Jython NoClassDefFoundError when using a class from another class

Question

I am trying to use 2 Java defined classes in python using jython 2.7.0 but after i ran my script it throws a java.lang.NoClassDefFoundError

Those are my 2 Java classes:

Hello.java

package hello;

public class Hello {
    public void printMsg(){
        System.out.println("check out this cool message");
    }
}

Hello2.java

package hello;

public class Hello2 {
    public void printHelloMsg(){
        Hello msg = new Hello();
        msg.printMsg();
    }
}

I compiled them with:

hello$ javac Hello.java Hello2.java

Then created a jar file with:

hello$ jar cf hello-jar.jar *.class

And my python script that is supposed to use the Hello2 class, which uses Hello class:

hello.py

import Hello2

h = Hello2()
h.printHelloMsg()

After i ran my script with jython using:

hello$ jython -J-cp ./hello-jar.jar hello.py

Traceback (most recent call last):
  File "hello.py", line 1, in <module>
    import Hello2
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:760)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
    at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:411)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:348)
    at org.python.core.Py.loadAndInitClass(Py.java:991)
    at org.python.core.Py.findClassInternal(Py.java:926)
    at org.python.core.Py.findClassEx(Py.java:977)
    at org.python.core.packagecache.SysPackageManager.findClass(SysPackageManager.java:133)
    at org.python.core.packagecache.PackageManager.findClass(PackageManager.java:33)
    at org.python.core.packagecache.SysPackageManager.findClass(SysPackageManager.java:122)
    at org.python.core.PyJavaPackage.__findattr_ex__(PyJavaPackage.java:134)
    at org.python.core.PyObject.__findattr__(PyObject.java:946)
    at org.python.core.packagecache.PackageManager.lookupName(PackageManager.java:141)
    at org.python.core.JavaImporter.find_module(JavaImporter.java:40)
    at org.python.core.JavaImporter.find_module(JavaImporter.java:26)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)

java.lang.NoClassDefFoundError: java.lang.NoClassDefFoundError: Hello2 (wrong name: hello/Hello2)

What could possibly be the problem here? Thanks in advance

Answer 1

The problem is in the file hello.py. The import statement is incorrect; it should be:

from hello import Hello2

instead of

import Hello2