JLSv1.0 says (22.2.14):

"If a character c is in the range '\u0800' through '\uffff', then it is
 represented by three bytes, to be written in the order shown:
    (byte)(0xc0 | (0x0f & (c >> 12)))
          ^^^^^^ Should be 0xE0 !!!!!
    (byte)(0x80 | (0x3f & (c >> 6)))
    (byte)(0x80 | (0x3f & c))"

Here is the part of the source code for java.ioRandomAccessFile.writeUTF():
for (int i = 0 ; i < strlen ; i++) {
int c = str.charAt(i);
if ((c >= 0x0001) && (c <= 0x007F)) {
write(c);
} else if (c > 0x07FF) {
write(0xE0 | ((c >> 12) & 0x0F));
                    ^^^^^^^^
write(0x80 | ((c >> 6) & 0x3F));
write(0x80 | ((c >> 0) & 0x3F));
//written += 2;
} else {
write(0xC0 | ((c >> 6) & 0x1F));
write(0x80 | ((c >> 0) & 0x3F));
//written += 1;
}
}