Difference between a HashMap and a dictionary ADT

Question

What is the difference between a Hash Map and dictionary ADT. And when to prefer one over another. For my programming assignment my instructor has asked to use one of them b

Answer 1

This Stack Overflow post does a good job explaining the key differences:

Java hashmap vs hashtable

Note that Hashtable is simply an implementation of the Dictionary ADT. Also note that Java considers Dictionary "obsolete".

The fact that Hashtable is synchronized doesn't buy you much for most uses. Use HashMap.