Posted on Nov 22, 2022 • Originally published at maximilianocontieri.com

Code Smell 181 - Nested Classes

#webdev #beginners #programming #php

Nested or Pseudo-Private Classes seem great for hiding implementation details.

TL;DR: Don't use nested classes

Problems

Bijection fault to real world concepts.
Lack of testability
Lack of reuse
Scopes and namespaces complexity

Solutions

Make the class public
Keep the public class under your own namespace/module.
Use a Facade to the external world to hide it.

Context

Some languages allow us to create private concepts that only live inside a more significant idea.

These classes are harder to test, harder to debug, and reuse.

Sample Code

Wrong

class Address { String description = "Address: "; public class City { String name = "Doha"; } } public class Main { public static void main(String[] args) { Address homeAddress = new Address(); Address.City homeCity = homeAddress.new City(); System.out.println(homeAddress.description + homeCity.name); } } // The output is "Adress: Doha" // // If we change privacy to 'private class City'  // // We get an error " Address.City has private access in Address"

Right

class Address { String description = "Address: "; } class City { String name = "Doha"; } public class Main { public static void main(String[] args) { Address homeAddress = new Address(); City homeCity = new City(); System.out.println(homeAddress.description + homeCity.name); } } // The output is "Adress: Doha" // // Now we can reuse and test City concept