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Editorial Team
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Asked: 2026-05-15T07:16:34+00:00

I suppose this could go for many OO languages. I’m building my domain objects

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I suppose this could go for many OO languages. I’m building my domain objects and am not sure where the best place is for the interfaces & abstract classes.

If I have a pets package with various implementations of the APet abstract class: should it live side-by-side with them or in the parent package?

How about interfaces? It seems like they almost have to live above the implementations in the parent package, since there could potentially be other subpackages which implement it, while there seems to be a stronger correlation between one abstract class and a subpackage.

e.g.

com.foo
com.foo.IConsumer (interface)
com.foo.APet (abstract)
com.foo.pets.Dog extends APet implements IConsumer

OR

com.foo
com.foo.IConsumer (interface)
com.foo.pets.APet (abstract)
com.foo.pets.Dog extends APet implements IConsumer

or something else?

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1 Answer

  1. Editorial Team

    IMO interfaces and abstract classes are not so different in this respect. It is often better to keep the implementations in a separate package, especially if they are instantiated via a factory. This way these can be kept package private, so their implementation details are better hidden from clients.

    So I would go with something like the first choice.

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