<Swing Dev> [9] Crash tabbing to a checkbox with custom model (see e.g. 8074883)

[Sergey Bylokhov]

Hi,
Can you please create a new CR using http://bugs.java.com <http://bugs.java.com/> ?
It is too late to fix it in jdk9, but I think it will be possible to fix it in 10 and then backport to some update of jdk9.

> 
> Good day,
> 
> I believe I've hit my first bug in occasional testingof the JDK-9 drops.
> I hope this is an appropriate way to send feedback?
> 
> We use a customised "tri-state" checkbox, which triggers a crash when the
> keyboard focus moves to it by pressing the TAB key. The issue seems related
> to some focus logic changes with button-groups introduced in JDK-9.
> (For example: 8074883?)
> 
> The top of the stack trace is:
> 
> java.lang.ClassCastException: com.example.TristateCheckBox$TristateDecorator cannot be cast to java.desktop/javax.swing.JToggleButton$ToggleButtonModel
>    at java.desktop/javax.swing.LayoutFocusTraversalPolicy.accept(LayoutFocusTraversalPolicy.java:243)
>    at java.desktop/javax.swing.SortingFocusTraversalPolicy.getComponentBefore(SortingFocusTraversalPolicy.java:435)
>    at java.desktop/javax.swing.LayoutFocusTraversalPolicy.getComponentBefore(LayoutFocusTraversalPolicy.java:143)
>    at java.desktop/java.awt.Component.transferFocusBackward(Component.java:8201)
>    at java.desktop/java.awt.Component.transferFocusBackward(Component.java:8186)
>    at java.desktop/java.awt.DefaultKeyboardFocusManager.focusPreviousComponent(DefaultKeyboardFocusManager.java:1388)
>    at java.desktop/java.awt.DefaultKeyboardFocusManager.processKeyEvent(DefaultKeyboardFocusManager.java:1183)
>    at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:4877)
>    at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2317)
>    at java.desktop/java.awt.Component.dispatchEvent(Component.java:4793)
> ...
> 
> The relevant code in LayoutFocusTraversalPolicy.accept is:
> 
>    } else if (aComponent instanceof JComponent) {
>        if (SunToolkit.isInstanceOf(aComponent,
> "javax.swing.JToggleButton")) {
>            JToggleButton.ToggleButtonModel model =
>                    (JToggleButton.ToggleButtonModel) ((JToggleButton)
>                            aComponent).getModel();   // <- Line 243
>            if (model != null) {
>                ButtonGroup group = model.getGroup(); // <- Only use of 'model'
> 
> For whatever reason (probably to do with the 3 states) the button model
> is not a ToggleButtonModel, but derived from a DefaultButtonModel.
> 
> I think a simple solution is to (check? and) cast less specifically, to a
> DefaultButtonModel instead. That looks to be sufficient here, and is also
> what we find similar code in JToggleButton doing. For example in
> JToggeleButton.getGroupSelection we see:
> 
>    if (model instanceof DefaultButtonModel) {
>        ButtonGroup group = ((DefaultButtonModel) model).getGroup();
>        //...
> 
> I note while JToggleButton creates a ToggleButtonModel by default, it
> does not enforce it via setModel().
> 
> 
> More background: I think we found this code (over a decade ago) from here
> 
>  http://www.javaspecialists.eu/archive/Issue082.html
> 
> (There are better solutions implementing this GUI control these days, but
> I thought you might like to hear about it.)
> 
> Kind regards,
> Luke Usherwood
> 
> 

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