Re: Separation of API and implementation

I'm missing something or an Abstract Factory could help?
As long as you use the factory, you can ensure that your implementation of X
will use your implementation of Y.

--
Gabriel Claramunt
http://gabrielsw.blogspot.com

<hforco2@xxxxxxxxxxxxxx> wrote in message
news:1187099893.988357.302270@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I'm programming in Java, actually developing plugins in Eclipse, but I
think the general questions are relevant not only to Java.

I have an API defined in one plugin, in a set of packages. Call this
plugin A.

Another plugin contains my implementation, in a set of different
packages. Call this plugin B.

I have interfaces X and Y in A where X is defined as follows:

interface X {
void foo(Y y);
}

Now I implement X in B as follows:

class XImpl implements X {
public void foo (Y y) {
// Do something with Y
}
}

The problem I have is the 'Do something with Y'. Y is an interface and
has been designed to be reasonably generic i.e. not specific to the
implementation B.

But the implementation in B only works if I assume Y is actually B's
implementation of Y, say YImpl.

So 'Do something with Y' becomes:

// Cast to my implementation:
YImpl myImpl = (YImpl) y;

This raises several questions:

Am I ok to assume the cast will work?

This is presumably quite a common problem. In cases like this, is it
accepted that you won't get more than one implementation being mixed
with another, i.e. if I get passed back an interface from A then I can
assume it is my B implementation?

And how do I deal with unit-tests which create mock implementations?

Thoughts/comments much appreciated.



.

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