What is hashtable?

A hash table is a generic data structure providing for fast and random retrieval of objects. It is sometimes called a map or a dictionary (although the implementations may differ). Its a key-value pairs. The tenet of a hash table is that the location of an object in the data structure is computed from the key associated with the object when it is stored into the hash table. For that reason, retrieving an object from a hash table is very fast. Of course, the key associated with the object must be unique.