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cyclic dependency  RSS feed

 
scott beveridge
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Hi,

I'm trying to get a few classes to call each other's methods. It's been driving me nuts for a while and eventually I read that this was a cyclic dependency, which I understand is bad and symptomatic of poor design, probably true in this case.

My qustion is what code do I need to add to allow B's methods to call A's and vice versa?

Thanks.

Scott
 
Svend Rost
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Please correct me, if this is a bad approach

How about the following ?

public class A:
instance var:
-B
instance methods:
+setB(B newB)
+doStuffOnB()

public class B:
instance var:
-A
instance methods:
+setA(A newA)
+doStuffOnA()

/Svend Rost
 
scott beveridge
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Oh sorry, the dependency exists between more than two classes.
What I want to do is farely simple: take an input and pass it to an object, perform an operation on it and pass it on. Eventually it is passed back along the chain in the reverse order. Surely there is an easy way to do this?
 
Stan James
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Cyclic dependencies are fairly common in simple callbacks. One way to avoid them is to code to interfaces so everyone depends on interfaces and the classes are nicely decoupled.

Now all three classes depend on IService and IClient, RunTest depends on the two implementations, but the two implementations do not depend on each other. That's a fair bit of effort to remove the cycle, but it allows flexible packaging of interfaces and implementations to achieve reusable components or pluggable components. Good clean fun?
 
scott beveridge
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Thanks for the replys gentlemen, they were a great help. I now have something which does what it is supposed to, so its on to stage 2.

The first time I heard of a callback was when Stan mentioned it in his post. After much research and experimentation I can move on. All those books about java apparently teach you only how to write code, not programs.

So thanks again, and expect more questions.

BTW, Stan I looked into your sig line- very cool stuff.

Scott
 
Stan James
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"Conway's Law" seeme pretty dull, but it shook me up the first time I read it and recently it seemed like a pretty profound analysis of a situation at work so I dragged it out here.

Keep having fun with design. The OO, UML, etc forum down the page has lots of discussion on OO principles.
 
It is sorta covered in the JavaRanch Style Guide.
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