> From: Stephen McConnell [mailto:[EMAIL PROTECTED]
>
> What is interesting here is that ExcaliburComponentManager implements the
> Initializable and Composable interfaces without declaring the required
> exceptions and yet this compiles ok (which I confess I don't understand).
Stephen,
it is a basic thing about OO programming - a subclass should be able to
stand in for a superclass anywhere. That is, if SuperClass is a superclass
to SubClass, then:
void myMethod (SuperClass sc) { ... }
...
myMethod (new SubClass ());
should be valid, as the contract for SuperClass is inherited down to
SubClass. That is, SubClass must deliver at least as much as SuperClass.
Proceeding with the notion of contracts - each class requires something and
delivers something. This contract is inherited down the hierarchy, and a
subclass must not require more and must not deliver less than a superclass.
Thus, since Initializable can be seen as a superclass of
ExcaliburComponentManager, ECM must not require more and must not deliver
less than Initializable.
Initializable has a method initialize () throws Exception.
Requires: No parameters, ability for caller to handle Exception.
Delivers: Initializes the class.
Now, when ECM does *not* throw Exception:
Requires: No parameters.
Delivers: Initializes the class.
So ECM actually requires *less* than Initializable. This is perfectly
valid - the contract is upheld by the subclass. You class, however, does
throw an Exception and thus requires *more* than its superclass (ECM).
/LS
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