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Java Forum / General / June 2005Strange null-pointer
Hello, Sometimes (not very frequent thank god) I get the following NullPointerException when i start my application. If I just restart the application (i.e no change in the code) it starts fine. As you can see it is constructors that cause this. What is strange is that on the line in EventLog that causes this is this line: private JFileChooser filec= new JFileChooser(); (and in MainWindow I have private EventLog eventLog = new EventLog(); ) So what can be the issue here? Is it something I do that I should not, or is it something I don't do that I should? I kind of feel I am actually innocent of causing this, but I may be wrong of course :) any thoughts are welcome. java.lang.NullPointerException at javax.swing.ImageIcon.<init>(ImageIcon.java:161) at javax.swing.ImageIcon.<init>(ImageIcon.java:147) at com.sun.java.swing.plaf.windows.WindowsFileChooserUI$ShortCutPanel.<init>(WindowsFileChooserUI.java:603) at com.sun.java.swing.plaf.windows.WindowsFileChooserUI.installComponents(WindowsFileChooserUI.java:361) at javax.swing.plaf.basic.BasicFileChooserUI.installUI(BasicFileChooserUI.java:130) at com.sun.java.swing.plaf.windows.WindowsFileChooserUI.installUI(WindowsFileChooserUI.java:176) at javax.swing.JComponent.setUI(JComponent.java:449) at javax.swing.JFileChooser.updateUI(JFileChooser.java:1701) at javax.swing.JFileChooser.setup(JFileChooser.java:345) at javax.swing.JFileChooser.<init>(JFileChooser.java:320) at javax.swing.JFileChooser.<init>(JFileChooser.java:273) at se.wexiodisk.service.EventLog.<init>(EventLog.java:69) at se.wexiodisk.service.MainWindow.<init>(MainWindow.java:72) at se.wexiodisk.service.Diagnosetool.<init>(Diagnosetool.java:37) at se.wexiodisk.service.Diagnosetool.main(Diagnosetool.java:53) regards Daniel I realize, I should probably post my java version as well. so here is the output from java -version java version "1.4.2_01" Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_01-b06) Java HotSpot(TM) Client VM (build 1.4.2_01-b06, mixed mode) Running on windows 2000 /daniel > java version "1.4.2_01" Java versions of 1.4.2 had a security flaw that was fixed in version 1.4.2_06. You should upgrade, though upgading to 1.5.0_03 makes more sense.  SignatureAndrew Thompson http://www.PhySci.org/codes/ Web & IT Help http://www.PhySci.org/ Open-source software suite http://www.1point1C.org/ Science & Technology http://www.LensEscapes.com/ Images that escape the mundane > Hello, > Sometimes (not very frequent thank god) God does not lower Himself to bit twiddling, but I see you believe in an interprogamist God. >...I get the following > NullPointerException when i start my application. It is almost impossible to interpret a stacktrace when you cannot match the line numbers in the trace back to the code snippet. Insread I suggest an SSCCE. <http://www.physci.org/codes/sscce.jsp>. >..If I just restart > the application (i.e no change in the code) it starts fine. As you > can see it is constructors that cause this. Really? >...What is strange is that on > the line in EventLog that causes this is this line: [quoted text clipped - 5 lines] > So what can be the issue here? Is it something I do that I should not, > or is it something I don't do that I should? Yes. > I kind of feel I am actually innocent of causing this, but I may be > wrong of course :) You almost certainly are (wrong, that is). > any thoughts are welcome. Supply an SSCCE. But then, looking at your stack trace.. > java.lang.NullPointerException > at javax.swing.ImageIcon.<init>(ImageIcon.java:161) ..images often load asynchronously in Java. You possibly need to add a MediaTracker to the image loading. SignatureAndrew Thompson http://www.PhySci.org/codes/ Web & IT Help http://www.PhySci.org/ Open-source software suite http://www.1point1C.org/ Science & Technology http://www.LensEscapes.com/ Images that escape the mundane >>..If I just restart >> the application (i.e no change in the code) it starts fine. As you >> can see it is constructors that cause this. > >Really? yes, just a restart and all works fine. >You almost certainly are (wrong, that is). I was afraid thatwould be the case :) >> any thoughts are welcome. > [quoted text clipped - 6 lines] >..images often load asynchronously in Java. You possibly >need to add a MediaTracker to the image loading. but also, looking in the stacktrace. it is in the JFileChooser this happens. I.e out of my control. Neither of the classes that figures in this stacktrace loads any images. (classes I have written) So I can not add a MediaTracker. I will try to see if I can reproduce the problem with an SSCCE, I have not run into this problem before. Tracing back to code lines only gives you what I wrote. i.e two calls to constructors. As I said, my feeling is that it is something going wrong when the JFileChooser loads one of it's images.. But I can of course not be sure. I will probably upgrade fairly soon though, hopefully this problem will go away then. > java.lang.NullPointerException > at javax.swing.ImageIcon.