Question

I’m new to regular expressions and for a project I’m working on I was required to validate a field to see if the 10 digit number entered contained all the same numbers.

I found the following solution:

([1-9])\\1{9}

source: http://www.coderanch.com/t/461871/java/java/Check-if-number-contains-all

I have tried to Google it, but nothing that explains what the expression is doing. I was wondering if someone could explain how this expression works.

Answer 1

It works like this:

([1-9])   // Capture any number 1-9 and store it as the first "capture"
\1        // Substitute the first "capture" as raw text into the regex
{9}       // Match that raw text another 9 times (i.e. 10 in total)

Be sure that 0000000000 shouldn’t match your expression since this isn’t matched by [1-9]