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Is it a bad practice to "mix class and interfaces in one package"?

I just found something that I had never heard of before, and I disagree (by now). In the answer I read "why mix class and interfaces in one package"

So it’s interesting if there are reasons to separate interfaces and implementations in Java.

I know that we are not required to have all implementations in an interface package, but is it (sometimes) reasonable not to have it?

Yours faithfully
Mike
[; -)

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4 answers

Reasons to store interfaces and implementations in separate packages:

clear code base . It looks “better”, more accurate if we have one package with interfaces and another with implementations (usually something.impl namespace). And the code structure shows / reflects what you code against interfaces.

access modifiers . We can use package private access modifiers for the package private API to implement related interfaces.

The structure of the library . Perhaps one day you may decide to create different libraries for the API (s) and implementation (s). Then it’s nice to have interfaces and implementations in different packages. Thus, you can change the assembly without refactoring your code base.

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I agree with org.life.java - I will have the service and basic packages service.impl, but always in this form.

I do not agree with the phrase "bad practice." This is too strong.

The java.util Collections API API contradicts this advice. I would not want to be the one who told Joshua Bloch that he did a "bad job."

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For OSGi, it is almost necessary to use separate AFAIK packages so that you can export / import the API without exporting / importing the implementation.

For interfaces that are only internally, however, it is not a problem to save everything in one package.

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This is not bad, but, of course, it’s good practice to distinguish between interface and implementation in different packages.

eg

 com.mycompany.domain.service com.mycompany.domain.service.impl

<strong> Benefits:

  • Unified packaging structure
  • For a while, when you want to process only certain classes, you can split it into a package
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