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Thread: Funny NullPointerException

  1. #1
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    Default Funny NullPointerException

    Hi,

    Sorry for my bad english - I'm a Swede.

    I've written a pretty large Java Applet that runs fine with the appletviewer and in any browser if I run it from disc. But when I've uploaded it to my webpage it produces a NullPointerException. I've scaled down the program to a silly minimum in order to find out what's going wrong. Now, the code looks like this:

    import java.applet.*;
    import java.awt.Graphics;
     
    public class JavaTest extends java.applet.Applet {
     
        public class Dummy {
            public Dummy() {}
        }
        public Dummy ReturnNull() {
            return null;
        }
        public void init() {}
        public void paint(Graphics g) {}
        public void start() {}
        public void stop() {}
        public void run() {}
    }
    Don't mind the run, the original version of the applet uses a thread. However the program above generates a NullPointerException if I run it on my web page. But if I remove the function named ReturnDummy, it runs fine.

    Does anyone have an idea of why I can't have a function that returns an instance of an inner class?

    Best regards
    Marcus
    Last edited by JavaPF; December 5th, 2009 at 08:31 AM. Reason: Please use the [code] [/code] tags.


  2. #2
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    Default Re: Funny NullPointerException

    Just so that you don't think I'm a complete muppet ...

    The actual applet (not the dummy-version I just posted to show what goes wrong) is produced by my own little programming language (see link: NaaLaa). I'm trying to make it generate java applets instead of windows programs, so that not-so-good-programmers should be able to make games for the web. And it works very well as long as I run the applets from disc via the appletviewer, internet explorer or firefox. But when I put an applet on the web, the mere existance of a function that returns an instance of an inner class causes the nullpointerexception to be generated.

    /Marcus
    Last edited by Marcus; December 5th, 2009 at 08:31 AM.

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    Default Re: Funny NullPointerException

    Whats the full stack trace saying?

    // Json

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    Default Re: Funny NullPointerException

    Hi,

    The full stack trace says:

    java.lang.NullPointerException
    at sun.plugin2.applet.Plugin2Manager.findAppletJDKLev el(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager.createApplet(Unk nown Source)
    at sun.plugin2.applet.Plugin2Manager$AppletExecutionR unnable.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
    Undantag: java.lang.NullPointerException

    And it goes away when I remove that method I mentioned.

  5. #5
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    Default Re: Funny NullPointerException

    Well, I found some more:

    network: Cachepost not found [webbadress: http://www.naalaa.com/javatest$Dummy.class, version: null]
    network: Connecting http://www.naalaa.com/javatest$Dummy.class with proxy DIRECT
    network: Connecting NaaLaa with proxy DIRECT
    basic: exception: null.
    java.lang.NullPointerException
    at sun.plugin2.applet.Plugin2Manager.findAppletJDKLev el(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager.createApplet(Unk nown Source)
    at sun.plugin2.applet.Plugin2Manager$AppletExecutionR unnable.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

    I am a complete beginner when it comes to java, so I don't know exactly what this is about or what I'm talking about. But if I interpret this right, he's looking for a .class-file for the inner class. I assumed he baked them into one file - javatest.class. I guess that explains it all. Sorry for not thinking.
    Last edited by Marcus; December 6th, 2009 at 09:16 AM.

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