It is a very old one that came with Visual J++. I also have version 1.4.2 installed, and when I compile your Demo at the command line and run it, it works correctly.
But I can't get Visual J++ to use the most up-to-date version of Java, which means I am stuck with the old version (bad programming I know, but it is only a quick & dirty app).
So my question is, can I download the sun.io.ByteToCharUS-ASCII class from somewhere?