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List:       openjdk-swing-dev
Subject:    <Swing Dev> 6179357: Generics: JList: ListCellRenderer & prototypeCellValue
From:       fbrunnerlist () gmx ! ch (Florian Brunner)
Date:       2009-02-26 21:28:18
Message-ID: 200902262228.19105.fbrunnerlist () gmx ! ch
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So, 2 votes for option 3), which is a reasonable one, I think.

Pavel? Anyone else?

-Florian

Am Sonntag, 22. Februar 2009 schrieb Erik Lundqvist:
> Hi,
> ListCellRenderer should absolutely be generic which rules out option 1 :)
> I cannot remember ever using the prototypeCellValue so a bit worried about
> saying too much about how people are using it, but it does not seem
> unreasonable that it should be of the same type so I would go for Option 3
> as well which seems the simpler and most common use case.
>
> //erik
>
> 2009/2/21 Florian Brunner <fbrunnerlist at gmx.ch>
>
> > Hi,
> >
> > I think adding generics to the ListCellRenderer could also be useful. The
> > problem is that in JList
> > the same cell renderer is used for the items as for the
> > prototypeCellValue - and the
> > prototypeCellValue doesn't necessarily have be of the same type as the
> > items!
> >
> > So I think we have 3 options:
> >
> > 1) Don't provide a generic cell renderer/ allow only Object as parameter
> > for the cell renderer in
> > JList.
> >
> > 2) Add a second generic parameter. Eg. something like:
> > class JList <E, P super E>{ ... }
> >
> > and use P for the prototypeCellValue property as well as for the cell
> > renderer.
> >
> > 3) Require prototypeCellValue to be of type E. In the probably rare
> > cases, where this is a problem
> > one can still specify a common base class of the items and the
> > prototypeCellValue as the generic
> > parameter or use a raw type JList.
> >
> >
> >
> > I think it would be a pity not to provide a generic cell renderer (1) and
> > think 2) is inconvenient
> > and confusing, since in my experiences prototypeCellValue is only used
> > rarely.
> >
> > So I'm voting for 3). For which option do you vote? For which reason?
> >
> >
> >
> > Note I also propose to use:
> >
> > ListCellRenderer<? super E> cellRenderer
> >
> > rather than
> >
> > ListCellRenderer<E> cellRenderer
> >
> > in JList. This would make it more flexible. Do you agree? (It's actually
> > the first time, I think, I
> > use 'super' with generics myself, but I think this is a good use case of
> > it. So any comments are
> > welcome. ;-) )
> >
> > -Florian




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