Question

Say I have a HashMap of HashMaps defined like this:

hashMap = new HashMap<String, HashMap<String, Integer>>();

How would I abstract over this to make the definition more clear?

Answer 1

If I interpret your question correctly, you have a collection which maps objects together and want to know if there is a way to do it that reads better.

It’s best if we define a purpose for each of the elements, so as an example:

Map<String,        // ZIP code   (e.g. 6009)
    Map<String,    // Name       (e.g. John Smith)
        Integer>>  // Age        (e.g. 42)

In this case, you can create the following class:

class Person {
  private String name;
  private Integer age;

  // Constructor and getters etc.
}

This simplifies your collection to:

Map<String,         // ZIP/Postal code
    List<Person>>   // List of people in this postal code.

You can then simplify it further if you want, but this gives you an idea of what steps to take. The most important thing is to use names that make sense.