Trying to load .class files in Eclipse

For a class we were given a bunch of .class files that we are supposed to use. I have them located in a folder called lib. I think I added the folder correctly to the build path correctly since a folder titled "Reference Libraries" appeared under my Project pane with a folder called lib containing all of the class files.

The problem I'm getting now is that when I try to compile the incomplete code, I get

  Exception in thread "main" java.lang.NoClassDefFoundError: Unearthed/GPRFrame
 at GPR.main(GPR.java:18)
Caused by: java.lang.ClassNotFoundException: Unearthed.GPRFrame
 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 Sou开发者_如何学运维rce)
 at java.lang.ClassLoader.loadClass(Unknown Source)
 ... 1 more

I have no idea what to do here. I just want to load the .class files so that I can continue with my project. Thanks in advance guys!

Edit: I tried putting the files in a folder lib\Unearthed and adding that to the build path but I still got the same error. I'm using eclipse to compile and run the code.

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Assuming that the class is called:

Unearthed.GPRFrame

That would mean GPRFrame.class should be in lib\Unearthed not lib\

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Are you compiling the code outside of eclipse? if yes then you have to add the lib to your classpath javac -cp lib .... if not, then i'm not so sure, eclipse should of complained with some red marks saying that it could find the class that you are using.