RFR: 4797982: Setting negative size of JSplitPane divider leads to unexpected results. [v6]

[Karl T]

On Thu, 28 Jul 2022 04:07:55 GMT, Prasanta Sadhukhan <psadhukhan at openjdk.org> wrote:

>> Setting JSplitPane divider size to negative value leads to unexpected results and is not desirable and seems to be not practical.
>> I guess we should return IAE but it might break existing app so fixed to clamp it to 0 incase negative value is tried to be set for divider size.
>
> Prasanta Sadhukhan has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove implNote tag

All look and feels initially set the divider size to what they need. This is done here:

https://github.com/openjdk/jdk/blob/eab4c0c49934bd6f37a0b6174ca10e5c8708d13b/src/java.desktop/share/classes/javax/swing/plaf/basic/BasicSplitPaneUI.java#L357-L358

Each L&F uses its own divider size.
E.g. Windows L&F uses `5`:

https://github.com/openjdk/jdk/blob/0a65e8b282fd41e57108422fbd140527d9697efd/src/java.desktop/windows/classes/com/sun/java/swing/plaf/windows/WindowsLookAndFeel.java#L1247

Or Metal L&F uses `10`:

https://github.com/openjdk/jdk/blob/d4b040f42dd0a9100ad1ffa55de4ae4f20e9f182/src/java.desktop/share/classes/javax/swing/plaf/metal/MetalLookAndFeel.java#L1371

So a L&F could also use divider size zero to implement an invisible divider.
Don't see a reason, why divider size zero should be no longer allowed...

> I didn't get why some effect like the "visibility" of the divider in some L&F should be allowed to over-rule the specified size.

If the application invokes `JSplitPane.setDividerSize(int)`, then this overrules the divider size specified by the L&F.
There is a field `JSplitPane.dividerSizeSet` that is used for this.

L&Fs do not invoke `JSplitPane.setDividerSize(int)` directly. Instead they invoke `LookAndFeel.installProperty(...)`, which calls `JSplitPane.setUIProperty(...)`, which checks flag `dividerSizeSet` and does not change divider size if the application has invoked `setDividerSize(...)`:

https://github.com/openjdk/jdk/blob/096bca4a9c5e8ac2668dd965df92153ea1d80add/src/java.desktop/share/classes/javax/swing/JSplitPane.java#L1059-L1064

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PR: https://git.openjdk.org/jdk/pull/9566