Java Map And Hashmap

It returns the set of the keys fetched from the map. You can say that in most cases it is better to use the map interface because generally you don't need to know about the details of the implementation and this way you can swap implementations in no time. Hashmap<k, v> hmap = new hashmap<k, v> ();

A map can be defined simply as a key value pair. It stores the data in (key, value) pairs, and you can access them by an index of another type (e.g. Java hashmap is a hash table based implementation of java's map interface.

All keys are unique in nature.

Let us consider below example where we have to count occurrences of each integer in given array of integers. A map cannot contain duplicate keys; Java hashmap allows null values and the null key. These keys are unique in nature and they identify values.