In JDK1.2fcs, even if you set -Dfile.encoding option,
it doesn't affect ByteToChar converter.
In case of JDK1.2beta4, -Dfile.encoding option affects
both ByteToChar converter and CharToByte converter.

Run the following program.

--- program ---
import sun.io.CharToByteConverter;
import sun.io.ByteToCharConverter;

public class DefaultEncoding {
    public static void main (String args[]) {
        System.out.println(ByteToCharConverter.getDefault().toString());
        System.out.println(CharToByteConverter.getDefault().toString());
    }
}

--- result ---
Win32, JDK1.2fcs_D:
C:\>java DefaultEncoding
ByteToCharConverter: SJIS
CharToByteConverter: SJIS

C:\>java -Dfile.encoding=EUC_JP DefaultEncoding
ByteToCharConverter: SJIS
CharToByteConverter: EUC_JP

Win32, JDK1.2beta4_K:
C:\>java DefaultEncoding
ByteToCharConverter: SJIS
CharToByteConverter: SJIS

C:\>java -Dfile.encoding=EUC_JP DefaultEncoding
ByteToCharConverter: EUC_JP
CharToByteConverter: EUC_JP