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Cover image for Code Smell 181 - Nested Classes
Maxi Contieri ⭐⭐⭐
Maxi Contieri ⭐⭐⭐

Posted on • Originally published at maximilianocontieri.com

Code Smell 181 - Nested Classes

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

TL;DR: Don't use nested classes

Problems

Solutions

  1. Make the class public

  2. Keep the public class under your own namespace/module.

  3. 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"
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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
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Detection

[X] Automatic

Since this is a language feature, we can detect it and avoid its usage.

Tags

  • Hierarchies

Conclusion

Many features are bloated with complex features.

We seldom need these new pop culture features.

We need to keep a minimal set of concepts.

More Info

Disclaimer

Code Smells are just my opinion.

Credits

Photo by Dana Ward on Unsplash


Developers are drawn to complexity like moths to a flame, frequently with the same result.

Neal Ford


This article is part of the CodeSmell Series.

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