Broken Eclipse project - classNotFoundException - could not find main class

Question

I have a project I've been developing in Eclipse 3.7.2 on Ubuntu 12.04. Recently, I've restructured the class hierarchy which involved moving classes between packages. I did not move my main class ("ob3.converter.Converter"), which contains my public static void main(String[] args) method.

Now, when I attempt to run it, I get:

Exception in thread "main" java.lang.NoClassDefFoundError: ob3/converter/Converter
Caused by: java.lang.ClassNotFoundException: ob3.converter.Converter
    at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
Could not find the main class: ob3.converter.Converter. Program will exit.

I've only ever really worked (in java) with Eclipse, which handles all the overhead for me - hence I have little understanding of this error or what could cause it. I've looked through my Run Configuration/Classpath etc but without knowing what to look for, it was fruitless.

Could anybody point me in the right direction? I've googled / search SO, and most things talk about a manifest file, but I've been unable to find it anywhere. My workspace folder contains nothing more than my source files.

I can verify:

• The class "Converter" exists within the package "ob3.converter".
• The class "Converter" contains a public static void main(String[] args) method.
• The "Source" tab on the Java Build Path page in Project Properties shows "converter/lib" and "converter/src" - these 2 folders contain my entire project source.
• The JRE used in Run Configuration/JRE is "java-6-openjdk-amd64".
• The ClassPath tab in Run Configuration looks like this:
  • Boostrap Entries:
    • JRE System Library [java-6-openjdk-amd64]
  • User Entries:
    • converter (default classpath)
      • converter
• The path to Converter.java has not changed since I last run it successfully.

Any help is very much appreciated!

Answer 1

I think you should rebuild your project. You can do this by clicking on Projects > Clean...

Sometimes the automatic build of Eclipse has problems with the refactoring or moving of classes.

Answer 2

I ran into this same error message. For me, I was on linux and the user issuing the java command did not have sufficient permissions to the directory of the jars on the classpath.