I am refactoring a large codebase where most of the classes are located in one package. For better modularity, I am creating subpackages for each functionality.
I remember learning somewhere that a package dependency graph should not have loops, but I don't know how to solve the following problem: Figure
is in package figure
, Layout
is in package layout
, Layout
requires the figure to perform layout, so package layout
depends on package figure
. But on the other hand, a Figure
can contain other Figure
s inside it, having its own Layout
, which makes package figure
dependent on package layout
.
I have though of some solutions, like creating a Container
interface which Figure
implements and putting it in the Layout
package. Is this a good solution? Any other possibilities?
Thanks
Best Answer
You should think about Inversion of Control
You basically define an interface for your
Layout
which is located somewhere near your Layout class in an own package so you would have an implementation package and a public interface package - for instance call itLayoutable
(I don't know if that's proper English). Now - Layout won't implement that interface but theFigure
class. Likewise you would create an interface for Figure that'sDrawable
for instance.So
Now - Figure implements Layoutable and thus can be used by Layout and (I'm not sure yet if that is what you wanted) - Layout implements Drawable and can be drawn in a Figure. The point is, that the class that exposes some service makes it available by an interface (here: Layout and Layoutable) - the class that wants to use that service has to implement the interface.
Then you would have something like a creator object that binds both together. So the creator would have a dependency to
Layout
as well as toFigure
, butLayout
andFigure
themselves would be independent.That's the rough idea.
An excellent source for solutions to this problems is the book Java Application Architecture by Kirk Knoernschild.