String illegal escape charcter

Question

While answering one of the question, I came across this interesting situation.

If I have string like the following, Netbeans does not complain that it's an illegal start of expression.

String temp="\19825655.";

As soon as I remove '1' it complains that it's an illegal start of expression.

String temp="\9825655.";

couldn't figure out the reason for this behavior. Any input would be appreciated.

Observation: It seems \9 and \8 has special meaning. Only for \9 and \8 I am getting illegal start of expression. All other combinations it is not complaining.

Answer 1

\1 is an octal escape code. Check it out in the JLS in Escape Sequences for Character and String Literals.

Answer 2

Right, so what this means is that the combination \1 is an escape sequence. However, to my knowledge it isn't a known escape sequence.

EDIT: OK it's an octal number, interesting - \x Escape in Java?