What is the need of hashmaps

Answer 1

Hash map is like collection of pairs key-parameter.
Basing on key name you can get the value which is connected to that key.
Possibilities of using it are almost limitless.
For example it may be used to dynamically store data.

Answer 2

i believe it allows for extremely fast lookups where the chance for looking up the same index more than once is possible. In the case of a duplicate index, the algorithm-generated lookup has to deal with what is called a "collision", at which point additional steps are then taken for resolving the search.