Strange "java.lang.NoClassDefFoundError" in Eclipse

Question

I have a Java project in Eclipse perfectly running smoothly until this afternoon, when I updated some files (including a ant build.xml file). When I build the project, the following error appears:

java.lang.NoClassDefFoundError: proj/absa/FrontEnd/ApplicationStarter
Caused by: java.lang.ClassNotFoundException: proj.absa.FrontEnd.ApplicationStarter
    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)  
Exception in thread "main" 

Does anyone have a clue where the problem may be?

Answer 1

java.lang.ClassNotFoundException means CLASSPATH issues. Not having a clue implies that you're assuming that the CLASSPATH is set properly, but it's not.

If you're building with Eclipse, make sure that the directory where your compiled .class files exists, is in the CLASSPATH, and has the necessary .class files in it.

If you're building with Ant, make sure you see something like this in your build.xml:

<path id="production.class.path">
    <pathelement location="${production.classes}"/>
    <pathelement location="${production.resources}"/>
    <fileset dir="${production.lib}">
        <include name="**/*.jar"/>
        <exclude name="**/junit*.jar"/>
        <exclude name="**/*test*.jar"/>
    </fileset>
</path>

UPDATE: Either you don't have JAVA_HOME/bin in your PATH or you downloaded the JRE instead of the JDK. Check the directory where you installed Java and see if your /bin directory has javac.exe in it. If you don't have a /bin, download the JDK and install it.

If you do have a /bin with javac.exe in it, check your PATH to see that the Java /bin directory is in the PATH. Once you've set it, open a command shell and type "javac -version" to ensure that all is well.

What JDK did you tell Eclipse to use?

Answer 2

both the problem will be because of classpathref="master-classpath", please check the value is correct