What does "\1" represent in this Java string?

Question

System.out.println("\1");

I thought it did not compile because of the non-recognized escape sequence.

What does "\1" exactly represent?

Answer 1

It's an octal escape sequence, as listed in section 3.10.6 of the JLS. So for example:

String x = "\16";

is equivalent to:

String x = "\u000E";

(As Octal 16 = Hex E.)

So \1 us U+0001, the "start of heading" character.

Octal escape sequences are very rarely used in Java in my experience, and I'd personally avoid them where possible. When I want to specify a character using a numeric escape sequence, I always use \uxxxx.