Question

Here is the simplified version of the problem:

 SomeClass c = (SomeClass) obj.getSomeClassParent()

not always but it happens sometimes to trigger exception

 org.somepackage.SomeClass can't be cast to org.somepackage.SomeClass 

How is this possible ? I suppose it has something to do with the fact that JAI imageio is native lib, but relay how can this happen ? I’m probably missing something but what ?

I'm using JAI imageio version 1.1 
dcm4che 2.0.21  DICOM lib

Here is the original code

  ImageInputStream iis = ImageIO.createImageInputStream(src);
  Iterator<ImageReader> iter = ImageIO.getImageReadersByFormatName("DICOM");
  ImageReader reader = iter.next();
  DicomImageReadParam param = (DicomImageReadParam) reader.getDefaultReadParam();

And the original exception

org.dcm4che2.imageio.plugins.dcm.DicomImageReadParam can't be cast to    
org.dcm4che2.imageio.plugins.dcm.DicomImageReadParam

Exception Image http://img215.imageshack.us/img215/3894/exception.jpg

Answer 1

I think it can happen if

1. a SomeClass instance was loaded from ClassLoader X (so its class is SomeClass of CL X or let’s call it: CL(X).SomeClass)
2. but it is being cast in a different class loader. E.g. the current Threads class loader is Y so SomeClass is actually CL(Y).SomeClass

So you have:

• instance class = CL(X).SomeClass
• class cast target = CL(Y).SomeClass

Or in other words – not the same class – thus the class cast exception.

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Possible duplicate of: ClassCastException when casting to the same class – it has some good suggestions as well.