<init>(ImageIcon.java:161) [quoted text clipped - 3 lines] > at > com.sun.java.swing.plaf.windows.WindowsFileChooserUI.installComponents(WindowsFileChooserUI.java:361) It would seem your JRE install is broken; the Windows L&F cannot find the icon images it needs for JFileChooser. Try setting a different L&F and see how it behaves then. > It would seem your JRE install is broken; the Windows L&F cannot find > the icon images it needs for JFileChooser. The OP mentioned it would work the second time. I cannot see how the JRE install could be broken the first time but not the second.. SignatureAndrew Thompson http://www.PhySci.org/codes/ Web & IT Help http://www.PhySci.org/ Open-source software suite http://www.1point1C.org/ Science & Technology http://www.LensEscapes.com/ Images that escape the mundane > > It would seem your JRE install is broken; the Windows L&F cannot find > > the icon images it needs for JFileChooser. > > The OP mentioned it would work the second time. I cannot see > how the JRE install could be broken the first time but not the > second.. /Maybe/ that could happen with a network installation. If there's some Sun code somewhere that assumes that the icon image will be available instantly, but that assumption fails when the icon has to be fetched across a network. In the subsequent attempt the OS might have the file data cached, so this time it suppled the data faster and /presto/ it works ! Pure speculation, of course... -- chris > Pure speculation, of course... 'An SSCCE is worth a thousand speculations.' ;-) [ Having said that, you'll probably turn out to have 'hit the nail on the head'! ] SignatureAndrew Thompson http://www.PhySci.org/codes/ Web & IT Help http://www.PhySci.org/ Open-source software suite http://www.1point1C.org/ Science & Technology http://www.LensEscapes.com/ Images that escape the mundane >> Pure speculation, of course... > >'An SSCCE is worth a thousand speculations.' ;-) > >[ Having said that, you'll probably turn out to have >'hit the nail on the head'! ] fraid that's not the case. it is a local installation. running from a local device. I just find it really strange. Usually re-running the code gives the same kind of problem. especially in cases like this. But this time re-running the application will cause it to work. Most strange. I guess it may be an issue with the 1.4.2 version of java. But I've done quite a bit of programming with this installation and it has never caused any problems before. As I said I will try to reproduce the problem with a SSCCE, but I highly doubt it is possible, since I have problems reproducing it as it is! (which indicates a threading issue I think. so I think the idea that java loads images asynconisly is probably what it boils down to. *most* of the time it is not a problem, but every once in a while it causes some problems.) regads Daniel > But this time re-running the application will cause it to work. Most > strange. > I guess it may be an issue with the 1.4.2 version of java. It is likely an issue with messing up threading in your code. You did follow the single-tread rule for Swing, didn't you? You also did check Sun's bug parade, didn't you? /Thomas SignatureThe comp.lang.java.gui FAQ: ftp://ftp.cs.uu.nl/pub/NEWS.ANSWERS/computer-lang/java/gui/faq >> But this time re-running the application will cause it to work. Most >> strange. >> I guess it may be an issue with the 1.4.2 version of java. > >It is likely an issue with messing up threading in your code. You did >follow the single-tread rule for Swing, didn't you? this I did. but as the problems occur in the constructors, so unless I've missunderstood the single-thread rule, it is okay to create the components in any thread, and then just make sure I show them via EDT, or must they be constrcuted in EDT as well? >You also did check Sun's bug parade, didn't you? that I have not done, but I wil have a look there now. regards Daniel >>> But this time re-running the application will cause it to work. Most >>> strange. [quoted text clipped - 9 lines] >>You also did check Sun's bug parade, didn't you? >that I have not done, but I wil have a look there now. I have now looked in the bug reports and yes it is there. Bug ID 4711700 The exact problem I have, so that means it is not a problem with my code, just the version of jvm I run. Thanks for all your input. regards Daniel >>On Fri, 17 Jun 2005 18:21:08 +0200, Thomas Weidenfeller >> >>>> But this time re-running the application will cause it to work. Most >>>> strange. >>>> I guess it may be an issue with the 1.4.2 version of java. >>>You also did check Sun's bug parade, didn't you? >>that I have not done, but I wil have a look there now. > I have now looked in the bug reports and yes it is there. Bug ID > 4711700 The exact problem I have, so that means it is not a problem > with my code, just the version of jvm I run. OK - I notice it is fixed in 1.5 <http://java.sun.com/j2se/1.5.0/fixedbugs/fixedbugs.html> Here are two strategies you might try. 1) Use WebStart (or is it an applet? ..also <object>/<embed> or the JaveVersionApplet) to ensure users have a minimum version of Java 1.5. 