Hello , i'm kind of new to java. I use eclipse and i imported some jar files with some classes by going to properties -> Add External Jars; The problem is that when i try to use a class from the jar i get the following exception:

Exception in thread "main" java.lang.NoClassDefFoundError: nextapp/echo2/app/event/ActionListener at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(Unknown Source) at java.security.SecureClassLoader.defineClass(Unknown Source) at java.net.URLClassLoader.defineClass(Unknown Source) at java.net.URLClassLoader.access$000(Unknown Source) 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) at java.lang.ClassLoader.loadClassInternal(Unknown Source) at Program.main(Program.java:12) Caused by: java.lang.ClassNotFoundException: nextapp.echo2.app.event.ActionListener 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) at java.lang.ClassLoader.loadClassInternal(Unknown Source) ... 13 more

The class is supposed to create a window, i guess that the jar has to import somehow other stuff or something like that, How can i fix this?

PS. Sorry for the bad code , i don't know tags here.

thansk, Raxvan