From: Leo Sutic wrote: > > 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).
Leo: Your quite right - the distinction here is that ECM does not need to throw an exception relative to its own implementation characteristics. However, this limits the potential for supertypes because a supertype cannot introduce anything that would potential raise an exception during initalize. Conclusion - there isn't a fault in ECM in terms of its own internal implementation - but elimination of the throws Exception delcaration effectively eliminates the possibility for supertypes that need this (which was my case). Steve. -- To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]> For additional commands, e-mail: <mailto:[EMAIL PROTECTED]>
