Code Smell 135 - Interfaces With just One Realization

Being generic and foreseeing the future is good.

UpdatedMay 30, 2022

•2 min read•View as Markdown

Code Smell 135 - Interfaces With just One Realization

Maxi Contieri

I’m a senior software engineer loving clean code, and declarative designs. S.O.L.I.D. and agile methodologies fan.

Comments (4)

Join the discussion

Cesar Kohl4y ago

Agreed!

Tapas Adhikary4y ago

Great article.

Maxi, let it go to 1K(articles from this series)

Maxi Contieri4y ago

Let's stress test Hashnode platform :)

Davide Bellone4y ago

What do you think of interfaces implemented by only one class, when that class represents a Service and not a DTO?

Something like

public interface IDoSomething{
void Do();
}

public class DoSomething : IDoSomething{
void Do();
}

Maxi Contieri4y ago

IDoSomething is a name problem. I've never seen an IDoSomething in real world. I assume it is a bad convention.

If this a service provided as an API interface for other systems it might suit the Exceptions scenario.

If it is for internal use is a code smell on premature generalization

Miki Szeles4y ago

Great article again, Maxi. I love your series. 😊

Code Smells

Part 1 of 50

In this series, we will see several symptoms and situations that make us doubt the quality of our developments. We will present possible solutions. Most are just clues. They are no hard rules.

Problems

Speculative Design
Complexity
Over-Engineering

Solutions

Remove the interface until you get more examples

Context

In the past, programmers told us to design for change.

Nowadays, We follow the scientific method.

Whenever we find a duplication we remove it.

Not before.

Sample Code

Wrong

public interface Vehicle {
    public void start();
    public void stop();
}

public class Car implements Vehicle {
    public void start() {
        System.out.println("Running...");
    }
    public void stop() {
        System.out.println("Stopping...");
    }
}

// No more vehicles??

Right

public class Car {
    public void start() {
        System.out.println("Running...");
    }
    public void stop() {
        System.out.println("Stopping...");
    }
}

// Wait until more vehicles are discovered

Detection

[X] Automatic

This is very easy for our linters since they can trace this error at compile time.

Exceptions

This rule applies to inter system definition and business logic.

Some frameworks define an Interface as protocol to be fulfilled.

On our bijections we need to model existing real world protocols.

Interfaces are the MAPPER correspondence to protocol.

Dependency injection protocols declare interfaces that are fulfilled with their realizations. Until then, they can be empty.

Relations

https://maximilianocontieri.com/code-smell-130-addressimpl

https://maximilianocontieri.com/code-smell-136-classes-with-just-one-subclass

Conclusion

We need to wait for abstractions and not be creative and speculative

Credits

Photo by Brian Kostiuk on Unsplash

I love software, because if you can imagine something, you can build it.

Ray Ozzie

https://maximilianocontieri.com/software-engineering-great-quotes

This article is part of the CodeSmell Series.

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

Code Smell 135 - Interfaces With just One Realization

Comments (4)

Code Smells

More from this blog

AI Coding Tip 031 - Stop Over-Prompting Reasoning Models

AI Coding Tip 030 - Script Your Skills, Not Your Prompts

AI Coding Tip 029 - Stop Using One Model for Everything

AI Coding Tip 028 - Build a Company Brain

AI Coding Tip 027 - Force Code Standards

Problems

Solutions

Context

Sample Code

Wrong

Right

Detection

Exceptions

Tags

Relations

Conclusion

Credits

Command Palette

Comments (4)

Code Smells

More from this blog

Problems

Solutions

Context

Sample Code

Wrong

Right

Detection

Exceptions

Tags

Relations

Conclusion

Credits