RFR: 8365886: JSplitPane loses track of the left component when the component orientation is changed [v3]

[Prasanta Sadhukhan]

On Tue, 26 Aug 2025 07:11:53 GMT, Prasanta Sadhukhan <psadhukhan at openjdk.org> wrote:

>> When the component orientation is changed from LTR to RTL or the other way around, JSplitPane exchanges the left and right components. However, it does this by adding and removing components instead of swapping the leftComponent and rightComponent fields which results in leftComponent field is left as null.
>> 
>> This is because when JSplitPane calls `setLeftComponent(rightComponent)` it calls `JSplitPane.addImpl` which calls `super.addImpl`
>> which [removes] https://github.com/openjdk/jdk/blob/f423e1d9ad37135abacb8deb2d2151e21768a23e/src/java.desktop/share/classes/java/awt/Container.java#L1118 the component from the JSplitPane as it calls `JSplitPane.remove` so the sequence is
>> At start `leftComponent = Red, rightComponent = Green`
>> 
>> before `super.addImpl` is called in `JSplitPane.addImpl` the 
>> 
>> `leftComponent = Green, rightComponent = Green`
>> 
>> After super.addImpl is called, it calls [JSplitPane.remove] (https://github.com/openjdk/jdk/blob/f423e1d9ad37135abacb8deb2d2151e21768a23e/src/java.desktop/share/classes/javax/swing/JSplitPane.java#L918) where it sets
>> leftComponent = null.
>> 
>> so we have
>> leftComponent = null, rightComponent = Green and then it calls [super.remove] (https://github.com/openjdk/jdk/blob/f423e1d9ad37135abacb8deb2d2151e21768a23e/src/java.desktop/share/classes/javax/swing/JSplitPane.java#L922) which calls `JSplitPane.remove(index)` and since index=1 because "Green" is 1 it removes rightComponent 
>> so we have now
>> leftComponent = null, rightComponent = null
>> 
>> so when we now call [setRightComponent](https://github.com/openjdk/jdk/blob/f423e1d9ad37135abacb8deb2d2151e21768a23e/src/java.desktop/share/classes/javax/swing/JSplitPane.java#L382) it sets rightComponent to Red but leftComponent is not set and is still null.
>> 
>> So fix is to just swap the left and right component in setComponentOrientation call itself without using Container add/remove components
>
> Prasanta Sadhukhan has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fire property change notification instead

I understand `ORIENTATION_PROPERTY` is supposedly meant for horizontal/vertical orientation change but what the code is doing on receipt of this PropertyChange event is exactly what we want it for ComponentOrientation change which is to update the layout manager components

https://github.com/openjdk/jdk/blob/f423e1d9ad37135abacb8deb2d2151e21768a23e/src/java.desktop/share/classes/javax/swing/plaf/basic/BasicSplitPaneUI.java#L2170-L2172

https://github.com/openjdk/jdk/blob/f423e1d9ad37135abacb8deb2d2151e21768a23e/src/java.desktop/share/classes/javax/swing/plaf/basic/BasicSplitPaneUI.java#L1204-L1211

Moreover, `layoutManager` is protected field of `BasicSplitPaneUI` which is not accessible from JSplitPane

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PR Comment: https://git.openjdk.org/jdk/pull/26893#issuecomment-3235505904