jar files is for java programs... the CLR doesn't understand Java bytecode, but only MSIL bytecode.
However, exist a command line program that convert java bytecode to MSIL bytecode...
Look a the MSDN documentation :
http://msdn.microsoft.com/en-us/library/sxh73yst(v=vs.80).aspx[
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Never tryed this, so i don't know the worth of this utility tool.
Enjoy, ...