hexadecimal regex

[Vonique Leary]

"Let's say that we want to create a regex pattern to search for hexadecimal literals. As
a first step, let's solve the problem for one-digit hexadecimal numbers:
0[xX][0-9a-fA-F]"

source: "12 0x 0x12 0Xf 0xg"
index: 012345678901234567

This is from Kathy Sierra and Bates SCJP book page 492 regarding regex. I don't quite understand why the index goes from 0 to 9, then from 0 to 7 rather than from 0 to 18. And the explanation says that the regex returns position 6 and 11, but I don't see any 11. What am I missing?

[Jeff Verdegan]

Array indices in Java start at zero. So if I have

int[] x = {2, 4, 6};

then x.length is 3, and x has indices 0..2, where x[0] is 2, x[1] is 4, and x[2] is 6.

The index line you show is just a shorthand to show you where you are in the given group of 10.

          11111111
012345678901234567
^          ^
|          |
+-zero     +-eleven

They just didn't show the top line indicating the tens value.

And it should have lined up like:

source: "12 0x 0x12 0Xf 0xg"  
index :  012345678901234567  

[Vonique Leary]

Well, that is simple enough. Thanks so much for the explanation!

Vonique