Searching and indexing

When creating a clean storage that is based on key-values, we may find that we have lost some of the extra searching capabilities that traditional databases offer. Mainly, we now can't find records within a dataset without knowing the primary key to the entry. However, fear not. Hazelcast provides similar capabilities that allow you to search its maps using predefined indexes. These can be either ordered (ascending) or unordered, depending on our particular data needs. However, keep in mind that indexing doesn't come for free. The internal lookup table that is used to quickly search the reads is maintained as we make changes to the map. This will add latency to every write operation in the namespace.

So firstly, let's create a new plain old Java object (POJO) to represent a city, as follows:

import java.io.Serializable;

public class City implements Serializable, Comparable<City> {
  private String name;
  private String country;
  private int population...