How do I deal with a ClassNotLoadedException while debugging?

Question

So I'm (remotely) debugging a java/jboss application in Eclipse, stepping through line by line. At one point, an array of GridSquare objects (GridSquare is a fairly simple, standalone class, contains a few properties and methods) is created by a method call, i.e:

GridSquare[] squares = this.theGrid.getSquares(14, 18, 220, 222);

...While when I actually execute the code, the squares array does get populated with GridSquare objects, I get something odd when stepping through the code and debugging. At a breakpoint on the line immediately following the assignment shown above, if I try to view the squares array, instead of a value I get this:

org.eclipse.debug.core.DebugException: com.sun.jdi.ClassNotLoadedException: Type has not been loaded occurred while retrieving component type of array.

...Anyone know what that's about?

Answer 1

Basically it means the class loader has not loaded the GridSquare[] class. That being said it sounds like a bug in the debugger in some way. The breakpoint association with the code seems to be slightly broken. Either you need to recompile to get the line numbers in sync or some other issue is going on. At that point in the code (after the assignment) it needs to be loaded. Unless getSquares actually returns a subclass (GridSquareSubclass[]) at which point the JVM may not have loaded it because it doesn't need it (yet).

Answer 2

I ran into this error because I was running a unit test on code that uses reflection. I had made a special class for testing all the features of the code. Junit apparently uses a separate classloader for test classes (which makes perfect sense) so my code was not able to use reflection on that class. The stack trace I got was extremely generic (java.lang.InstantiationException) but when I checked in debug mode there was more detail on the Exception object itself (org.eclipse.debug.core.DebugException: com.sun.jdi.ClassNotLoadedException) which led me to this conclusion.

So I moved the special class to the main classloader (by moving the file from src/test/java to src/main/java) and it worked fine. I don't like this solution but I cannot figure out an alternative. In my case it's not a big deal but I can see how this might be a concern for others.