I have a number of sets of matched parameterized classes: a bean, a
presenter, and a view.
The presenters and views have parallel inheritance hierarchies (where
T is the bean type, P the presenter type, and V is the view type):
public class CompA extends CompItem<AInfo, CompA, CompAView>
public class CompB extends CompItem<BInfo, CompB, CompBView>
public class CompAView extends CompItemView<AInfo, CompA, CompAView>
public class CompBView extends CompItemView<BInfo, CompB, CompBView>
public class CompItemView<T extends CompItemInfo,
P extends AbstractCompItem<T, P, V>,
V extends CompItemViewInterface<T, P,
V>>
extends AbstractCompItemView<T, P, V>
implements CompItemViewInterface<T, P, V>
public abstract class CompItem<T extends CompItemInfo,
P extends AbstractCompItem<T, P, V>,
V extends CompItemViewInterface<T,
P, V>>
extends AbstractCompItem<T, P, V>
implements CompWidget<T>
Many of the views are the same, so I wanted to just use the base view
class instead of creating a separate view class for each presenter.
So I tried:
public class CompA extends CompItem<AInfo, CompA, CompItemView>
But I get an error that says "The type CompItemView is not a valid
substitute for the bounded parameter<V extends
CompItemViewInterface<T,P,V>> of the type CompItem<T,P,V>.
Why can I use a class that extends CompItemView for the V type, and
not CompItemView itself?
'P'. This type of generics circularity has a place, but it's often the result
of confusion also. Which is it for you? Why does 'P' extend its own type?
The combination is likely what's killing you. Remember that 'Foo extends Bar'
there at all - and do your covariance correctly your problem should vanish. I
Honi soit qui mal y pense.