RegEx to verify variable contents/length

[Dave Bosky]

I have a session variable called myID and I need to verify that this variable contains exactly 11 digits. How can I do this using a RegEx?
I've used the pattern class to match and replace words but I'm unsure how to check this variable.
Any little snippets that I can use as a guide for future RegEx patterns?
Thanks,
Dave

[Jim Yingst]

In a pattern, you can use \d to refer to a digit. And you can specify a number of repetitions using curly braces {}, e.g.
\d{5} - exactly five digits
a-z{3,10} - from three to ten lowercase letters
\w{4,} - at least four word characters

[Michael Morris]

^[0-9]{11}$ should match an integer of exactly 11 digits but will allow 0 as the initial digit. To prevent that then use ^[1-9][0-9]{10}$
The ^ matches the beginning of a line and the $ matches the end of a line so there can be nothing else in the String for these to match.

[Michael Morris]

Yingst again!

[Jim Yingst]

Neener, neener.
The two posts do have some different info in them though, so all is not lost. I'll note that if you use matches() rather than find() (in the Matcher class) then it tries to match the entire input string, not just part of it, so the ^ $ would be unnecessary. But that only works if you know to use matches(), which I hadn't mentioned in the earlier post, so it's good that this came up.

[Dave Bosky]

I thought I had the correct syntax but it doesn't seem to be working.
Could someone lend me some eyes

import java.util.regex.*;
public class elevenDigitVariable {
public static void main(String[] args) {
try {
String billId = "21233343430";
Pattern p = Pattern.compile("[\\d{11}]");
Matcher m = p.matcher(billId);
StringBuffer sb = new StringBuffer();
boolean result = m.find();
boolean deletedIllegalChars = false;
while(result) {
deletedIllegalChars = true;
result = m.find();
}
if (deletedIllegalChars)
System.out.println("Invalid Bill ID: "+billId);
else
System.out.println("Valid Bill ID: "+billId);
}
catch (Exception ex) {
System.out.println(ex);
}
}
}

[Max Habibi]

Dave, you're working too hard

import java.util.regex.*;
public class ElevenDigitVariable {
public static void main(String[] args)
{
String billId = "21233343430";
boolean check = billId.matches("\\d{11}");
System.out.println(check);
}
}

HTH,
M

[Jim Yingst]

Dave - FYI the [ indicates a character class - what follows is a list of the values a single character may have. Inside a character class, symbols are interpreted differently than they are outside a character class. The \d and {} notations work outside a character class, not inside it.
Of course, now you've got the answer, thanks to Max's generosity. But in the future it's important to be aware that [ changes how subsequent symbols are interpreted.