2) Change the code to either avoid that situation or account for it's possible behaviour in 1.4. SignatureAndrew Thompson http://www.PhySci.org/codes/ Web & IT Help http://www.PhySci.org/ Open-source software suite http://www.1point1C.org/ Science & Technology http://www.LensEscapes.com/ Images that escape the mundane >OK - I notice it is fixed in 1.5 ><http://java.sun.com/j2se/1.5.0/fixedbugs/fixedbugs.html> [quoted text clipped - 7 lines] >2) Change the code to either avoid that situation or account >for it's possible behaviour in 1.4. yeah, my thoughts go along option 2 there. Although I think most of my users will have 1.5. My idea is to catch the nullpointer and if it happenes (it happens so rarely) pop up a JOptionPane telling the user that "something bad happened, please restart the application, this problem is fixed in java 1.5" Kind of like the ostrich algortihm :) >>2) Change the code to either avoid that situation or account >>for it's possible behaviour in 1.4. > yeah, my thoughts go along option 2 there. Although I think most of my > users will have 1.5. My idea is to catch the nullpointer and if it > happenes (it happens so rarely) pop up a JOptionPane telling the user > that "something bad happened, please restart the application, Given you can catch the NPE there may be better ways to deal with the problem, including starting a thread that waits a few moments before creating the chooser. That way the user never needs to hear 'something bad happened'.. SignatureAndrew Thompson http://www.PhySci.org/codes/ Web & IT Help http://www.PhySci.org/ Open-source software suite http://www.1point1C.org/ Science & Technology http://www.LensEscapes.com/ Images that escape the mundane >>>2) Change the code to either avoid that situation or account >>>for it's possible behaviour in 1.4. [quoted text clipped - 8 lines] >a few moments before creating the chooser. That way the >user never needs to hear 'something bad happened'.. hmm, true. I'll talk to the project manager and see what they think on the subject. But since it is such unusual thing, I hardly doubt it's really worth the effort. But I'll talk to him nonetheless and see what he thinks about it. Thanks for your input regards Daniel >>>>2) Change the code to either avoid that situation or account >>>>for it's possible behaviour in 1.4. [quoted text clipped - 17 lines] > regards > Daniel Look at the discussion in the bug report. Several users provided workaround methods. For example, x-root on 17 Dec 2003. SignatureIan Shef 805/F6 * These are my personal opinions Raytheon Company * and not those of my employer. PO Box 11337 * Tucson, AZ 85734-1337 * > Daniel <daik.no-spam@mds.nospam.mdh.se> wrote in (NPE in dialog due to PLAF icon) >>>>> 2) Change the code to either avoid that situation or account >>>>> for it's possible behaviour in 1.4. .. >>>> yeah, my thoughts go along option 2 there. .. >>>Given you can catch the NPE there may be better ways to >>>deal with the problem, including .. .. > Look at the discussion in the bug report. Well.. that is a very good point Ian. Wish I'd had the sense to do that, some (checks watch) 3 and a half days before you first mentioned it! >..Several users provided > workaround methods. For example, x-root on 17 Dec 2003. Yeah. I notice a couple of strategies - besides the 'wait and retry', Larry (Barowski) proposed a solution as well, though he mentions the worrying '(..fix) most of the time'. But ultimately, there are a number of things that can be done to correct this problem - including 'if all else fails - use a PLAF that works ..or the AWT!' this last on the basis that the user would probably prefer to see an 'ugly' dialog than either a) nothing or b) a dialog telling them 'their' Java is defective and they need to upgrade (sometimes it is necessary - but not here) <my recommendation> This is definitely not a 'tell the user something bad happened' situation. Just *make* it work! </my recommendation> SignatureAndrew Thompson http://www.PhySci.org/codes/ Web & IT Help http://www.PhySci.org/ Open-source software suite http://www.1point1C.org/ Science & Technology http://www.LensEscapes.com/ Images that escape the mundane Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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