<Swing Dev> 6179357: Generics: JList: Constructors & Model

[Florian Brunner]

In the case of JComboBox I think it's not even possible to define something like:

 class JComboBox<E>{
 ComboBoxModel<? extends E> getModel();
 setModel(ComboBoxModel<? extends E>);
 }

because JComboBox internally uses the ComboBoxModel.setSelectedItem method.

So the question is what do you think is better:

1) To look at each component individually and try to make each as flexible as possible. So in the 
JList/ JComboBox case this would mean:

 class JList<E>{
 ListModel<? extends E> getModel();
 setModel(ListModel<? extends E>);
 }

but 

 class JComboBox<E>{
 ComboBoxModel<E> getModel();
 setModel(ComboBoxModel<E>);
 }

2) Make the interfaces as consistent as possible over all components.
This would mean for the JList case to use somethink like:
 class JList<E>{
 ListModel<E> getModel();
 setModel(ListModel<E>);
 }

This approach is slightly less flexible than the approach 1), but cases where one could benefit from 
approach 1) are probably rare and there are various work-arounds (like: wrapping the model/ use a 
common base class for the generic parameter/ use raw type/... )

So what do you think? Approach 1) or 2)?

-Florian

Am Donnerstag, 19. Februar 2009 schrieb Florian Brunner:
> Well, there is probably no big issue with JList, because the ListModel is
> immutable.
>
> But when we add generics to JComboBox, which is similar to JList, the
> situation is a bit more controversial, because the ComboBoxModel is
> mutable.
>
> So if we have something like this:
> class JComboBox<E>{
> ComboBoxModel<? extends E> getModel();
> setModel(ComboBoxModel<? extends E>);
> }
>
> then something like this is not possible:
> JComboBox<Foo> cb = new JComboBox<Foo>(...);
> ...
> Foo foo;
> ComboBoxModel<? extends Foo> model = cb.getModel();
> model.setSelectedItem(foo); -> compile time error
>
> You would need to do an unchecked (-> not type-safe) cast first:
> ComboBoxModel<Foo> model = (ComboBoxModel<Foo>) cb.getModel();
>
> And type-safty is what generics is all about.
>
> -Florian
>
> Am Dienstag, 3. Februar 2009 schrieb Pavel Porvatov:
> > Hi Florian,
> >
> > > ----------------------------------------
> > >
> > > public JList(ListModel dataModel)
> > >
> > > {
> > >
> > > if (dataModel == null) {
> > >
> > > throw new IllegalArgumentException("dataModel must be non null");
> > >
> > > }
> > >
> > > // Register with the ToolTipManager so that tooltips from the
> > >
> > > // renderer show through.
> > >
> > > ToolTipManager toolTipManager = ToolTipManager.sharedInstance();
> > >
> > > toolTipManager.registerComponent(this);
> > >
> > > layoutOrientation = VERTICAL;
> > >
> > > this.dataModel = dataModel;
> > >
> > > selectionModel = createSelectionModel();
> > >
> > > setAutoscrolls(true);
> > >
> > > setOpaque(true);
> > >
> > > updateUI();
> > >
> > > }
> > >
> > > --->
> > >
> > > public JList(ListModel<E> dataModel)
> > >
> > > {
> > >
> > > if (dataModel == null) {
> > >
> > > throw new IllegalArgumentException("dataModel must be non null");
> > >
> > > }
> > >
> > > // Register with the ToolTipManager so that tooltips from the
> > >
> > > // renderer show through.
> > >
> > > ToolTipManager toolTipManager = ToolTipManager.sharedInstance();
> > >
> > > toolTipManager.registerComponent(this);
> > >
> > > layoutOrientation = VERTICAL;
> > >
> > > this.dataModel = dataModel;
> > >
> > > selectionModel = createSelectionModel();
> > >
> > > setAutoscrolls(true);
> > >
> > > setOpaque(true);
> > >
> > > updateUI();
> > >
> > > }
> > >
> > > We could define the signature also like this:
> > >
> > > public JList(ListModel<? extends E> dataModel)
> > >
> > > but then we would have to define the dataModel-field also with:
> > >
> > > private ListModel<? extends E> dataModel
> > >
> > > as well as the model-property. I don't think this would be a good idea
> > > and thus define the signature as:
> > >
> > > public JList(ListModel<E> dataModel)
> > >
> > > What do you think?
> >
> > Why do you think that "private ListModel<? extends E> dataModel" is not
> > a very good idea?
> >
> > Regards, Pavel