The following ones are valid too...
char uni = '\u0065';
char hex = 0x65;
char oct = 056;
but
char lf = '\u000a';
is not valid because this is actually a linefeed which is translated as a real linefeed in a very early stage during the parsing and the line ends up looking like
char lf = '
';
which is clearly not a valid
Java statement.