What Index Is and How To Use It in Java
An Index is a structure that facilitates search in your data. Is a pretty general term and doesn't belong to some language or database. In order to explain it let's create a way to search users for specific criteria like name, id, birth date, etc.
Quickly Searching Among Millions of User Entries
Let's assume that we have 1 million users. As a requirement, we have to expose API to search users by specific criteria. Obviously, simple iteration will take too much time. So let's sort this problem using indexes (or simply saying by pre-generating some data that accelerate lookup during API calls). So first place let's define our User class and Search interface: