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From: sclaflin <steve@steveclaflin.com>
Newsgroups: comp.lang.java.programmer
Subject: Hairy generics question
Date: Tue, 21 Feb 2012 06:30:51 -0800 (PST)
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.java.programmer:12232

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?