RFR: 4337898: Serializing DefaultTableCellRenderer changes colors [v4]

[Phil Race]

On Mon, 1 Dec 2025 07:41:10 GMT, Prasanta Sadhukhan <psadhukhan at openjdk.org> wrote:

>> When a `JTable `using any objects of type `DefaultTableCellRenderer`, or subclasses, is serialized, 
>> the colors used to render cells in the JTable subsequent to the call to `writeObject()`
>>  are forced to the default colors for `DefaultTableCellRenderer`'s immediate base class, JLabel, causing the colors
>> defined in the JTable (typically black on white) to be ignored.
>> 
>> The problem seems to stem from a call to
>> `installUI `in the `writeObject()` method of `JLabel`, `DefaultTableCellRenderer`'s base class.
>>  This causes the `setForeground` and `setBackground` methods to be invoked with specific colors, which turn out to be JLabel's defaults.
>> Invoking these methods subsequently with parameters of null restores normal operation same as is explicitly done in `DefaultTableCellRenderer.updateUI()`
>> https://github.com/openjdk/jdk/blob/195b36f90b789b64f4a0fc867c620935d609a455/src/java.desktop/share/classes/javax/swing/table/DefaultTableCellRenderer.java#L159-L162
>> 
>> CI run is ok..
>
> Prasanta Sadhukhan has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Rethrow Exception

> > How/why does null restore the JTable-specified colors ? I don't see anything about null in the spec. And what have people been doing the last 25 years if serializing a JTable "broke" its rendering ?
> 
> Specifying null would cause `unselectedForeground` and `unselectedBackground` to be null
> 
> 
> 
> so it will fallback to table assigned foreground and background color
> 

So how do people know that ? Reading the source and trial and error don't count as ways to know.

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PR Comment: https://git.openjdk.org/jdk/pull/28549#issuecomment-3643911298