Why Exception in thread "main" java.lang.NoClassDefFoundError:?
Solution 1
A NoClassDefFoundError
(almost) always means that your classpath is wrong. Make sure that your classpath includes the base directory of the coloredtrails
package. (Ofcourse, also make sure that the file coloredtrails\CTListener.class
actually exists).
When running from the command line:
You can set the classpath by setting the CLASSPATH
environment variable, or by specifying it with the -cp
or -classpath
option on the command line when you run your program. For example:
java -cp C:\MyProject\classes coloredtrails.CTListener
edit - Looking at the stack trace and seeing URLClassLoader
in there makes me think that you are trying to run a Java applet. To learn how to correctly deploy applets, so that all classes the applet needs can be found, see this tutorial: Deploying an Applet.
Solution 2
Sometimes, my Eclipse (Indigo on MacOSX) does that, expecially if I do changes (removing files, moving them around) to the project structure on the filsystem directly.
Basically, eclipse cannot find the source folder anymore, so he doesn't compile the source but tries to run it anyway (all this without a warning or a reference to the problem).
To fix it, remove the source folder from the build path (=right click on the src folder under the project in the package explorer, then choose "Build-path->Remove from Build-path". Then, add it again (=right click on the folder under the project in the package explorer and choose "Add to build-path"). This makes the src folder "visible" to the compiler again and fixes the problem.
Roman
Updated on July 09, 2022Comments
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Roman almost 2 years
I run my software through Eclipse. Yesterday everything was fine. I made not changes to the code but today, when I am trying to run it again I get the following error messages:
Exception in thread "main" java.lang.NoClassDefFoundError: coloredtrails/CTListener at test.DemoPlayer1.createAndShowGUI(DemoPlayer1.java:23) at test.DemoPlayer1.main(DemoPlayer1.java:39) Caused by: java.lang.ClassNotFoundException: coloredtrails.CTListener at java.net.URLClassLoader$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) ... 2 more
Why it does not see the class? What could be the reason of that? How can I resolve the problem?
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V G over 10 yearsAlternatively refresh all the files in eclipse (Shortcut F5 on the root folder in your project).
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Rudolf Real over 10 yearsI tried this and many other alternatives and didn't work. Deleting the workspace only worked for me.
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Rudolf Real over 10 yearsI had the same issue with Mavericks. I only could solve it by deleting the workspace.
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IndrekV almost 10 yearsAlso tried to re-add the src folder, but didn't work. Creating a new workspace did the trick.