Very Strange java.lang.NoClassDefFoundError. Class exists in classpath

Question

Dear Forum:
Occasionally, I run into strange java.lang.NoClassDefFoundErrors.
Here is an example: I have two different classes Class1.class and Class2.class in different jars. Both use a common class: AppContext in third jar file.
If Class1 tries to use AppContext, it works just fine. However, if Class1 instantiates Class2 and Class2 tries to use AppContext, you get the nasty java.lang.NoClassDefFoundError, in the same thread.
After a struggle and trying out different orders in class / library paths, the error goes away. However, I do want to know what is the better way to understand and resolve this issue?
Here is a sample code, for illustration purposes only:
File:Class1.java_
Public class Class1
     Public Class1 ()
AppContext.getLogger().logDebug(�test1�);
//the above line works just fine.
try
Class2 something = new Class2();
catch(Error ex)
     //here we get a java.lang.NoClassDefFoundError for AppContext, which works just fine from Class1.java
     ex.printstackTrace();
File:Class2.java:_
Public class Class2
Public Class2()
AppContext.getLogger().logDebug("test2");
}

Answer 1

I think I have answer to this mystery.
This was an issue with the jdeveloper, where the jar file throwing the class not found exception was loaded by a different classloader and the jar file which could find the class was loaded by another classloader.
I forgot to mention that this was a j2ee application being run by the internal j2ee server of Jdeveloper.