilegeek

The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls. (HashMap allows null values as key and value whereas Hashtable doesn’t allow). HashMap does not guarantee that the order of the map will remain constant over time. HashMap is unsynchronized
and Hashtable is synchronized.

Oxygen

* Map provides Collection views instead of direct support for iteration via Enumeration objects. Collection views greatly enhance the expressiveness of the interface.
* Map allows you to iterate over keys, values, or key-value pairs; Hashtable does not provide the third option.
* Map provides a safe way to remove entries in the midst of iteration; Hashtable did not.