<Swing Dev> What was the user doing was: Patch for NPE at BasicTreeUI$Actions.page:4470

[Jaroslav Tulach]

Hello Alexander,
if you scroll down the page with the report
http://statistics.netbeans.org/exceptions/exception.do?id=628832
you'll see list of user actions. Click on individual ones to get more info.

One of the last actions is

 5:34 PM Select in Projects 

it was invoked via keyboard shortcut (Ctrl-Shift-1). Looking at the XML file I 
found out that the actual time was 17:34:23. Then the user switched back to 
editor (again via shortcut this time Ctrl-Shift-0) about 1.5s later at 
17:34:24:

 5:34 PM Editor 

A two seconds later (at 17:34:26) the NPE from JTree appeared:

java.lang.NullPointerException
at javax.swing.plaf.basic.BasicTreeUI$Actions.page(rt.jar:4470)
at javax.swing.plaf.basic.BasicTreeUI$Actions.actionPerformed(rt.jar:4046)
at javax.swing.SwingUtilities.notifyAction(rt.jar:1664)

We don't have logs about what the user did inside of the "Projects" component 
with JTree, but there seems to be no radical tree structure changes (no 
creation or deletion of files). 

The fact that the NPE happens more than a second after the user leaves the 
JTree hosting component is surprising. But maybe the JTree was not visible 
anymore - many users (including me) have the IDE configured to hide the 
"Projects tab" as soon as we switch to editor...

I am not sure what to conclude from these observation, however.
-jt

Dne Pá 16. listopadu 2012 18:00:45, Alexander Scherbatiy napsal(a):
> On 11/16/2012 4:10 PM, Jaroslav Tulach wrote:
> > Hello Alexander,
> > thanks for your reply. The source code for NetBeans TreeView component is
> > available here:
> > http://hg.netbeans.org/main-
> > golden/file/ccea2dfe47eb/openide.explorer/src/org/openide/explorer/view/Tr
> > eeView.java I'll be glad for any review, however I am also positively
> > pleased by your
> > answer:
>      Is it possible to know from the filled NB issues which NB
> module/component has been used when the NPE occures?
>      Or could you point any NB panel where the  TreeView is used.
> 
> >>       The ui.getPathBounds(tree, newPath) method definitely can return
> >> 
> >> null so it needs to have this check.
> > 
> > Should I start working on a webrev, so (in case you don't find any
> > violation of good Swing practices in TreeView) we can eliminate this NPE
> > once and forever?
>      Yes, please.
> 
> > What should be part of such webrev? Just the NPE check? Or do you want
> > some
> > test, change in documentation, etc.?
> 
>      The fix should check the NPE and may be do some possible default
> actions in this case.
>      It is a good idea to add an automated test but it can be possible
> if there are known steps which reproduce the issue.
>      At least you can run the test/javax/swing/JTree  automated test to
> check possible regressions.
> 
>      Thanks,
>      Alexandr.
> 
> > Thanks again for your comments.
> > -jt
> > 
> > Dne Pá 16. listopadu 2012 15:30:00, Alexander Scherbatiy napsal(a):
> >> On 11/15/2012 7:58 PM, Jaroslav Tulach wrote:
> >>> Dear Swing maintainers,
> >>> my name is Jaroslav Tulach and I am maintaining NetBeans explorer - a
> >>> component that is using JTree heavily.
> >>> 
> >>>>  From time to time I receive a user report with a NPE from Swing where
> >>>> 
> >>>> little>
> >>> 
> >>> or even no NetBeans code involved. Just today I got
> >>> http://netbeans.org/bugzilla/show_bug.cgi?id=222081
> >>> We have about 35 other ones (which is not that much given the fact we
> >>> have
> >>> million of users), but still...
> >>> 
> >>> According to
> >>> http://statistics.netbeans.org/exceptions/exception.do?id=628832
> >>> the report comes from jdk7u9-b05. The source code is here
> >>> http://hg.openjdk.java.net/jdk7u/jdk7u/jdk/file/jdk7u9-
> >>> b05/src/share/classes/javax/swing/plaf/basic/BasicTreeUI.java
> >>> and thus it looks like the call on line 4468 to
> >>> 
> >>> ui.getPathBounds(tree, newPath);
> >>> 
> >>> can return null (under some rare and unknown circumstances).
> >>> 
> >>> I can close the bug #222081 as "worksforme", but it is clear that such
> >>> error happens from time to time and we don't want our users to face
> >>> errors. A simple:
> >>> 
> >>> 4469 if (newRect == null) return;
> >>> 
> >>> would do the trick. One question remains: if I try to donate such patch,
> >>> will you accept it?
> >>> 
> >>       The ui.getPathBounds(tree, newPath) method definitely can return
> >> 
> >> null so it needs to have this check.
> >> 
> >>       However, such fix can mask the real issue, for example, in the
> >> 
> >> treeState.getBounds() method where the  treeState can be instance of
> >> FixedHeightLayoutCache or VariableHeightLayoutCache class.
> >> 
> >>       If it is possible, could you send a code snippet that shows how
> >> 
> >> NetBeans uses JTree? May be it can give a hint what can be wrong in this
> >> case.
> >> 
> >>       Thanks,
> >>       Alexandr.
> >>> 
> >>> -jt