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Cover image for Code Smell 61 - Coupling to Classes

Code Smell 61 - Coupling to Classes

mcsee profile image Maxi Contieri ・2 min read

Classes are handy. We can call them and invoke them any time. Is this good?

Problems

  • Coupling

  • Extensibility

  • Hard to mock

Solutions

  1. Use interfaces or traits (if available).

  2. Use Dependency Injection.

  3. Favor Loose Coupling.

Sample Code

Wrong

Right

Detection

We can use almost any linter to find references to classes. We should not abuse since many uses might be false positives.

Tags

  • Coupling

Conclusion

Dependencies to Interfaces make a system less coupled and thus more extensible and testable.

Interfaces change less often than concrete implementations.

Some objects implement many interfaces, declaring which part depends on which interface makes the coupling more granular and the object more cohesive.

Relations

More info

Coupling

Wikipedia

Credits

Photo by Marco Bianchetti on Unsplash


When your code depends on an interface, that dependency is usually very minor and unobtrusive. Your code doesn’t have to change unless the interface changes, and interfaces typically change far less often than the code behind them. When you have an interface, you can edit classes that implement that interface or add new classes that implement the interface, all without impacting code that uses the interface.

For this reason, it is better to depend on interfaces or abstract classes than it is to depend on concrete classes. When you depend on less volatile things, you minimize the chance that particular changes will trigger massive recompilation.

Michael Feathers


Discussion (5)

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chrisza4 profile image
Chakrit Likitkhajorn

I am confused. The solution said that favor loose coupling and the conclusion favor dependency on to the interface. But in the wrong example, MyDomain class depends on interface and in the right example it depends on class.

Maybe it is swapped?

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mcsee profile image
Maxi Contieri Author

thank you very much for pointing it out

last minute change. :)
Of course coupled.java was the wrong one!

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michaelcurrin profile image
Michael • Edited

Hi. I don't know this is an issue with your embedding or just a limitation of the platforms, but when I look at 3 different posts of yours for the first time, then initially the same file is used. On reloading immediately then it is fixed.

Perhaps its because of how multiple files exist in one gist. But doesn't explain buggy gist behavior.

First
Second

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mcsee profile image
Maxi Contieri Author

Hi.

There is a bug with dev.to app version that messes up gists.
This is not happening on the website

Can you check this out?

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michaelcurrin profile image
Michael

It does sound like a bug. I don't think I've seen gists much before here.

I am using mobile web.

Strangely after the first 3 post problems, on the 4th post I clicked, it worked right first time around.

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