Code Smell 126 - Fake Null Object

Null Objects are great alternatives to The Billion Dollar Mistake. Sometimes we don't need them

TL;DR: Don't abuse patterns. Even NullObject.

Problems

• Empty Classes

• Namespace Polluting

• Duplicated Behavior

Solutions

1. Create Null Objects instantiating real-object classes.

Context

Null Object pattern is a great alternative to Nulls and IFs (Both are code smells).

The structure of the pattern tells us to create a hierarchy.

This is not really necessary, we need real objects to be polymorphic to null objects.

Inheritance is not a proper way to achieve polymorphism.

A simple solution is to create a real object behaving like a null one.

For example: '0' is numbers' null object.

'' (or "") is String's null object

An empty collection is collection's null object.

Sample Code

Wrong

abstract class Address {
    public abstract String getCity();
    public abstract String getState();
    public abstract String getZipCode();
}

//Using inheritance for null objects is a mistake
//We should use interfaces (when available)
public class NullAddress extends Address {

    public NullAddress() { }

    public String getCity() {
        return Constants.EMPTY_STRING;
    }

    public String getState() {
        return Constants.EMPTY_STRING;
    }

    public String getZipCode() {
        return Constants.EMPTY_STRING;
    }

}

public class RealAddress extends Address {

    private String zipCode;
    private String city;
    private String state;

    public RealAddress(String city, String state, String zipCode) {
        this.city = city;
        this.state = state;
        this.zipCode = zipCode;
    }

    public String getZipCode() {
        return zipCode;
    }

    public String getCity() {
        return city;
    }

    public String getState() {
        return state;
    }

}

Right

//There are just "addresses"
public class Address {

    private String zipCode;
    private String city;
    private String state;

    public Address(String city, String state, String zipCode) {
    //Looks anemic :(
        this.city = city;
        this.state = state;
        this.zipCode = zipCode;
    }

    public String zipCode() {
        return zipCode;
    }

    public String city() {
        return city;
    }

    public String state() {
        return state;
    }

}

Address nullAddress = new Address(Constants.EMPTY_STRING, Constants.EMPTY_STRING, Constants.EMPTY_STRING);
//we have our null object
//we should NOT assign it to a singleton, static or global
//It behaves like a null object. That's enough
//No premature optimizations

Detection

[X] Manual

This is a semantic smell.

Tags

• Null

Conclusion

Creating Null Object classes is sometimes overdesign.

We need to create a real object.

This real object should never be global, singleton, or static.

Too many smells to avoid.

Relations

Code Smell 12 - Null

Maxi Contieri ・ Oct 31 '20

#codenewbie #tutorial #oop

Code Smell 32 - Singletons

Maxi Contieri ・ Nov 23 '20

#codenewbie #tutorial #webdev #programming

Code Smell 114 - Empty Class

Maxi Contieri ・ Feb 12 '22

#oop #tutorial #cleancode #webdev

Code Smell 18 — Static Functions

Maxi Contieri ・ Nov 6 '20

#codenewbie #tutorial #development #coding

Code Smell 17 - Global Functions

Maxi Contieri ・ Nov 5 '20

#codenewbie #development #tutorial

More Info

• Null: The Billion Dollar Mistake

• Null Object Wikipedia

• Refactoring.guru

Credits

Photo by Juan Davila on Unsplash

Thanks to Hernan Wilkinson for this idea on his course Diseño a la Gorra (in Spanish)

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This article is part of the CodeSmell Series.

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