Casting across jar boundaries

Question

I'm seeing an odd behavior in my app where I can't cast an object back to its original type and get an
java.lang.ClassCastException: Tests.iPerf.IPerfTestResult cannot be cast to Tests.iPerf.IPerfTestResult error message.
Basically: I have 2 jars, the first a driver loads classes from the test jar.
There is an interface
TestResult
GetTestResult()
that the test jar implements to return back a subtype of TestResult.
i.e. IPerfTestResult extends TestResult.
Later on the driver calls back into the TestJar passing the TestResult it received above and the method tries to downcast from a TestResult back to the original IPerfTestResult.
This is failing.
i.e.
void
Check( TestResult Result)
IPerfTestResult Cast = (IPerfTestResult)Result;
I've added a bunch of tests. the original object can get cast back and forth as expected and even simulating the sequence by calling into a test method works fine its only when the object is stored back in code from the Driver jar and recrosses the boundary that the issue manifests.
Doing alot of tests the class name is the expected IPerfTest for Result in Check. Via reflection I can even see/access the additional fields for the subtype but
Result.class != IPerfTestResult.class even though its the same original object.
Does anyone know what's going on?
Thanks
Ben
Edited by: 808374 on Nov 8, 2010 2:21 PM

Answer 1

You cannot cast to a class that was loaded by a different classloader.