JavaXPCOM and "Native code only!"

Hi,

is it possible to implement components in Java code by implementing a 
JavaXPCOM interface? E.g. I'd like to implement a custom nsIChannel and 
nsIInputStream in Java.

Unfortunately, the read() methods in nsIInputStream are marked as "Native 
code only!" and are not available in the nsIInputStream Java interface, so 
I'm wondering how my custom stream could provide those.

Thanks,
Carsten