<Swing Dev> [PATCH] 6179357: Generics: JList

[Florian Brunner]

Hi Pavel,

I don't understand, what exactly you want to do. DefaultListCellRender 
implements ListCellRenderer<Object>, which means it is an 
implementation, which can be savely (without risking a 
ClassCastException) be used with ANY object. That is due the fact, that 
it checks if it is an instance of Icon or else calls Object.toString, 
which is defined for any Object:

if (value instanceof Icon) {
        setIcon((Icon)value);
        setText("");
    }
    else {
        setIcon(null);
        setText((value == null) ? "" : value.toString());
    }

There is no gain in calling eg.:
new DefaultListCellRender<Foo>()

because the existing implementation (DefaultListCellRender implements 
ListCellRenderer<Object>) already handles Foo.

The only limitation is with sub-classing: Subclasses cannot change the 
parameter type.
But this can be solved with using composition instead of inheritance, eg:

public class FooRenderer implements ListCellRenderer<Foo>{
    private DefaultListCellRender defaultRenderer = new 
DefaultListCellRender();
 
 public Component getListCellRendererComponent(
        JList<? extends Foo> list,
        Foo value,
        int index,
        boolean isSelected,
        boolean cellHasFocus)
    {
        doSomethingWithFoo(foo);
        return defaultRenderer.getListCellRendererComponent(list, value, 
index, isSelected, cellHasFocus);
    }

  private void doSomethingWithFoo(Foo foo){
      // do something
  }
}

So, I think the answer is yes, it could be changed, but I see no real 
benefit and more, client code needs then to specify a parameter, which 
currently it doesn't.

-Florian

Pavel Porvatov schrieb:
> Hi Florian,
>
> I have a question about the DefaultListCellRenderer class. Can we 
> modify it to use generics?
>
> Thanks, Pavel
>
>> Hi Pavel, hi Alexander,
>>
>> I'm back from holiday.
>>
>> What is the status of this patch? Any news?
>>
>> -Florian
>>
>> Alexander Potochkin schrieb:
>>> Hello Florian
>>>
>>>> Great! :-)
>>>>
>>>> In the case of other issues please note that I'm on holiday until 
>>>> the end of next week.
>>>
>>> Have a nice holiday!
>>>
>>> (I am reviewing the fix right now)
>>>
>>> Thanks
>>> alexp
>>>
>>>>
>>>> -Florian
>>>>
>>>> Pavel Porvatov schrieb:
>>>>> Hi Florian,
>>>>>
>>>>>> Hi Pavel,
>>>>>>
>>>>>> I agree that we should avoid to mix several different fixes in 
>>>>>> one fix, but since in this fix we change
>>>>>>
>>>>>> AbstractListModel to AbstractListModel<E>
>>>>>> and
>>>>>> JList(ListModel dataModel) to JList(ListModel<E> dataModel)
>>>>>>
>>>>>> I think we should also change usages of AbstractListModel  such 
>>>>>> as "this (new AbstractListModel()...)" to "this (new 
>>>>>> AbstractListModel<E>()...)" to avoid warnings.
>>>>> Ok, then it will not be a problem. Let's include this change in 
>>>>> your fix. Therefore all my comments are gone and I'm going to 
>>>>> start our internal process to commit your fix.
>>>>>
>>>>> Thanks, Pavel.
>>>>>
>>>>>>
>>>>>> If you don't agree:
>>>>>> There are several places where I changed the usage of now 
>>>>>> generified classes to the generic variant. Which ones should I 
>>>>>> change back? Only this case?
>>>>>
>>>>
>>>
>>
>