Answer Posted / khalid

Both provide key-value access to data. The Hashtable is one
of the original collection classes in Java. HashMap is part
of the new Collections Framework, added with Java 2, v1.2.
The key difference between the two is that access to the
Hashtable is synchronized on the table while access to the
HashMap isn't. You can add it, but it isn't there by
default.

Another difference is that iterator in the HashMap is fail-
safe while the enumerator for the Hashtable isn't. If you
change the map while iterating, you'll know.

And, a third difference is that HashMap permits null values
in it, while Hashtable doesn't.

For new code, I would tend to always use HashMap.

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