A couple years ago there was quite a bit of talk about the '.netcpu' that ran something called TinyCLR.
Sadly, that project (and its company - http://www.dotnetcpu.com
) have disappeared. I'm not sure if anything along those lines has been done since. A quick google of '.netcpu' or 'tinyclr' turned up nothing other than old articles about the defunct device/company.
Now, I'm by no means a Java expert, but Java seems much closer to C# than to C/C++ or assembly. You'd probably have little trouble picking up Java if you know C#.