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Asked: 2026-05-12T21:08:09+00:00

Quick personal background: I was hired a few months ago as the sole .NET

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Quick personal background: I was hired a few months ago as the sole .NET developer (C#) by a company whose other devs are all php devs. A week into the job I was told they wanted to switch to Java instead of doing .NET. Not an ideal situation, but I’m trying to make it work.

I don’t think I understand the relation between a project’s library and the class path. I am using NetBeans 6.7.1 for development. My current project is to create an application that will update multiple merchant sources (eBay, Amazon, etc). I created a Class Library project that handles scheduling of these updates. We’ll call it Update.

I am in the process of creating Class Library projects for the various sources (e.g. eBay). I added the ebay project to the Update project as a Library. In the IDE there is a box that says “Build Projects on Classpath” which is checked.

Finally, right now I have a little console app that has the Update project referenced as a Library (so the ebay project is now 2 libraries deep) in the same manner. It works with code in the Update project.

This works OK until I get to instantiating a class (from the Update project via the console app) that is in the ebay project. At that point I get a 

Exception in thread "main"
java.lang.NoClassDefFoundError

which is 

 Caused by: java.lang.ClassNotFoundException
  at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
  at java.security.AccessController.doPrivileged(Native Method)
  at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
  at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
  at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
  at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
  at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)

These projects all build fine but this runtime exception is killing me. I don’t know if I really understand what adding a Library to a project does and if there is something more I need to do to make the class accessible. I’m used to being able to add a reference to a DLL and being good to go. I don’t understand why I don’t get any compiler errors or build errors but I get run time errors about accessibility. I’m guessing the classpath is a missing piece that I don’t understand too well, although I suppose it’s possible this problem has to do with something else entirely.

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1 Answer

  1. Editorial Team

    The solution I have come up with for now:

    I expected the references from nested libraries to “bubble up”. This apparently doesn’t work for classpaths. My structure was basically:

    A has reference to B has reference to C

    When I ran A it worked fine until it got to something in C. What I did was give A a direct reference to C by adding it as a library to the project. From some quick Google searches it looks like this pretty much IS how you add a classpath to a project in NetBeans.

    It seems a bit messy to me and maybe there is a better way to do that, but it has fixed my problems for now. Thanks to everyone who answered – while no one precisely solved my particular problem (you guys got me about 95% of the way there though) they verified my thoughts and enabled me to figure out that last little bit to get it going.

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