# Code Smell 181 - Nested Classes

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

> TL;DR: Don't use nested classes

# Problems

- [Bijection](https://maximilianocontieri.com/the-one-and-only-software-design-principle) fault to real world concepts.

- Lack of testability

- Lack of reuse

- Scopes and [namespaces complexity](https://stackoverflow.com/questions/47452783/code-style-and-smells-nested-classes)

# 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

[Gist Url]: # (https://gist.github.com/mcsee/836b485a9a9bb29e8292f9e79b867cbb)
```java
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

[Gist Url]: # (https://gist.github.com/mcsee/abcc622d9f0f27c40fd94202535dcced)
```java
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 the City concept
```

# 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](https://maximilianocontieri.com/what-is-wrong-with-software) set of concepts.

# More Info

- [W3 schools](https://www.w3schools.com/java/java_inner_classes.asp)

# Disclaimer

Code Smells are just my [opinion](https://maximilianocontieri.com/i-wrote-more-than-90-articles-on-2021-here-is-what-i-learned).

# Credits

Photo by [Dana Ward](https://unsplash.com/@danaward) on [Unsplash](https://unsplash.com/s/photos/spiral)  
 
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> Developers are drawn to complexity like moths to a flame, frequently with the same result.

_Neal Ford_
 
%[https://maximilianocontieri.com/software-engineering-great-quotes]

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This article is part of the CodeSmell Series.

%[https://maximilianocontieri.com/how-to-find-the-stinky-parts-of-your-code]