Re: Question about createUI() method?

[Roman Kennke]

Am Dienstag, den 06.09.2005, 21:13 +0000 schrieb David Gilbert:
> Hi,
> 
> A quick question about Swing:
> 
> A lot of the createUI() methods in the look and feel code are implemented 
> with a 
> HashMap to retain references to the UI delegates that are created.  For 
> example:
> 
>    public static ComponentUI createUI(JComponent component)
>    {
>      if (instances == null)
>        instances = new HashMap();
> 
>      Object o = instances.get(component);
>      MetalComboBoxUI instance;
>      if (o == null)
>        {
>       instance = new MetalComboBoxUI();
>       instances.put(component, instance);
>        }
>      else
>        instance = (MetalComboBoxUI) o;
> 
>      return instance;
>    }
> 
> I was wondering if anyone can explain the purpose of retaining the instance 
> for each 
> component?  (As opposed to just returning a new instance for each call).  As 
> I 
> understand it, the createUI() method will only be called once for each 
> component 
> each time the look and feel is changed.  So I don't see the need for 
> retaining the 
> instances in the HashMap.  Any pointers?

That was introduced by me. Honestly I don't remember myself why I found
this important. I think I might have been mislead of the API docs in
ComponentUI.createUI(): 'If the UI delegate is stateful, then it should
return a new instance per component.'

I think it would be ok to change this to simply return a new instance on
each call without storing them in the hashtables.

Best regards,
Roman